Polypeptide hormone regulation of gene transcription: specific 5' genomic sequences are required for epidermal growth factor and phorbol ester regulation of prolactin gene expression

PMA induces expression from the herpes simplex virus thymidine kinase promoter via the activation of JNK and ERK in the presence of adenoviral E1A proteins

The herpes simplex virus type 1 (HSV-1) thymidine kinase (TK) promoter contains elements involved in both constitutive and induced expression. We determined that phorbol 12-myristate 13-acetate (PMA) induces the HSV-1 TK promoter in HEK293 cells. However, PMA did not induce expression from the promoter in HeLa cells and did not result in a globally increased gene expression in HEK293 cells. Induction of HSV-1 TK promoter required activation of both of JNK and ERK pathways. However, activation of the two pathways alone was not sufficient for induction of HSV-1 TK promoter. By transiently transfecting into HeLa cells the adenoviral E1A gene, which exists as an integrant in HEK293 genome, we demonstrated that E1A proteins are necessary for induction of HSV-1 TK promoter by PMA. We propose mechanisms by which signaling pathways activated by the tumor-promoter PMA cooperate with the oncogene E1A to stimulate a eukaryotic promoter, namely the HSV-1 TK promoter.

Identification of a region on the adenovirus E1A gene responsible for induction by phorbol ester tumor promoter

12-O-Tetradecanoylphorbol-13-acetate (TPA) treatment induces human adenovirus (Ad) early region 1A (E1A) messenger ribonucleic acid expression in infected or Ad-transformed cells. Here, we report that deletion analysis has identified a TPA-responsive element (TRE) in the E1A enhancer region. Deletion analysis indicates that the TRE is located upstream of the E1A cap site between nucleotides -237 and -47. Incubation of extracts from TPA-treated cells with radioactively labeled deoxyribonucleic acid (DNA) fragments containing the TRE (-237 to -47) form specific DNA-protein complexes as demonstrated by gel shift analysis and Southwestern blotting. These experiments provide evidence that novel protein-DNA complexes are formed on a region of the E1A promoter required for TPA-enhanced expression. We speculate that these DNA-binding proteins may interact with the TRE and play a critical role in the mechanism through which TPA upregulates transcription from the Ad E1A gene.

Molecular cloning of the chicken prolactin gene and activation by Pit-1 and cAMP-induced factor in GH3 cells

Transcription of the prolactin (PRL) gene has been reported to be activated by a nuclear factor, Pit-1. However, the precise molecular mechanisms of the Pit-1-mediated PRL gene activation are still unclear. We have cloned the chicken PRL (cPRL) gene and its 5'-flanking region to analyze their structure and transcription-initiating mechanism. In luciferase assay, forskolin activated the proximal promoter region between -248 and -76 to transcribe the cPRL gene in GH3 cells, although there is no canonical cyclic AMP-responsive element in the promoter region. In gel mobility shift assay, a DNA fragment between -104 and -76 containing a putative Pit-1 binding site was bound by nuclear factors from the GH3 cells. Furthermore, it was observed that Pit-1 protein specifically bound to the DNA fragment in the supershift assay. These results indicate that both Pit-1 and cAMP-induced factor(s) associated with the cis element on the proximal promoter region to activate cPRL gene expression in GH3 cells.

A role for the mitogen-activated protein kinase in mediating the ability of thyrotropin-releasing hormone to stimulate the prolactin promoter

The hypothalamic hormone, TRH, stimulates PRL secretion and gene transcription. We have examined the possibility that the mitogen-activated protein kinase (MAPK) may play a role in mediating TRH effects on the PRL gene. TRH was found to stimulate sustained activation of MAPK in PRL-producing, GH3 cells, consistent with a possible role in transcriptional regulation. A kinase-defective, interfering MAPK kinase (MAPKK) mutant reduced TRH induction of the PRL promoter. Treatment with the MAPKK inhibitor, PD98059, blocked TRH-induced activation of MAPK and also reduced TRH induction of a PRL-luciferase reporter gene, confirming that MAPK activation is necessary for TRH effects on PRL gene expression. Previous studies have demonstrated that the PRL promoter contains binding sites for members of the Ets family of transcription factors, which are important for mediating MAPK responsiveness of the PRL promoter. Mutation of specific Ets sites within the PRL promoter reduced responsiveness to both TRH and MAPK. The finding that DNA elements required for MAPK responsiveness of the PRL gene colocalize with DNA elements required for TRH responsiveness further supports a role for MAPK in mediating TRH effects on the PRL gene. We also explored the signaling mechanisms that link the TRH receptor to MAPK induction. Occupancy of the TRH receptor results in activation of protein kinase C (PKC) as well as increases in the concentration of Ca2+ due to release from intracellular stores and entry of Ca2+ through Ca2+ channels. A PKC inhibitor, GF109203X, and an L-type Ca2+ channel blocker, nimodipine, both partially reduced TRH-induced MAPK activation and PRL promoter activity. The effects of the two inhibitors were additive. These studies are consistent with a signaling pathway involving PKC- and Ca2+-dependent activation of MAPK, which leads to phosphorylation of an Ets transcription factor and activation of the PRL promoter.

