Evidence for a role of calmodulin in the regulation of prolactin gene expression

Olfactory marker protein regulates prolactin secretion and production by modulating Ca2+ and TRH signaling in lactotrophs

Olfactory marker protein (OMP) is a marker of olfactory receptor-mediated chemoreception, even outside the olfactory system. Here, we report that OMP expression in the pituitary gland plays a role in basal and thyrotropin-releasing hormone (TRH)-induced prolactin (PRL) production and secretion. We found that OMP was expressed in human and rodent pituitary glands, especially in PRL-secreting lactotrophs. OMP knockdown in GH4 rat pituitary cells increased PRL production and secretion via extracellular signal-regulated kinase (ERK)1/2 signaling. Real-time PCR analysis and the Ca²⁺ influx assay revealed that OMP was critical for TRH-induced PRL secretion. OMP-knockout mice showed lower fertility than control mice, which was associated with increased basal PRL production via activation of ERK1/2 signaling and reduced TRH-induced PRL secretion. However, both in vitro and in vivo results indicated that OMP was only required for hormone production and secretion because ERK1/2 activation failed to stimulate cell proliferation. Additionally, patients with prolactinoma lacked OMP expression in tumor tissues with hyperactivated ERK1/2 signaling. These findings indicate that OMP plays a role in PRL production and secretion in lactotrophs through the modulation of Ca²⁺ and TRH signaling.

Uncovering the regulatory mechanism behind production of the prolactin hormone may help tackle reproductive health problems. As well as triggering milk production in female mammals, prolactin is critical for healthy reproduction in both sexes. An excess of prolactin secreted by cells called lactotrophs in the pituitary gland can cause infertility. While scientists know which hormones stimulate prolactin release, how prolactin levels are regulated is unclear. Eun Jig Lee and Cheol Ryong Ku at Yonsei University in Seoul, Korea, and co-workers demonstrated that the olfactory marker protein (OMP) plays a central role in regulating prolactin production. They found that OMP specifically and highly expressed in lactotrophs. Eliminating OMP expression in mice left a key signalling pathway and calcium ion levels upregulated, resulting in increased prolactin and reduced fertility.

Modulation of calmodulin gene expression as a novel mechanism for growth hormone feedback control by insulin-like growth factor in grass carp pituitary cells

Calmodulin (CaM), the Ca2+ sensor in living cells, is essential for biological functions mediated by Ca2+-dependent mechanisms. However, modulation of CaM gene expression at the pituitary level as a means to regulate pituitary hormone synthesis has not been characterized. In this study we examined the functional role of CaM in the feedback control of GH by IGF using grass carp pituitary cells as a cell model. To establish the structural identity of CaM expressed in the grass carp, a CaM cDNA, CaM-L, was isolated from the carp pituitary using 3'/5' rapid amplification of cDNA ends. The open reading frame of this cDNA encodes a 149-amino acid protein sharing the same primary structure with CaMs reported in mammals, birds, and amphibians. This CaM cDNA is phylogenetically related to the CaM I gene family, and its transcripts are ubiquitously expressed in the grass carp. In carp pituitary cells, IGF-I and IGF-II induced CaM mRNA expression with a concurrent drop in GH transcript levels. These stimulatory effects on CaM mRNA levels were not mimicked by insulin and appeared to be a direct consequence of IGF activation of CaM gene transcription without altering CaM transcript stability. CaM antagonism and inactivation of calcineurin blocked the inhibitory effects of IGF-I and IGF-II on GH gene expression, and CaM overexpression also suppressed the 5' promoter activity of the grass carp GH gene. These results, as a whole, provide evidence for the first time that IGF feedback on GH gene expression is mediated by activation of CaM gene expression at the pituitary level.

