Expression and Dexamethasone Regulation of the Human ...

THEJOURNAL OF BIOLOGICAL CHEMISTRY

Vol. 263, No. 12, Issue of April 25, pp. 5846-5852, 1988 Printed in U.S.A.

0 1988 by The American Society for Biochemistry and Molecular Biology, Inc.

Expression and Dexamethasone Regulation of the Human Corticotropin-releasing Hormone Gene in a Mouse Anterior Pituitary Cell Line* (Received for publication, July 28, 1987)

Gail K. AdlerS, Cynthia M. Smas, and JosephA. Majzoub From the Neuroendocrine Genetics Laboratory,Howard Hughes Medical Institute, EndocrinelHypertension Diuision, Department of Medicine, Brighum and Women’s Hospital, Haruard Medical School, Boston,Massachusetts 02115

The factors controlling the expression of corticotro- fore isolated the hCRH gene from a human genomic library pin-releasing hormone (CRH), a hypothalamic neuro- and introduced thegene into theheterologous mouse cellline peptide involved in the regulationof ACTH secretion, AtT-20, generating stably transformed lineswhich expressed are poorly understood partly because a suitable in vitrothe hCRHgene. In this report, we demonstrate that the hCRH model is lacking. To studythe regulationof CRH gene gene is correctlyexpressed in this system and is appropriately expression, an 8-kilobase (kb) DNA fragment contain- negatively regulated by glucocorticoid. ing the entire human CRH gene as well as approximately 6 kb of 5‘ sequence and 0.8 kb of 3‘ sequence MATERIALSANDMETHODS was isolated from a X Charon 4A human genomic liIsolation of a Bacteriophage Clone Containing the Human Preprobrary and introduced into a mouse anterior pituitary cell line, AtT-20, by Capo4 transfection with a neo- corticotropin-releasing Hormone Gene-A X Charon 4A genomic limycin-selectable marker. Approximately 10%of the brary constructed from human fetal liver was screened for phage containing the preprocorticotropin-releasing hormone geneby the neomycin-resistantlinesstablyexpressed the CRH procedure of Benton and Davis (3). Two 62-base long oligonucleotide gene and secreted radioimmunoassay-detectableCRH probes corresponding to the 5’ (hCRH 1) and 3’ (hCRH 2) portions into culturemedia at levels greater than100 pg/ml. By of the 41-amino acid CRH peptide were synthesized by the phosphite Southern blot analysis the 8-kb DNA fragment con- triester method (4) using an Applied Biosystems Model 380A DNA taining theCRH gene had been incorporated intact into synthesizer (Fig. 1).These oligonucleotides were radioactively labeled the AtT-20 genome. In each CRH-producing strain, with [Y-~’P]ATP(Amersham Corp.) and T4 polynucleotide kinase but not in the parent AtT-20 cell line, we detected by (Bethesda Research Laboratories) (5) andused to screen the genomic Northern blot analysis anRNA species that hybridized phage library. Approximately 0.5 X lo6 cpm of probes hCRH 1 and 2 to two radioactivecRNA probes specific for either the were used to probe separate filters in duplicate. Filters were hybridized overnight at 45 “C, washed at 45 “C (6), and exposed to x-ray 5’ or 3’portion of CRH mRNA, and that co-migrated film (Kodak XAR-5) at -80 “C with an intensifying screen. with placentalCRH mRNA. Dexamethasone treatment A plaque which hybridized to both probes was identified, and for 24-96 h caused a specific decrease in CRH mRNA bacteriophage DNA was isolated using the procedure of Maniatis et and peptide levelsof 40-50% in the fiveCRH-produc- al. (7). Southern blot analysis of this bacteriophage DNA revealed an ing cell lines with half-maximal suppression at -lo-’ 8-kb EcoRI fragment which hybridized to hCRH 1. Restriction enzyme analysis with SstI, BglII, HindIII, PstI, EcoRI, and PuuII, as M dexamethasone, indicating that CRH gene expression is negatively regulated by glucocorticoids. Thus, well as DNA sequence analysis from nucleotides 210-310 (Fig. 1) (data not shown),were consistent except for one nucleotide with the wehaveestablished an in vitro model suitable for studying in detail those cis- and trans-acting factors previously published map of the hCRH gene (8). Plasmid Constructions-This 8-kb hCRH gene fragment was subwhich regulateCRH gene expression. cloned into the EcoRI site of pUC-13 (9) and pSV2-neo (10) to Corticotropin-releasing hormone (CRH)’ ais41-amino acid neuropeptide synthesized in the paraventricular nucleus of the hypothalamus and released into the hypophyseal-portal system in response to stress (1).It has a major role in the regulation of the hypothalamic-pituitary-adrenal axis via its stimulation of pro-opiomelanocortin gene expressionand ACTH release in the anterior pituitary. The factors controlling the expressionof the human CRH (hCRH)gene, located on the long arm of chromosome 8 (Z), are poorly understood partly because a suitable in uitro model is lacking. We there* The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked “aduertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact. $ To whom correspondence should be addressed. The abbreviations used are: CRH, corticotropin-releasing hormone; ACTH, adrenocorticotropic hormone; hCRH, human CRH; kb, kilobase; POMC, pro-opiomelanocortin.