Stimulation of the preprothyrotropin-releasing hormone gene by epidermal growth factor

Regulation of the expression of the prepro-TRH (ppTRH) gene by epidermal growth factor (EGF) was investigated. The i.p. injection of EGF significantly stimulated hypothalamic ppTRH messenger RNA levels in rats. To clarify whether this stimulatory effect of EGF could be exerted at the level of gene transcription, the 5'-flanking region (-1893/+127) of the mouse ppTRH gene fused to a luciferase reporter gene was transiently transfected into pituitary GH4C1 cells, and the effect of EGF on gene transcription was measured by a luciferase assay. EGF stimulated ppTRH gene promoter activity in a time- and dose-dependent manner. Deletion analysis revealed that two different regions of the promoter, between -254 and -218 [EGF response element-1 (EGFRE1)] and between -130 and -84 (EGFRE2) were required for full stimulation by EGF. The two EGFREs possessed putative binding sequences for the transcription factor Sp1, and they functioned cooperatively in heterologous promoters. Nuclear extracts from GH4C1 cells specifically bound those two EGFREs in gel retardation assays. Two protein-DNA complexes were found on EGFRE1, whereas four complexes were observed on EGFRE2. Although the binding of nuclear extracts to EGFRE1 was competed for by the consensus Sp1 binding sequence, the complexes on EGFRE1 were not supershifted by an Sp1 antibody. Formation of the slower migrating protein complex on EGFRE1 was prevented by EDTA, suggesting that one of the EGFRE1-binding proteins might be an Sp1-related zinc finger protein. Competition and supershift experiments demonstrated that the EGFRE2-binding protein showing that the slowest migration possessed a characteristic similar to that of Sp1. Selective mutations of the Sp1-binding site in EGFRE2 markedly diminished the EGF-induced stimulation. These results suggest that EGF may function as a positive regulator of ppTRH gene expression, and that the stimulatory effect may be mediated through a cooperative interaction between Sp1 or Sp1-related proteins and additional factors that bind to two separate DNA regions.

Pituitary cytokine and growth factor expression and action

The complex range of pituitary regulatory mechanisms reviewed here underlies the critical function of the pituitary in sustaining all higher life forms. Thus, the ultimate net secretion of pituitary hormones is determined by signal integration from all three tiers of pituitary control. It is clear from our current knowledge that the trophic hormone cells of the anterior pituitary are uniquely specialized to respond to these signals. Unravelling their diversity and complexity will shed light upon the normal function of the master gland. Understanding these control mechanisms will lead to novel diagnosis and therapy of disordered pituitary function (357).

Heparin-binding secretory transforming gene (hst) facilitates rat lactotrope cell tumorigenesis and induces prolactin gene transcription

We have shown previously that human prolactinomas express transforming sequences of the heparin-binding secretory transforming gene (hst) which encodes fibroblast growth factor-4 (FGF-4). To elucidate the role of hst in pituitary tumorigenesis we treated primary rat pituitary and pituitary tumor cell cultures with recombinant FGF-4 and also stably transfected pituitary cell lines with full-length human hst cDNA. Transfectants were screened for hst mRNA expression and FGF-4 production. FGF-4 (0.1-50 ng/ml) caused a dose-dependent 2.5-fold increase of prolactin (PRL) secretion (P < 0.001) in GH4 cells and up to 60% (P < 0.05) in primary cultures, while decreasing growth hormone release (P < 0.001). GH4 hst transfectants displayed markedly enhanced basal PRL secretion (threefold, P < 0.001) and also proliferated faster (P < 0.001). FGF-4 treatment of wild-type GH4 cells, transiently transfected with an expression construct (rPRL.luc) containing a luciferase reporter driven by the rPRL promoter, resulted in a dose-dependent increase of up to 3.3-fold in PRL transcriptional activity. Tumors derived from in vivo subcutaneous injection of GH4 hst-transfected cells strongly expressing FGF-4 grew more aggressively as assessed by histologic invasiveness and proliferating cell nuclear antigen staining (P < 0.01). The results indicate that hst overexpression mediates lactotrope tumor growth and potently stimulates PRL synthesis. Thus, hst may directly facilitate prolactinoma development via paracrine or autocrine action of its secreted protein, FGF-4.