Calcium controls the transcription of its own transporters and channels in developing neurons

Calcium has now become important as a regulator of gene expression. Cerebellar granule cells developing in culture undergo early apoptosis unless their calcium is permitted to increase, e.g., by depolarizing their plasma membrane. The increase is kept within controlled limits by changing the pattern of transcription of calcium transporters: The IP(3) channel (but not the ryanodine channel) becomes strongly up-regulated after some days in culture in a reaction which is controlled by calcineurin. Two plasma membrane calcium pumps (isoforms PMCA2 and PMCA3) also become strongly up-regulated after some days; one (PMCA1) experiences instead a splicing switch which up-regulates a truncated variant of the isoform. By contrast, one splicing variant of the isoform PMCA4 and one of the Na/Ca exchangers of the plasma membrane (NCX2) become very rapidly down-regulated: Their down-regulation is also controlled by calcineurin. The altered pattern of Ca(2+) transporter expression is likely to reflect development-linked changes in the demands for calcium signaling in different domains of the neuronal cell.

Effects of the protein tyrosine kinase inhibitor, herbimycin A, on prolactin gene expression in GH3 and 235-1 pituitary tumor cells

The high basal level of prolactin (PRL) gene expression in rat pituitary GH3 cells is maintained through the spontaneous activity of voltage-sensitive calcium channels (VSCCs). This can be observed experimentally by addition of 0.5 mM CaCl2 to GH3 cells cultured in a low calcium, serum-free medium. CaCl2 specifically induces PRL gene expression and this induction is inhibited by VSCC blockers. PRL gene expression is also stimulated by several hormones and growth factors. In the present study, we examined the effects of tyrosine kinase inhibitors on the ability of CaCl2, basic fibroblast growth factor (bFGF), epidermal growth factor (EGF) and thryrotropin-releasing hormone (TRH) to increase PRL mRNA levels. Of several PTK inhibitors used, one PTK inhibitor, herbimycin A, specifically inhibited the CaCl2-induced increase in cytoplasmic and nuclear prolactin (PRL) mRNA without affecting cell viability, cell-cell and cell-matrix adhesion, or the expression of several other genes. The effects of herbimycin A were reversible. In cells pretreated with herbimycin A, PRL mRNA levels were reduced by 69 +/- 12% (P < 0.001; n = 4). Western blot analysis using anti-phosphotyrosine antibody revealed a decrease of 91 +/- 1% (P < 0.001; n = 4) in the phosphotyrosine content of proteins in the molecular weight range of 130-160 kDa. After changing the medium back to SFM plus 0.5 mM CaCl2, levels of PRL mRNA increased over a period of several hours, and this increase was accompanied by the tyrosine phosphorylation of two or more proteins in the approximate size range of 130-160 kDa. Herbimycin A also inhibited PRL gene expression in the independently-derived 235-1 lactotrope cell line and lowered the tyrosine specific phosphorylation of protein(s) in a similar size range. Herbimycin A inhibited the ability of bFGF, EGF and TRH to stimulate PRL gene expression in GH3 cells. Again, in cells pretreated with herbimycin A, bFGF induced a reappearance of tyrosine-specific phosphorylation, followed by a reappearance of PRL mRNA. These findings provide evidence for a role for at least one PTK which is necessary for basal and stimulated PRL gene expression.

Role of cell-cell adhesion in the regulation of prolactin gene expression by extracellular CaCl(2)

We have investigated a role for calcium-dependent cell-cell adhesion in the regulation of prolactin gene expression in rat pituitary GH(3) cells. Cells cultured in a calcium-free, serum-free medium (SFM) express low levels of prolactin and growth hormone mRNA. As expected, addition of 0.5 mM CaCl(2) to GH(3) cells in SFM produced a specific, severalfold increase in prolactin mRNA levels. CaCl(2) also promoted intercellular adhesion, during which cells assembled end-to-end in to cords. Prolactin mRNA increased after a delay of several hours. This latency period ranged from 4-12 h among different experiments, but always occurred after the onset of cell-cell adhesion. The voltage-sensitive calcium channel (VSCC) blocker, nitrendipine, inhibited the CaCl(2)-induced increase in prolactin mRNA without affecting cord formation. However, the VSCC agonist, BAY K-8644, was unable to induce prolactin gene expression prior to the onset of intercellular adhesion at 8 h, even though it produced a cellular response (tyrosine phosphorylation of a ca. 130-kDa protein) within 30 min. Blocking cell-cell adhesion inhibited the calcium-dependent induction of prolactin gene expression. Low levels (0.0025-0.02%) of trypsin blocked cell-cell adhesion and the prolactin mRNA induction by CaCl(2) without affecting the levels of other mRNAs or cell-matrix adhesion. Heparin also specifically blocked the induction of both cell-cell adhesion and prolactin gene expression. Based on these data, we propose a role for both VSCCs and calcium-dependent cell-cell adhesion in the induction of prolactin gene expression by extracellular CaCl(2).