generate pPC-g-hCRH-1001+ and pSV-g-hCRH-1001+, respectively (Fig. 2). The 652-base pair SstI-SphI fragment containing the coding region of the CRH gene was subcloned into the corresponding sites in Bluescribe (Stratagene), generating plasmid pBS-g-hCRH-1002. The 375-base pair XmnI-PstI fragment which contains part of the 5”untranslated region of the CRH gene was subcloned into Bluescribe at the SmaI-PstI sites, generating plasmid pBS-g-hCRH-1005. A 0.9-kb HindIII-EcoRI fragment containing the coding region of the mouse pro-opiomelanocortin (POMC) cDNA was isolated from pMKSU16 (11)and subcloned into the HindIII-EcoRI sites of Bluescribe, generating pBS-c-mPOMC-1100. pSV2-neo was digested with HindIII and AuaI to release a 1-kb fragment containing the coding sequence for the neomycin-resistant gene. This HindIII-AuaI fragment was subcloned into the HindIII-AuaI sites of Bluescribe, generating pBS-neo. Plasmid DNA was isolated using the procedure of Birnboim and Doly (12). Synthesis of Radwactiuely Labeled cRNA Probes-”P-Labeled antisense-strand cRNA probes were synthesized using [cI-~’P]UTP (Amersham Corp.) as described (13) except that unincorporated nucleotide was separated from RNA by affinity chromatography on an Elutip column (Schleicher & Schuell). Probe hCRH 3 was synthesized from EcoRI-digested pBS-g-hCRH-1002 using T3 RNA polymerase and probe hCRH 4 from EcoRI-digested pBS-g-hCRH-1005 using T3 RNA polymerase. Mouse POMC cRNA probe was made from

5846

Expression and Dexamethasone Regulation of the hCRH Gene HindIII-digestedpBS-c-mPOMC-110 usingT7 RNA polymerase, and neomycin cRNA probe was synthesized from HindIII-digested pBSneo using T7 RNA polymerase. Cell Culture and Transfection of AtT-20 Cells-The AtT-20/D16v (AtT-20) mouse anterior pituitary cell line was grown in Ham's F10 media (Gibco) containing 2.5% fetal bovine serum (Hyclone), 15% horse serum (Hyclone), 50 units/ml penicillin (Gibco), and 50 bg/ml streptomycin (Gibco) under a 5% CO,, 95% air atmosphere at 37 "C. Media were changed every 3-4 days, and cells were passaged approximately every 2 weeks when about 70% confluent. AtT-20 cells were collected by gently washing the attached cells for 10-15 s with a trypsin solution (0.05% trypsin, 5.4 mM KCl, 137 mM NaCl, 5.6 mM dextrose, 6.0 mM NaHC03, 0.5 mM EDTA). The solution was then removed and the cells incubated at 37 "C for 5 min, harvested in phosphate-buffered saline (Gibco), and centrifuged at 1500 rpm for 10 min to obtain a cell pellet. Stable AtT-20 transfectionswere carried out by the calcium phosphate precipitation technique (14) as modified by Comb et al. (15) using the neomycin-resistant gene on either pRSVneo (16) or pSV2neo as a selectable marker. AtT-20 cells were plated at 10' cells/cm2 1 day prior to transfection and grown in media containing 10% fetal bovine serum. Cells were re-fed 3 h prior to the addition of calcium phosphate-DNA precipitate and glycerol-shocked 4 h after transfection. After 48 h, 0.25 mg/ml G418 (Gibco, approximately 50% active) FIG. 1. Schematic representation " of the locations of cRNA and cDNA probes complementary to the hCRH gene which were used in this study. Boxed region, DNA sequence encoding prepro-CRH; solid boxed region, DNA sequence encoding CRH peptide; ZVS, 800-nucleotide-long intervening sequence; CAAAT, TATA, putative promoter elementsin the 5"flanking region of the hCRH gene; hCRH 1, hCRH2, synthetic oligonucleotide cDNA probes; hCRH 3, hCRH4, cRNA probes.