A composite Ets/Pit-1 binding site in the prolactin gene can mediate transcriptional responses to multiple signal transduction pathways

Binding sites for the tissue-specific transcription factor, Pit-1, are required for basal and hormonally induced prolactin gene transcription. Although Pit-1 is phosphorylated in response to several signaling pathways, the mechanism by which Pit-1 contributes to hormonal induction of gene transcription has not been defined. Recent reports suggest that phosphorylation of Pit-1 may not be required for hormonal regulation of the prolactin promoter. Analysis of the contribution of individual Pit-1 binding sites has been complicated due to the fact that some of the elements appear to be redundant. To better understand the role of Pit-1 sites in mediating hormonal regulation of the prolactin gene, we have performed enhancer tests using the three most proximal Pit-1 binding sites of the rat prolactin gene which are designated the 1P, 2P, and 3P sites. The results demonstrate that multimers of the 3P Pit-1 binding site are much more responsive to several hormonal and intracellular signaling pathways than multimers of the 1P or 2P sites. The 3P DNA element was found to contain a consensus binding site for the Ets family of proteins. Mutation of the Ets binding site greatly decreased the ability of epidermal growth factor, phorbol esters, Ras, or the Raf kinase to induce reporter gene activity. Mutation of the Ets site had little effect on basal enhancer activity. In contrast, mutation of the consensus Pit-1 binding site in the 3P element essentially abolished all basal enhancer activity. Overexpression of Ets-1 in GH3 pituitary cells enhanced both basal and Ras induced activity from the 3P enhancer. These data describe a composite element in the prolactin gene containing binding sites for two different factors and the studies suggest a mechanism by which Ets proteins and Pit-1 functionally cooperate to permit transcriptional regulation by different signaling pathways.

Interaction between transcription regulatory regions of prolactin chromatin

The regulation of transcription requires complex interactions between proteins bound to DNA sequences that are often separated by hundreds of base pairs. As demonstrated by a nuclear ligation assay, the distal enhancer and the proximal promoter regions of the rat prolactin gene were found to be juxtaposed. By acting through its receptor bound to the distal enhancer, estrogen stimulated the interaction between the distal and proximal regulatory regions two- to threefold compared to control values. Thus, the chromatin structure of the prolactin gene may facilitate the occurrence of protein-protein interactions between transcription factors bound to widely separated regulatory elements.

Control of prolactin secretion

1. Prolactin is a 21,500 Dalton single-chain polypeptide hormone but may occur in 50 kDa and 150 kDa molecular variants. 2. These large PRL variants may be secreted predominantly; this condition is termed "macroprolactinemia". It is characterized by high immunological and normal biological serum levels of prolactin, and lack of clinical symptoms of hyperprolactinemia. 3. The information on PRL is encoded on chromosome 6. Transcription can be enhanced and suppressed by a variety of hormonal factors. 4. PRL is secreted in a pulsatile fashion; it displays a circadian rhythm (with a maximum during sleep) and is stimulated by some amino acids. PRL also responds to mechanical stimulation of the breast. 5. PRL rises during pregnancy, and maintainance of hyperprolactinemia (and, thereby, physiological infertility) is dependent on the frequency and duration of breast feedings. 6. Hypothalamic regulation of prolactin mainly involves tonic inhibition via portal dopamine. The physiological importance of various stimulating factors present in the hypothalamus is still incompletely understood. In particular, there is still no place for TRH in PRL physiology. 7. PRL is released in response to stress; this response may be mediated by opioids. The low-estrogen, low-gonadotropin amenorrhea of endurance-training women is not mediated by prolactin, however. 8. Estrogens stimulate PRL gene transcription via at least two independent mechanisms. There are many clinical examples of this estrogen effect on prolactin serum levels, and also on the growth of prolactinomas. 9. Mild hyperprolactinemia remains an enigma which cannot satisfactorily be resolved by biochemical or radiological testing. The border between "normal" and "elevated" prolactin is ill-defined. The possibility of macroprolactinemia complicates this matter even further. 10. The number of drugs which suppress prolactin by acting on pituitary D2 receptors, and which are useful in the treatment of hyperprolactinemia, continues to increase. In the field of ergot alkaloids, parenteral application appears to be a logical solution to the problem of the high first-pass effect; in addition, this form of treatment is frequently better tolerated than the oral route. 11. Prolactinoma development is presently being studied employing molecular biological techniques; the question of whether tumorigenesis can be attributed to specific defects of gene regulation remains to be answered.