Addition of calmodulin antagonists to NRK cells during G1 inhibits proliferating cell nuclear antigen expression

The mRNAs of most proteins involved in DNA synthesis show an S phase correlated expression when mammalian cells are stimulated to proliferate from G0. This is the case for proliferating cell nuclear antigen (PCNA), a cofactor of DNA polymerase delta that is essential for the synthesis of the leading and lagging strands of DNA. Normal rat kidney cells re-entering the cell cycle from quiescence start DNA synthesis at 12 h and reach a maximum at 20 h. The expression of PCNA parallels the synthesis of DNA. Progression through the S phase was inhibited by addition of the anticalmodulin drug W13 to the cells during G1, 5 h after activation. W13 also inhibited the increase in both PCNA protein and mRNA indicating that calmodulin regulates its expression. Using TK-ts13 cells transfected with a plasmid containing the thymidine kinase gene under the control of the human 2.8 kb PCNA promoter, we demonstrated that this promoter is not regulated by calmodulin. The half-life of PCNA mRNA during G1/S transition was not modified by the treatment with W13, indicating that the decrease in the mRNA found when calmodulin was inhibited is not due to changes in its stability. Run-on assays revealed that control cells produced predominantly complete PCNA transcripts during S phase, while short incomplete transcripts were generated in W13-treated cells at the same time. These results indicate that calmodulin participates in a more direct or indirect way during G1 in the activation of PCNA expression. From data presented here it can be suggested that calmodulin activates the release of a transcriptional block leading to an increase in the amount of PCNA during S phase.

Protein kinase C regulates calmodulin expression in NRK cells activated to proliferate from quiescence

We have investigated the levels of calmodulin protein and calmodulin mRNA species during proliferative activation of NRK cells. Cells activated to proliferate from quiescence started to replicate DNA at 15 h, reaching a maximum at 20 h after serum addition. The maximum of mitosis was observed at 24 h. Quiescent cells showed a calmodulin concentration of 1.5 ng/micrograms of protein. At 10 h after serum addition the amount of calmodulin started to increase, reaching values of 3.0 ng/micrograms of protein at 24 h. NRK cells expressed predominantly 3 species of calmodulin transcripts: the 1.7 kb from CaM I, the 1.4 kb from CaM II and the 2.3 kb from CaM III. The amount of all the 3 transcripts was low in quiescent cells and 10 h after activation the levels were already high, reaching a maximum around 20 h. At the latter time the amount of the 3 calmodulin mRNAs was 5-10-fold higher than in serum starved cells. Run-on experiments showed that at 20 h after activation the transcription rates of the 3 calmodulin genes were higher than in quiescent cells. The addition of protein kinase C inhibitors to the cultures blocked the increase of the calmodulin transcripts while inhibitors of protein kinase A did not have any effect. Moreover, the addition of submitogenic doses of phorbol 12-tetradecanoate induced the increase of all 3 calmodulin transcripts. These results indicate that protein kinase C regulates calmodulin expression when NRK cells are activated to proliferate.

Nuclear calmodulin/62 kDa calmodulin-binding protein complexes in interphasic and mitotic cells

We report here that a 62 kDa calmodulin-binding protein (p62), recently identified in the nucleus of rat hepatocytes, neurons and glial cells, consists of four polypeptides showing pI values between 5.9 and 6.1. By using a DNA-binding overlay assay we found that the two most basic of the p62 polypeptides bind both single- and double-stranded DNA. The intranuclear distribution of calmodulin and p62 was analysed in hepatocytes and astrocyte precursor cells, and in proliferating and differentiated astrocytes in primary cultures by immunogold-labeling methods. In non-dividing cells nuclear calmodulin was mostly localized in heterochromatin although it was also present in euchromatin and nucleoli. A similar pattern was observed for p62, with the difference that it was not located in nucleoli. p62/calmodulin complexes, mainly located over heterochromatin domains were also observed in interphasic cells. These complexes remained associated with the nuclear matrix after in situ sequential extraction with nucleases and high-salt containing buffers. In dividing cells, both calmodulin and p62 were found distributed over all the mitotic chromosomes but the p62/calmodulin aggregates were disrupted. These results suggest a role for calmodulin and p62 in the condensation of the chromatin.