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was added to the media. Approximately 3 weeks later G418-resistant clones were selected and transferred to 96-well dishes. Individual clones were screened for CRH secretion into the media. CRH peptide was measured by a commercial radioimmunoassay kit (Peninsula Laboratories) with a detection limit of 100 pg/ml. Established G418resistant cell lines were grown without G418 selection. Characterization of CRH-secreting Cell Lines-CRH secretion into the media by CRH-producing cell lines was measured over time. Each cell line was plated a t a concentration of 6.5 X lo3 cells/cm2 in a 24well plate. 4 days later when the cells were in active growth (average doubling time of 27 h over the next 2 days) the media in each well were replaced with 1 ml of fresh media. At three time points after the media change, 6, 24, and 48 h, media were collected for CRH radioimmunoassay, and cells were collected for protein assay (Bio-Rad). The ability of dexamethasone to influence CRH expression was measured in CRH-producing cells lines. Cells from each strain were plated a t 6.5 X lo3 cells/cm* and grown for 5 days. Thereafter, media were changed daily with experimental cells receiving dexamethasone dissolved in absolute ethanol, and the control cells receiving ethanol alone. After the appropriate incubation period, total RNA was prepared and characterized by RNA filter (Northern) blot hybridization analysis (see below). Media were assayed for CRH and ACTH, and cells were collected for protein assay. ACTH was measured by radioimmunoassay using a commercial kit (Nichol's Laboratories, San

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FIG. 2. hCRH gene constructions transfected into mouse AtT-20 cells. Panel A , pPC-g-hCRH-1001, consisting of an 8-kbhCRH genomic fragment ligated into the EcoRI site of pUC-13, was cotransfected along with pRSVneo into AtT-20 cells. Panel B, pSV-g-hCRH-1001, consisting of an 8-kb hCRH genomic fragment ligated into the EcoRI site of pSVneo, was transfected into AtT-20cells.

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Expression Dexamethasone and Regulation

Juan Capistrano,CA). Peptide concentrations inmedia are expressed as picograms of peptide per microgram of total cellular protein, mean & S.E. Student's t test was performed using RS1 (Bolt, Beranek, and Newman, Cambridge, MA). DNA Filter (Southern) Blot Hybridization Analysis-Bacteriophage, plasmid, or genomic DNA isolated from AtT-20cells (17) was subjected to restriction endonuclease digestion followed by electrophoresis on 0.8% agarose gels (18)and transfer tonitrocellulose (19). Filters were hybridized overnight,either to radioactivelylabeled hCRH 1 at 52 'C or to radioactively labeled hCRH 3 a t 42 "C, and washed four times for 15 min at each the temperatureof hybridization. Genomic Southern blots had a final wash a t 62 "C. RNA Filter (Northern) Blot Hybridization Analysis-Total RNA wasisolated fromAtT-20 cells and human term placenta by the procedure of Chirgwin et al. (20). In the dexamethasone dose response and the dexamethasone time-course experiments, the number of cells per milliliter of guanidine thiocyanate was kept constant for each RNA preparation. RNA (20 pg/lane for AtT-20 cell lines, except for POMC Northern blot analysis when 0.25 pg/lane was used, and 10 pg/lane for human placental RNA) was separated on 1.4% formaldehyde agarose gels, subjected to Northern blot analysis, and transferred to nitrocellulose (19). Filters were hybridized at 65"C for 48 h (13) to 1-10 million cpm of the appropriate riboprobe. Filters were washed at 65 "C in several changes of 0.1% sodium dodecyl sulfate, 15 mM NaC1, 1.5 mM sodium citrate and exposed to x-ray film. The intensity of a mRNA band on the autoradiograph was measured by densitometry using a Joyce Loebl Chromoscan 3 densitometer (21). A Bio-Rad Model 620 videodensitometer witha Hewlett Packard 3392 integrator was used to measure by reflectometry the 18 S RNA bands ona photograph of the ethidium bromide-stainedformaldehyde gel. The concentration of 18 S RNA was used as an indicationof the amount of total RNA loaded, anddensitometrymeasurements of hCRH mRNA and neo mRNA were corrected appropriately. Filters for POMC mRNA detection were initially probed for actin mRNA. Actin mRNAdensitometrymeasurements wereused tocorrect POMC mRNA measurements for differences in the amount of total RNA loaded. RESULTS

Isolation of the Human Corticotropin-releasing Hormone Gene-One of 2 x lo5plaques from the human fetal liver X