Identification of a distal regulatory element in the 5' flanking region of the bovine prolactin gene

The 5'-flanking region of the bovine prolactin gene was cloned and sequenced. The expression of chimeric gene constructs containing 5'-flanking DNA fragments from the prolactin gene joined to a reporter gene encoding human growth hormone (hGH) was examined using transiently transfected rat pituitary cells. Prolactin nucleotide sequences located at position -1213 to -925 enhance the basal level of expression of growth hormone by 5-fold and function in a position- and orientation-independent fashion. In addition to increasing the basal level of growth hormone expression, this enhancer element also responds to induction by epidermal growth factor. The nucleotide sequence of the bovine prolactin gene enhancer element is highly similar to an enhancer element located approximately -1.5 kb from the rat prolactin transcription initiation site. Deletion analysis of the enhancer region shows that sequences -1124 to -985 are necessary and sufficient for enhancer activity.

The calcitonin gene peptides: biology and clinical relevance

The calcitonin/CGRP multigene complex encodes a family of peptides: calcitonin, its C-terminal flanking peptide, katacalcin, and a third novel peptide, calcitonin gene-related peptide (CGRP). The 32-amino acid peptide calcitonin inhibits the osteoclast, thereby conserving skeletal mass during periods of potential calcium lack, such as pregnancy, growth, and lactation. This hormonal role is emphasized by observations that lower circulating calcitonin levels are associated with bone loss and that calcitonin replacement prevents further bone loss. Structurally, CGRP resembles calcitonin and has been implicated in neuromodulation and in the physiological regulation of blood flow. Here we review the molecular genetics, structure, and function of the calcitonin-gene peptides as analyzed in the laboratory and focus on more recent clinical studies relating to disorders and therapeutics.

Prolactin upstream factor I mediates cell-specific transcription

DNA sequence-specific chromatography was used to purify prolactin upstream factor I (PUF-I) approximately 10,000- to 20,000-fold from rat GH3 cells. The purified transcription factor reconstituted enhanced pituitary-specific prolactin RNA synthesis in nonpituitary in vitro transcription assays. In vitro mutagenesis demonstrated that the capacity to stimulate prolactin gene transcription was directly correlated with PUF-I binding to an A+T-rich region located from -63 to -36 in the prolactin 5'-flanking DNA. We propose that PUF-I is a critical modulator of transcriptional activity in pituitary cells and has a central role in the stimulation of prolactin gene transcription in the mammalian pituitary lactotroph.

Regulation of the gastrin promoter by epidermal growth factor and neuropeptides

The regulation of gastrin gene transcription was studied in GH4 pituitary cells transfected with constructs comprised of the first exon of the human gastrin gene and various lengths of 5' regulatory sequences ligated upstream of the reporter gene chloramphenicol acetyltransferase. Gastrin reporter gene activity in GH4 cells was equal to the activity of a reporter gene transcribed from the endogenously expressed growth hormone promoter. The effect of a variety of peptides on gastrin gene transcription including epidermal growth factor (normally present in the gastric lumen), gastrin-releasing peptide, vasoactive intestinal peptide, and somatostatin (present in gastric nerves) was assessed. Epidermal growth factor increased the rate of gastrin transcription almost 3-fold, whereas thyrotropin-releasing hormone and vasoactive intestinal peptide increased gastrin transcription 2- and 1.5-fold, respectively. Gastrin-releasing peptide, a peptide that strongly stimulates gastrin release, weakly increased gastrin transcription (1.3-fold). Somatostatin inhibited the increase in gastrin transcription induced by epidermal growth factor, thyrotropin-releasing hormone, and vasoactive intestinal peptide. Constructs containing various lengths of 5' regulatory sequences defined a response element -40 to -82 base pairs (bp) 5' to the transcription initiation site. This 40-bp sequence contains Sp1 and AP2 binding sites, which suggests that epidermal growth factor and thyrotropin-releasing hormone stimulate gastrin gene transcription through transcription factors that bind to Sp1 and/or AP2 motifs.

Activity-dependent regulation of gene expression in muscle and neuronal cells

In both the central and the peripheral nervous systems, impulse activity regulates the expression of a vast number of genes that code for synaptic proteins, including neuropeptides, enzymes involved in neurotransmitter biosynthesis and degradation, and membrane receptors. In recent years, the mechanisms involved in these regulations became amenable to investigation by the methods of recombinant DNA technology. The first part of this review focuses on the activity-dependent control of nicotinic acetylcholine receptor biosynthesis in vertebrate muscle, a model case for the regulation of synaptic protein biosynthesis at the postsynaptic level. The second part summarizes some examples of neuronal proteins whose biosynthesis is under the control of transsynaptic impulse activity. The first, second, and third intracellular messengers involved in membrane-to-gene signaling are discussed, as are possible posttranscriptional control mechanisms. Finally, models are proposed for a role of neuronal activity in the genesis and stabilization of the synapse.