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Charon 4A genomic library hybridized to botholigonucleotide probes, hCRH 1 and hCRH 2 complementary to the 5' and 3' portions of the 41-amino acid CRH peptide, respectively (Fig. 1). Bacteriophage DNA purified from this plaque contained an 8-kb EcoRI insert. Southern blot, restriction enzyme, and partial DNA sequence analyses of this 8-kb fragment gave results consistent with the previously published map of the human CRHgene (8) and indicated that the 8-kb hCRH gene fragment extended approximately 6 kilobases 5' to the initiator methionine and approximately 800 bases 3' to the terminationcodon of the hCRH gene. Transfection of AtT-20 Cell Linewith the Human CRH Gene--2 pg of pRSV-neo and 20 pg of pPC-g-hCRH-1001+ (Fig. 2) were cotransfected into the mouse anterior pituitary cell line AtT-20.55 of 160 G418-resistant lineswere screened for the ability to secrete CRH into the media. 13% of these cell lines had a CRH contentin the media of greater than100 pg/ml. 10-50 pg of pSV-g-hCRH-1001+ was also transfected into AtT-20cells (Fig. 3). 272 G418-resistant strains resulting from this transfection were isolated: 2of 33 screened for CRH secreted greater than 100 pg/ml CRH into the media. Two strains, S,and S p ,arising from the transfection using pSV-ghCRH-1001+ andsix lines, RI-R6,resulting from the cotransfection of pRSV2-neo with pPC-g-hCRH-1001+ were chosen for further investigation. In addition, one of the 39 G418resistant lines obtainedfrom transfecting AtT-20 cells solely with 10 pg of pSV2-neo DNA (So)was selected for further study. Characterization of CRH-secreting Strains-hCRH secretion into the media was measured over 48 h for each of the cell lines. CRH was not detected in the media of the AtT-20 RB,Rs, or So cell line a t any time point. In other cell lines CRH was undetectable in the media at 6 h, but measurable a t 24 and 48 h. The concentration of CRH in the media rose between 24 and 48 h for each of these cell lines, during which time cell number as measured by total protein also increased. The increase in CRH in the media probably reflected a parallel increase in cell number since the ratio of CRH to total protein was similar a t 24 and 48 h for each of the cell lines (TableI), and since CRH peptide was degraded with a tmhof 6 days when incubated in completemedia exposed to AtT-20cells a t 37 "C (data not shown). By Southern blot analysis, themajority of CRH-producing strains contained an 8-kb EcoRI fragment which hybridized to 32P-labeled hCRH 3, aprobe which detects the coding region of prepro-CRH (Fig. 3). The number of copies integrated varied from roughly 50/genome to 1 or fewer copies/ TABLE I CRH secretion over time in mouse AtT-20 cells stably transfected with the human CRHgene The amountof CRH present in themedia after incubation of cells for 6,24, and 48 h as well as the concentrationof total cellular protein present after 6, 24, and 48 h is shown for each cell line. The ratio of CRH in themedia to total cellular protein after 24 and 48 h is shown in the last twocolumns. ND = not detectable.

6h FIG. 3. Southern blot analysis of EcoRI-digested genomic DNA from the parent AtT-20 cell line and the stable trans- Total Total protein protein fected cell lines So, S,, S,, R,, R,, R,,R,, R,, and R,. The protein plasmid pPC-g-hCRH-1001+ wasdigested with EcoRI restriction Pg PI: enzyme to liberate an 8-kb fragment containing the human CRH ND AtT20 36 gene. Threeconcentrations of the EcoRI-digested pPC-g-hCRHSO 24 ND 1001+ corresponding to roughly 1, 10, and 100 copies of the human SI 29 ND CRH gene per AtT-20 genome are shown in the lanes marked X I , 25 ND x I O , and ~ 1 0 0DNA . was size-fractionated on a 0.8% agarose gel, 21 ND transferred tonitrocellulose and probed with'"P-labeled hCRH cRNA R, R2 27 ND 92 probe 3 which detectedthe coding region for prepro-CRH. The ND R4 59 position of DNA size markers corresponding to 23, 9.4, 6.7, and 4.4 Rs 29 ND kb is shown on the left.

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Expression and Dexamethasone Regulation of the hCRH Gene genome and did not correlate with the level of CRH secretion into the media. For example, strain Rz which had approximately 50 copies of the CRH gene/genome,expressed the lowest amount of CRHinthe media, whereas R1,which contained approximately 10 copies of the CRHgene by Southern analysis, produced four times more CRH than RP (Table I). In several strains, multiple faint bands smaller than8 kb were detected by the hCRH cRNA probe. This suggests that there was perhaps more than one site of integration of the hCRH gene into the mouse genomic DNA (Fig. 3). Alternatively, the presence of these smaller bands could reflect the lack of a EcoRI restriction siteat one end of a CRH genomic fragment prior to the integration of CRH gene sequences into a single location in themouse genome. RNA was isolated from eachcell line and subjected to filter hybridization (Northern) blot analysis. All strains which secreted CRH into the media contained a mRNA species approximately 1700 nucleotides inlengththat hybridized to hCRH 3. This mRNA was the same size in all strains and was not present in either the AtT-20 or So strains (Fig. 4). Similar results were obtained with hCRH 4, specific for the 5’ end of hCRH mRNA, which detected a mRNA species 1700 nucleotides in length in all the CRH-producing strains but not in either the AtT-20 orSo cell lines (data shown for R1 in Fig. 4B). The hCRH mRNA productof the hCRH gene transfected into mouse AtT-20 cells has the samemobility as humanplacentalCRHmRNA (Fig. 4B).Thenon-CRHsecreting strain Rs did not contain detectable CRH mRNA (data not shown). Suppression of hCRH Gene Expression by DexamethasoneTo determine whether CRH gene expression could be regulated in theseheterologous cell lines, we attempted to suppress hCRH mRNA levels with dexamethasone (lo-‘ M for 72 h). Sostrains no hCRH mRNA was detectable In the AtT-20 and using probe hCRH 4. In the CRH-secreting cell lines, the average fall in hCRH mRNA after72 h of exposure to lo-‘ M dexamethasone was 53 f 7%. This was a significant decrease in hCRH mRNA when compared to thosecells not receiving dexamethasone (p < 0.001; Fig. 5). Similar to the change in hCRH mRNA, POMC mRNA levels fell by 53 f 8% after 72 h of dexamethasone treatment. In contrast, neomycin mRNA

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levels were largely unchanged by dexamethasone treatment. Concomitant with the dexamethasone-inducedfall in hCRH and POMC mRNA levels, CRH and ACTH peptide in the media per microgram of cellular protein fell by 50 f 16 and 37 f lo%, respectively (Fig. 6 ) . The timecourse of hCRH gene suppression was determined M dexaby treating five CRH-secreting cell lineswith methasone for 6, 24, 48, 72, and 96 h (Fig. 7). There was an insignificant fall compared to control in the average hCRH mRNA concentration after6 h of dexamethasone treatment. After 24 h of treatment, hCRH mRNA and CRH peptide

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FIG. 5. Dexamethasone regulation of hCRH and POMC mRNA. Panel A, Northern blot analysis of RNA from cell line R1 cultured either in thepresence (+) or absence (-) of dexamethasone, M, for 72 h. Filters were hybridized to either theneo cRNA probe (NEO),the hCRH 4 cRNA probe (CRH), or the POMC cRNAprobe (POMC).Asterisks denote the positions of migration of neomycin resistance gene mRNA, hCRH mRNA, and POMC mRNA. Upper and lower arrowheads denote the positions of migration of 28 S and 18 S ribosomal RNA, respectively. Panel B, dexamethasone regulation of hCRH mRNA and neomycin mRNA in mouse AtT-20 cell lines transfected with the hCRH andneomycin resistance genes. Cells were grown for 72 h withandwithouttheaddition of M dexamethasone. Total RNA was isolated, subjected to Northern blot analysis and probed as inPanel A . The amount of mRNA was determined as described under “Materials and Methods.” The ratio of the mRNA concentration in the dexamethasone-treateduersus control cells was calculated and displayed for the cell lines So, SI,Rl, R,, R4, and Rs. The mean mRNA ratios f S.E. are shown on the right.

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FIG. 4. hCRH mRNA expression in AtT-20 cells transfected with the hCRH gene. Panel A, Northern blot analysisof total RNA isolated from the parent AtT-20cell line, the pSV2-neo transfected cell line So, and six CRH-secreting cell lines, R,, Rz, R4, Rs, SI, and S,. 20 pg of total RNA was size-fractionated on a 1.4% agarose gel, FIG. 6. Dexamethasone regulation of hCRH and ACTH peptransferred t o nitrocellulose, and probed with “P-labeled probe hCRH tides. The amount of CRH and ACTH peptide secreted into the 4 which detected the 5’ end of hCRH mRNA. The positions of 28 S media over 24 h per microgram of cellular protein was measured for and 18 S RNAareshownonthe right. Panel B, Northern blot each cell linewithandwithout exposure to M dexamethasone. analysis of total RNA from human placental tissue (hPL) and the Peptide measurements were made during the last 24 h of the 72-h CRH-secreting cell line R, probed with the 5”specific probe hCRH dexamethasonetreatment.Theratio of peptideconcentrationin dexamethasone-treated versus control cells shown for each cell line 4 is shown in the left panel. In the right panel is shown total RNA from cell lines R, and AtT-20 subjected to Northern blot analysis AtT-20, So, SI, R,, R,, R4, and Rs. The mean peptide ratios 2 S.E. and probed with the3”specific probe hCRH 3. are shown on theright.