The NF-kappa B-binding site mediates phorbol ester-inducible transcription in nonlymphoid cells

The mouse immunoglobulin kappa light-chain enhancer can interact with at least three independent nuclear proteins. One of these proteins, NF-kappa B, is constitutively present only in nuclear extracts derived from B cells and plasma cells. A DNA-binding protein with the same sequence specificity (and therefore presumed to be NF-kappa B itself) can be induced in pre-B cells, T cells, and nonlymphoid cells by phorbol 12-acetate-13-myristate (PMA); however, it is not clear whether the induced factor can activate transcription in nonlymphoid cells as NF-kappa B does in B cells. In this paper we show that multimerization of a fragment of the mouse kappa enhancer that carried only the binding site for NF-kappa B behaved like a B-cell-specific regulatory element. Furthermore, this unit served to activate transcription in nonlymphoid cells after treatment with PMA (but not with cyclic AMP derivatives), and the kinetics of transcription activation correlated well with the kinetics of factor induction. Thus, the induced DNA-binding activity appeared to be functionally indistinguishable from that of NF-kappa B.

Prolactin upstream factor I mediates cell-specific transcription

DNA sequence-specific chromatography was used to purify prolactin upstream factor I (PUF-I) approximately 10,000- to 20,000-fold from rat GH3 cells. The purified transcription factor reconstituted enhanced pituitary-specific prolactin RNA synthesis in nonpituitary in vitro transcription assays. In vitro mutagenesis demonstrated that the capacity to stimulate prolactin gene transcription was directly correlated with PUF-I binding to an A+T-rich region located from -63 to -36 in the prolactin 5'-flanking DNA. We propose that PUF-I is a critical modulator of transcriptional activity in pituitary cells and has a central role in the stimulation of prolactin gene transcription in the mammalian pituitary lactotroph.

The NF-kappa B-binding site mediates phorbol ester-inducible transcription in nonlymphoid cells

The mouse immunoglobulin kappa light-chain enhancer can interact with at least three independent nuclear proteins. One of these proteins, NF-kappa B, is constitutively present only in nuclear extracts derived from B cells and plasma cells. A DNA-binding protein with the same sequence specificity (and therefore presumed to be NF-kappa B itself) can be induced in pre-B cells, T cells, and nonlymphoid cells by phorbol 12-acetate-13-myristate (PMA); however, it is not clear whether the induced factor can activate transcription in nonlymphoid cells as NF-kappa B does in B cells. In this paper we show that multimerization of a fragment of the mouse kappa enhancer that carried only the binding site for NF-kappa B behaved like a B-cell-specific regulatory element. Furthermore, this unit served to activate transcription in nonlymphoid cells after treatment with PMA (but not with cyclic AMP derivatives), and the kinetics of transcription activation correlated well with the kinetics of factor induction. Thus, the induced DNA-binding activity appeared to be functionally indistinguishable from that of NF-kappa B.

Reconstitution of cell-type-specific transcription of the rat prolactin gene in vitro

We present evidence for the existence of prolactin upstream factor 1 (PUF-1) in rat pituitary-derived cells and demonstrate its interaction with a symmetrical DNA element located in the 5' flanking region of the gene. An in vitro expression system developed from pituitary-derived GH3 cells was used to determine that 420 base pairs (bp) of 5' flanking DNA was sufficient for cell-specific, accurate, and efficient RNA polymerase II transcription of the rat prolactin gene. Reconstitution of in vitro transcription with pituitary and nonpituitary nuclear extracts suggested that the presence of GH3 cell-specific factors mediated the activation of prolactin gene expression. We also demonstrated that a functionally stable transcription complex assembled on the prolactin promoter. Using DNase I protection procedures, we have identified the DNA-protein binding area in the prolactin 5' flanking region. GH3 nuclear extracts contain a cell-specific protein (PUF-I) that binds to a 28-bp region (-63 to -36)which contains an 18-bp imperfect palindrome (-63 to -46). The role that the interaction between PUF-I and the imperfect palindrome plays in in vitro pituitary-specific prolactin gene expression is discussed.