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FIG.7. Time course of dexamethasone inhibitory effect. Panel A, Northern blot analysis of total RNA isolated from cell line Rz grown in the presence (+) and absence (-) of lo” M dexamethasone for 6, 24,48,72, and 96 h. Filters were hybridized to either the hCRH4 cRNA probe (CRH),the POMC cRNA probe (POMC),or the neo cRNA probe (NEO).Panel B, time course of dexamethasone regulation of hCRH mRNA, CRH peptide, POMC mRNA, and neomycin mRNA in CRH-secreting cell lines. Cell lines SI,R,, R,, R4, and Rg were grown with and without the addition of lo-? M dexamethasone for 6, 24, 48, 72, and 96 h. Total RNA was isolated, subjected of mRNA determined as described under “Materials to Northernblot analysis, probedas in Panel A and the amount and Methods.” The ratio of the mRNA concentration in the dexamethasone-treated uersus control cells was calculated for each cell line. The mean mRNA ratios +- S.E. are shown for each time point for hCRH mRNA, POMC mRNA, and neomycin mRNA. The amount of CRH peptide secreted into the media over the last 24 h of incubation (last 6 h for the 6-h time point) per microgram of cellular protein was measured for each cell line with M dexamethasone. The ratio of CRH peptide in dexamethasone-treated uersus control and without exposure to cells was calculated for each cell line. The mean CRH peptide ratios S.E. are shown for each time point. An asterisk indicates that the value is significantly different from 1 by the Student’s t test, p < 0.05.

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FIG.8. Dexamethasone dose response. Total RNA was isolated from cell lines SI and Rz incubated for 24 h in the presence of various concentrations of dexamethasone, subjected to Northern blot analysis, and probed with either the hCRH 4 cRNA probe or the POMC cRNA probe. mRNA was quantitated as described under “Materials and Methods.” The relative amount of mRNA in the dexamethasone-treated uersus control cells was calculated. Panel A displays the effect of dexamethasone concentration on hCRH mRNA levels and Panel B displays the effect of dexamethasone concentration on POMC mRNA levels.

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concentrations were suppressed, to 0.60 k 0.12 and 0.56 f 0.05% of control, respectively. This suppression continued essentially unchanged over the next 72 h of dexamethasone exposure. POMC mRNA levels were also suppressed after 24 h, but not 6 h, of dexamethasone treatment (Fig. 7). There wasa furthergradual declinein POMCmRNA levels as dexamethasone treatmentwas continued for an additional72

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h. Neomycin mRNA levels were not influenced by dexamethasone exposure, except fora slight butsignificant fall after 96 h of dexamethasone exposure (Fig. 7). However, at the 96-h timepoint,thedexamethasone-induced decline inhCRH mRNA levels was greater than the fall in neomycin mRNA levels (p < 0.02). As shown in Fig. 8A, dexamethasone suppressed hCRH


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processed inthis setting. mRNA levels in a dose-dependent fashion. The half-maximal transcribed, translated, and correctly We wished to determine whether those cis-acting elements effect on hCRH was -lo-’ M dexamethasone. POMC mRNA levels were also suppressed ina dose-dependent fashion with governing hormonal regulation of the hCRH gene were funcgene transfectedintoAtT-20 cells. the half-maximal effect occurring at -5 X lo-’ M dexameth- tioninginthehCRH asone (Fig. 8B). The latter result is in good agreement with Studies examining the regulation of CRH peptide by dexaprevious studies on dexamethasone regulationof POMC gene methasone using either immunocytochemical (32) or radioimmunoassay (33) techniques have suggested that the CRH expression in AtT-20 cells (22, 23). gene may be negativelyregulated by dexamethasone. ConDISCUSSION firming previous reports (23, 34), we found that dexamethaThe regulation of CRH gene expression is poorly under- sone treatment suppressed expressionof endogenous ACTH stood partly due to a lack of a suitable in vitro system for and POMC mRNA in AtT-20 cells. In addition, dexamethastudying its expression. T o address this problem we have sone causeda specific suppression of expression of the human isolated an 8-kb DNA fragment containing the human gene CRH gene in allof the CRH-secretingcell lines. hCRH mRNA encoding CRH, introduced it intomouse the anterior pituitary levels, as well as CRH peptide levels in the media, fell apM dexamethasone for cell line AtT-20, and have established for the first time a proximately50%afterexposureto continuous cell line capable of accurately expressing the hu- 72 h. Similar levels of hCRH gene suppression were achieved man CRH gene. This 8-kb DNA fragment contains 6 kb of after only 24 h of dexamethasone exposure and with physiosequence 5’ and0.8 kb of sequence 3’ to the region encoding logical levels of glucocorticoid. The timenecessary to achieve glucocorticoid suppression was similar to that observed for hCRH mRNA. Thus,this genomic hCRHfragmentmost of time likely contains allof the necessary 5”regulatory elements and POMC gene regulation (22), aswell as to the amount required for steroid inductionof a variety of other genes (35). 3’-transcriptionterminationand polyadenylationsignals In contrast, neomycin mRNA levels remained fairly con(24). We chose to introduce the hCRH gene into the AtT-20cell stant after dexamethasone treatment. Since neomycin gene expression was under the control of the Rous sarcoma virus line forseveral reasons.AtT-20 cells normallysynthesize, store, and secrete the peptide ACTH in a regulated fashion promoter in some cell lines and theSV40 promoter in others, this result implies, as has beenproposed previously (36), that (25). DNA encoding a number of different endocrine hormones, including the human proenkephalin gene (15), the these promoters are not sensitive to dexamethasone regularesponse of hCRHand human proinsulin cDNA (26), and the human growth hor- tion.Inaddition,thedifferential mone gene (27) has been introduced into the AtT-20 cell line. neomycin gene expression to dexamethasone treatment sugAll of these endocrine genes are accurately expressed in AtT- gests that the suppressionof hCRH gene expression was due 20 cells, and their peptide products are correctly processed not to a generalized toxic effect of dexamethasone on gene cell, but rather to a specific influence and released in a regulated fashion (28). Thus,we felt that it expression in the AtT-20 the was likelythat thiscell line would accurately express the CRHof dexamethasone on the CRH promoter. Thus, cis-acting gene. In addition, glucocorticoids are capable of negatively elements governing steroid regulation of the hCRH gene are functioning in the hCRH gene transfected into AtT-20cells. regulating pro-opiomelanocortin gene expression in AtT-20 We have introduced the humangene for CRH into a mouse cells (22, 23). Gene expression in AtT-20 cells can also be stimulated by either the cyclic AMP-dependent (29) or ino- anterior pituitary cell line and for the first time have establisheda continuous cell line that accuratelyexpresses the sitol triphosphate-diacylglycerol (30)pathways.Thus,the introduction of the hCRHgene into AtT-20cells should allow hCRH gene. The ability of some of these cell lines to secrete the opportunity to study theinfluence of these three regula- up toa nanogram of CRH permilliliter of media will be useful in future studies looking at the bioactivity of CRH and anatory systems on hCRH gene expression. The human CRH gene was introduced into mouse AtT-20 logs. We have also demonstrated that CRH gene expression cells by either cotransfection of a plasmid consisting of only is directly suppressed by dexamethasone, making this one of a small group of geneswhich are negativelyregulated by the hCRH gene and pUC-13 DNA along with the plasmid pRSV-neo orby transfection witha singleplasmid containing glucocorticoid. Thus, we have an excellent system for invespSV2-neoandthehCRH gene. Stabletransfectants were tigating those factors which confer negative gene regulation for investigatingother identified by G418 selection and screened for the ability to by glucocorticoid and,inaddition, of CRH gene expression. secrete CRH into the media. In some cell lines there may potential enhancers and suppressors have been multiple sites of integration of the hCRHgene into the host genome, rather than a single integration site as had Acknowledgments-We thank J. Toxey and M. Fiandaca for techbeen reported previously with this method of gene transfer nical assistance, T. Maniatis for the human genomic library, I. (31). In addition, the amount of CRH secreted into themedia Richardson for AtT-20/D16V cells, M. Comb forplasmid pMKSU16, was unrelated to the number of intact hCRH gene copies R. Prattfor plasmids pSV2-neo and RSV-neo, G. Gryan forsynthetic incorporated into the AtT-20genome, as has been described oligonucleotides, and M. Jacobs for excellent secretarial assistance. previously withsimilarstudiesusingtheenkephalin gene (15). REFERENCES Several criteria suggest that the hCRH gene is expressed accurately in these cell lines. All of the CRH-secreting cell 1. Vale, W., Spiess, J., Rivier, C., and Rivier, J. (1981) Science 213, lines containeda mRNA species which hybridizedto both 5’1394-1397 and3”directedCRHprobes, suggesting thatthemRNA 2. Arbiser, J., Morton, C., Bruns, G., and Majzoub, J. (1987) Cytotranscripts generated in these cell lines were full length. In genet. Cell Genet., in press 3. Benton, W. D., and Davis, R. W. (1977) Science 196, 180-182 addition, the hCRH mRNA in thesecell lines had a mobility on Northern blots that was identical to thatof hCRH mRNA 4. Caruthers, M., Beaucage, S., Efcavitch, J., Fisher, E., Matteucci, M., and Stabinsky, Y.(1980) Nucleic Acids Symp. 7,215-223 produced in the human placenta. The ability to detect the 5. Wallace, R. B., Johnson, M., Hirose, T., Miyake, T., Kawashima, secreted CRH peptide in media by radioimmunoassay also E., and Itakura, K. (1979) Nucleic Acids Res. 6,3543-3557 suggests that thegene was being expressed accurately in these 6. Majzoub, J. A., Rich, A., van Boom, J., and Habener, J. F. (1983) cell lines. These datasuggest that the hCRH gene is accurately J. Biol. Chem. 258, 14061-14064