Molecular cloning of gene sequences regulated by tumor promoters and mitogens through protein kinase C

cDNA clones representing genes whose expression is modulated by treatment with mitogens and tumor promoters were isolated and characterized. TPA-S1 corresponds to an mRNA species whose abundance was increased markedly within 1 h of exposure to the tumor promoter 12-O-tetradecanoyl phorbol-13-acetate (TPA), and TPA-R1 represents an mRNA that was decreased in TPA-treated cells. The induction of TPA-S1 was blocked by actinomycin D but was not affected by cycloheximide, and it was specific for phorbol esters with tumor-promoting activity. The role of protein kinase C in the induction of TPA-S1 is supported by the following lines of evidence. (i) Agents that activated protein kinase C (TPA, platelet-derived growth factor, and diacylglycerol) also increased TPA-S1 mRNA levels. (ii) A potent PKC inhibitor blocked the induction of TPA-S1. (iii) Down-regulation of PKC activity, by treatment of cells with TPA for 24 h, resulted in a loss of responsiveness to TPA-S1 induction by subsequent TPA treatment. DNA sequence analysis of TPA-S1 predicts a cysteine-rich, secreted protein with a molecular weight of 22.6 X 10(3) that exhibits homology with sequences representing a protein with human erythroid-potentiating activity and protease inhibitory activity.

Inducible gene expression from multiple promoters by the tumor-promoting agent, PMA

Phorbol ester tumor promoters affect a broad scope of changes in mammalian cells. This report describes the activation of expression of an introduced chloramphenicol acetyltransferase (CAT) reporter gene by the phorbol ester, phorbol 12-myristate 13-acetate (PMA), in a variety of fibroblast and hematopoietic cell lines. PMA-mediated activation appears to be promoter region specific, yet widespread. Enhanced gene expression is observed for four out of five promoter systems tested, and, in some cases, is dependent on the cellular environment. Further experiments indicate that PMA mediates elevated gene expression by rapidly increasing steady state levels of CAT mRNA. The broad range of promoters affected by PMA may help explain the high potency of this agent in tumor production.

Reconstitution of cell-type-specific transcription of the rat prolactin gene in vitro

We present evidence for the existence of prolactin upstream factor 1 (PUF-1) in rat pituitary-derived cells and demonstrate its interaction with a symmetrical DNA element located in the 5' flanking region of the gene. An in vitro expression system developed from pituitary-derived GH3 cells was used to determine that 420 base pairs (bp) of 5' flanking DNA was sufficient for cell-specific, accurate, and efficient RNA polymerase II transcription of the rat prolactin gene. Reconstitution of in vitro transcription with pituitary and nonpituitary nuclear extracts suggested that the presence of GH3 cell-specific factors mediated the activation of prolactin gene expression. We also demonstrated that a functionally stable transcription complex assembled on the prolactin promoter. Using DNase I protection procedures, we have identified the DNA-protein binding area in the prolactin 5' flanking region. GH3 nuclear extracts contain a cell-specific protein (PUF-I) that binds to a 28-bp region (-63 to -36)which contains an 18-bp imperfect palindrome (-63 to -46). The role that the interaction between PUF-I and the imperfect palindrome plays in in vitro pituitary-specific prolactin gene expression is discussed.

Molecular cloning of gene sequences regulated by tumor promoters and mitogens through protein kinase C

cDNA clones representing genes whose expression is modulated by treatment with mitogens and tumor promoters were isolated and characterized. TPA-S1 corresponds to an mRNA species whose abundance was increased markedly within 1 h of exposure to the tumor promoter 12-O-tetradecanoyl phorbol-13-acetate (TPA), and TPA-R1 represents an mRNA that was decreased in TPA-treated cells. The induction of TPA-S1 was blocked by actinomycin D but was not affected by cycloheximide, and it was specific for phorbol esters with tumor-promoting activity. The role of protein kinase C in the induction of TPA-S1 is supported by the following lines of evidence. (i) Agents that activated protein kinase C (TPA, platelet-derived growth factor, and diacylglycerol) also increased TPA-S1 mRNA levels. (ii) A potent PKC inhibitor blocked the induction of TPA-S1. (iii) Down-regulation of PKC activity, by treatment of cells with TPA for 24 h, resulted in a loss of responsiveness to TPA-S1 induction by subsequent TPA treatment. DNA sequence analysis of TPA-S1 predicts a cysteine-rich, secreted protein with a molecular weight of 22.6 X 10(3) that exhibits homology with sequences representing a protein with human erythroid-potentiating activity and protease inhibitory activity.