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7. Maniatis, T., Fritsch, E., and Sambrook, J. (1982) Molecular Cloning, A Laboratory Manual, pp. 98-106, Cold Spring Harbor Laboratory, Cold Spring Harbor, NY 8. Shibahara, S., Morimoto, Y., Furutani, Y., Notake, M., Takahashi, H., Shimizu, s., Horikawa, s., and Numa, S. (1983) EMBO J. 2,775-779 9. Messing, J. (1983) Methods Enzymol. 1 0 1 , 20-77 10. Southern, P., and Berg, P. (1982) J.Mol. Appl. Genet. 1,327-341 11. Uhler, M., and Herbert, E. (1983) J.Biol. Chem. 258, 257-261 12. Birnboim, H. C., and Doly, J. (1979) Nucleic Acids Res. 7 , 15131523 13. Melton, D. A., Krieg, P. A., Rebagliati, M. R., Maniatis, T., Zinn, K., and Green, M. R. (1984) Nucleic Acids Res. 12,7035-7056 14. Graham, F. L., and van der Eb, A. J. (1973) Virology 5 2 , 456467 15.Comb,M., Liston, D., Martin, M., Rosen, H., and Herbert, E. (1985) EMBO J. 4, 3115-3122 16. Gorman, C., Padmanabhan, R., and Howard, B. (1983) Science 221,551-553 17. Maniatis, T., Fritsch, E., and Sambrook, J. (1982) Molecular Cloning, A Laboratory Manual, pp. 280-281, Cold Spring Harbor Laboratory, Cold Spring, NY 18. Southern, E. (1979) Methods Enzymol. 68, 152-176 19. Thomas, P. S. (1980) Proc. Natl. Acud. Sci. U. S. A. 7 7 , 52015205 20. Chirgwin, J. M., Przybyla, A. E., MacDonald, R. J., and Rutter, W. J. (1979) Biochemistry 1 8 , 5294-5299 21. Majzoub, J., Carrazana, E., Shulman, J., and Emanuel, R. (1987) Am. J. Physwl. 252, E637-E642

ofhCRH the Gene 22. Roberts, J. L., Budarf, M. L., Baxter, J . D., and Herbert, E. (1979) Biochemistry 18,4907-4915 23. Nakamura, M., Nakanishi, S., Sueoka, S., Imura, H., and Numa, S. (1978) Eur. J. Biochem. 86, 61-66 24. Chambon, P., Dierich, A., Gaub, M., Jakowlev, S., Jongstra, J., Krust, A., LePennec, J., Oudet, P., and Reudelhuber, T. (1984) Rec. Prog. Horm. Res. 40, 1-39 25. Affolter, H.-U, and Reisine, T. (1985)J.Biol. Chem. 260, 1547715481 26. Moore, H.-P. H., Walker, M. D., Lee, F., and Kelly, R. B. (1983) Cell 35,531-538 27. Moore, H., and Kelly, R. (1986) Nature 321,443-446 28. Kelly, R. (1985) Science 230, 25-32 29. Reisine, T., Rougon, G., and Barbet, J. (1986) J. Cell Biol. 102, 1630-1637 30. Luini, A., Lewis, D., Guild, S., Corda, D., and Axelrod, J. (1985) Proc. Natl. Acud. Sci. U. S. A. 82, 8034-8038 31. Robins, D., Ripley, S., Henderson, A., and Axel,R. (1981) Cell 23,29-39 32. Sawchenko, P., Swanson, L., and Vale,W. (1984) Proc. Natl. Acud. Sci. U. S. A. 81, 1883-1887 33. Suda, T., Tomori, N., Tozawa, F., Mouri, T., Demura, H., and Shizume, K. (1985) Life Sci. 3 7 , 1499-1505 34. Herbert, E., Allen, R. G., and Paquette, T. L. (1978) Endocrinology 1 0 2 , 218-226 35. Palmiter, R. D.,Moore, P. B., Mulvihill, E. R., and Emtage, S. (1976) Cell 8 , 557-572 36. Camper, S. A., Yao, Y. A. S., and Rottman, F. M. (1985) J. Biol. Chem. 260, 12246-12251