Thyroid hormone regulates expression of a transfected alpha-myosin heavy-chain fusion gene in fetal heart cells

In ventricular muscle, 3,5,3'-triiodo-L-thyronine (T3) stimulates the expression of the alpha-myosin heavy-chain (alpha-MHC) gene. To test for gene elements required for induction, a fragment of the alpha-MHC gene containing 2.9 kilobases of 5' flanking sequences and 420 base pairs of DNA 3' to the transcription initiation site was linked to the coding sequences of the bacterial chloramphenicol acetyltransferase (CAT) gene. The alpha-MHC fusion gene was introduced into primary cultures of fetal rat heart myocytes. Induction of the transfected gene was monitored by assaying CAT activity while endogenous alpha-MHC mRNA expression was measured by using a synthetic oligonucleotide probe complementary to sequences in the 3' untranslated region of the mRNA. Without T3, CAT activity was only slightly greater than background. When T3 at a final concentration of 10 nM was added to the cultures, CAT activity was increased 8-fold by 48 hr. The response time and doses of T3 required for induction of CAT activity and alpha-MHC mRNA in transfected cells were similar, suggesting that the synthetic and endogenous genes may have a common mechanism of control. When simian virus 40 enhancer and early promoter sequences were included in the construct, CAT activity was constitutively expressed, but it could be increased 7-fold by the addition of T3. Several deletions were introduced into the 5' flanking sequences of the alpha-MHC fragment and the effects on induction of CAT activity were examined. Progressive deletions of 5' sequences from positions -947 to -374 reduced but did not eliminate induction of CAT activity, suggesting that more than one region may be required for optimal induction by thyroid hormone. The results indicate that DNA sequences required for efficient induction by T3 are present in the 5' flanking sequences of the alpha-MHC gene.

The yeast repeated element sigma contains a hormone-inducible promoter

A genomic clone (lambda ScG7) from Saccharomyces cerevisiae encoded a 650-nucleotide poly(A)-containing [poly(A)+] RNA that was about 50 times more abundant in MATa cells that had been exposed to the peptide pheromone alpha-factor than in untreated cells. This RNA was transcribed from a cluster of repetitive sequences: both intact and truncated delta and sigma elements adjacent to a tRNATrp gene. Strand-specific probes indicated that this RNA initiated within an intact sigma element and contained sigma sequences at its 5' end. MATa cells produced two other prominent poly(A)+ RNAs (500 and 5,300 bases) in response to alpha-factor that were homologous to the same strand of sigma but transcribed from other locations in the genome. Induction of the sigma-related transcripts was rapid, was not blocked by inhibition of protein synthesis, required a functional receptor (STE2 gene product), and hence appeared to be a primary response to pheromone. Pulse-labeling confirmed that accumulation of sigma RNA following alpha-factor administration was accounted for by an increase in its rate of transcription. The sigma RNAs also were induced in MAT alpha cells that had been treated with a-factor, but were not present at significant levels in MATa/MAT alpha diploids. In MATa cells transformed with a plasmid in which the lambda ScG7 sigma element was inserted just upstream of a gene coding for the intracellular form of invertase (SUC2) lacking its own promoter, a new poly(A)+ RNA (2.2 kilobases) appeared in response to alpha-factor that hybridized to both sigma and SUC2 probes, and intracellular invertase activity was elevated about 10-fold within 30 min. Primer extension showed that transcription from the hybrid gene initiated exclusively within the sigma sequence (117 nucleotides from the 3' end of the element).

The yeast repeated element sigma contains a hormone-inducible promoter

A genomic clone (lambda ScG7) from Saccharomyces cerevisiae encoded a 650-nucleotide poly(A)-containing [poly(A)+] RNA that was about 50 times more abundant in MATa cells that had been exposed to the peptide pheromone alpha-factor than in untreated cells. This RNA was transcribed from a cluster of repetitive sequences: both intact and truncated delta and sigma elements adjacent to a tRNATrp gene. Strand-specific probes indicated that this RNA initiated within an intact sigma element and contained sigma sequences at its 5' end. MATa cells produced two other prominent poly(A)+ RNAs (500 and 5,300 bases) in response to alpha-factor that were homologous to the same strand of sigma but transcribed from other locations in the genome. Induction of the sigma-related transcripts was rapid, was not blocked by inhibition of protein synthesis, required a functional receptor (STE2 gene product), and hence appeared to be a primary response to pheromone. Pulse-labeling confirmed that accumulation of sigma RNA following alpha-factor administration was accounted for by an increase in its rate of transcription. The sigma RNAs also were induced in MAT alpha cells that had been treated with a-factor, but were not present at significant levels in MATa/MAT alpha diploids. In MATa cells transformed with a plasmid in which the lambda ScG7 sigma element was inserted just upstream of a gene coding for the intracellular form of invertase (SUC2) lacking its own promoter, a new poly(A)+ RNA (2.2 kilobases) appeared in response to alpha-factor that hybridized to both sigma and SUC2 probes, and intracellular invertase activity was elevated about 10-fold within 30 min. Primer extension showed that transcription from the hybrid gene initiated exclusively within the sigma sequence (117 nucleotides from the 3' end of the element).

Epidermal growth factor regulates the expression of its own receptor

The epidermal growth factor (EGF) receptor gene is the cellular homolog of the avian erythroblastosis virus erbB oncogene. Control of EGF receptor expression determines cellular responsiveness to EGF and might play an important role in neoplastic development. Using RNA blot hybridization, we have found that exposure of human KB carcinoma cells to EGF results in elevated levels of EGF receptor mRNA. The phorbol ester 4 beta-phorbol 12-myristate 13-acetate also stimulates EGF receptor RNA accumulation. Immunoprecipitation of metabolically labeled (30 min) EGF receptor protein revealed that synthesis of new EGF receptor follows the increase in receptor RNA. Addition of cycloheximide together with EGF further enhances EGF receptor RNA accumulation. Results of nuclear runoff-transcription experiments suggest that the stimulatory effects of EGF and cycloheximide are most likely due to a posttranscriptional control mechanism.

Ca2+ and phospholipid-dependent protein kinase activity and phosphorylation of endogenous proteins in bovine adrenal medulla

Soluble and membrane fractions of bovine adrenal medulla contain several substrates for the Ca2+/phospholipid-dependent and cyclic AMP-dependent protein kinases. The phosphorylation of soluble proteins (36 and 17.7 kilodaltons) and a membrane protein (22.5 kilodaltons) showed an absolute requirement for the presence of both Ca2+ and phosphatidylserine; other substrates showed less stringent phosphorylation requirements and many of these proteins were specific for each of the protein kinases. The Ca2+/phospholipid-dependent phosphorylation was rapid, with effects seen as early as at 30 s of incubation. Measurement of enzyme activities with histone H1 as an exogenous substrate demonstrated that the Ca2+/phospholipid-dependent protein kinase was equally distributed between the soluble and membrane fractions whereas the cyclic AMP-dependent enzyme was predominantly membrane-bound in adrenal medulla and chromaffin cells. The activity of the soluble Ca2+/phospholipid-dependent protein kinase of adrenal medulla was found to be about 50% of the enzyme level present in rat brain, a tissue previously shown to contain a very high enzyme activity. These results suggest a prominent role for the Ca2+/phospholipid-dependent protein kinase in chromaffin cell function.

Specific stimulation of actin gene transcription by epidermal growth factor and cycloheximide

Stimulation of quiescent AKR-2B mouse embryo cells with epidermal growth factor (EGF) results in a rapid and specific induction of actin mRNA sequences. These mRNAs include those coding for both beta- and gamma-cytoskeletal, but not alpha-skeletal muscle, actin isotypes. Elongation of nascent RNA chains in isolated nuclei (run-off transcription) demonstrates that the mRNA accumulation is preceded by an increase in actin gene transcription. This increase is transient, however, and is followed by a rapid attenuation of transcriptional activity. An inhibitor of protein synthesis, cycloheximide, was also found to induce beta- and gamma-actin mRNA accumulation. Furthermore, the simultaneous addition of EGF and cycloheximide produced a synergistic effect on actin sequences in both steady-state nuclear and polysomal RNA. Run-off transcription experiments demonstrate that this synergistic effect results from an increase in the magnitude and duration of actin gene transcription. It is also specific in that alpha-tubulin gene transcription is not similarly affected. These data suggest the existence of a specific labile repressor of actin gene transcription.

Expression cloning of human EGF receptor complementary DNA: gene amplification and three related messenger RNA products in A431 cells

In order to further define the mechanisms by which polypeptide growth factors regulate gene transcription and cellular growth, expression cloning techniques were used to select human epidermal growth factor (EGF) receptor complementary DNA clones. The EGF 3' coding domain shows striking homology to the transforming gene product of avian erythroblastosis virus (v-erbB). Over-expression of EGF receptors in A431 cell lines correlates with increased EGF receptor mRNA levels and amplification (up to 110 times) of the apparently singular EGF receptor gene. There appear to be three cytoplasmic polyadenylated RNA products of EGF receptor gene expression in A431 cells, one of which contains only 5' (EGF binding domain) sequences and is postulated to encode the secreted EGF receptor-related protein.