Calcium and calcium-binding proteins in the nucleus

Calcium has long been known to play a role as a key cytoplasmic second messenger, but until relatively recently its possible involvement in nuclear signal transduction and the regulation of nuclear events has not been extensively studied. Evidence revealing the presence of transmembrane nuclear Ca2+ gradients and a variety of intranuclear Ca2+ binding proteins has fueled renewed interest in this key ion and its involvement in cell-cycle timing and division, gene expression, and protein activation. This review will offer an overview of the current state of knowledge and theory regarding calcium orchestration of nuclear functions and events and discuss possible future directions in this field of study.

Expression of calmodulin and calmodulin binding proteins in lymphoblastoid cells

Calmodulin is encoded in vertebrates by three different genes: CALM1, CALM2, and CALM3. We have examined the mRNAs expressed from these three genes in eight lines of human lymphoblastoid cells (Namalwa, Raji, Ramos, JY, Molt-4, Jurkat, CEM, and HPB-ALL). We found that all these cell lines (except Ramos) overexpressed CALM3 transcripts, which led to an increase of total CaM protein with respect to quiescent normal T lymphocytes. The nuclear concentration of calmodulin was measured in two of these lymphoblastoid cell lines (JY and HPB-ALL) and compared to quiescent and phytohemagglutinin-activated T lymphocytes. Activated lymphocytes showed a 2-fold increase of nuclear calmodulin with respect to quiescent cells, whereas in the two lymphoblastoid cell lines, nuclear calmodulin remained similar to that of quiescent cells. The levels of a calmodulin-binding protein of 150 kDa in the homogenates of the eight lymphoblastoid lines was found to be higher than those of quiescent and activated lymphocytes. Likewise, the amount of three calmodulin-binding proteins of 240, 200, and 170 kDa was also increased in several of the cell lines, but not in all of them. The 170-kDa protein was only expressed by activated lymphocytes and lymphoblastoid cells, suggesting that it could be specific for proliferating cells. In the nuclei of activated lymphocytes and lymphoblastoid cells, a decrease of a calmodulin-binding protein of 110 kDa and increases of three other of 240, 180 and 170 kDa were also detected.

Confocal microscopy to analyze cytosolic and nuclear calcium in cultured vascular cells

With the development of calcium-sensitive fluorescent dyes and videomicroscopic imaging, several investigators have located the changes in intracellular calcium in the cytoplasm, in the perinuclear region, and possibly in the nucleus. However, the presence of calcium in the nucleus is often difficult to ascertain because the fluorescence derived from the perinuclear area interferes with that of the nucleus. We have used confocal microscopy together with two calcium-sensitive dyes [acetoxymethyl esters of fluo 3 (fluo 3-AM) and rhod 2 (rhod 2-AM)] to analyze the cytosolic and nuclear calcium distribution in vascular smooth muscle and endothelial cells studied at rest and after stimulation with receptor-dependent (angiotensin, vasopressin) and receptor-independent (KCl) stimuli. With fluo 3-AM, the baseline fluorescence was located in the cytoplasm but was slightly higher in the nucleus. With all stimuli, the fluorescence intensity increased in both compartments but remained more pronounced within the nucleus. Yet, after calibration, the cytosolic calcium concentration was greater than that of the nucleus at rest and was equally high after stimulation, suggesting different properties of fluo 3 in the cytosol and in the nucleus. With rhod 2-AM, baseline fluorescence was low in the nucleus and high in the cytosol. Cell stimulation caused an initial increase in cytosolic calcium with no change in the nucleus followed by a rise in both compartments. Thus the stimulation of vascular cells is associated with marked increases in cytosolic and nuclear calcium. Fluo 3-AM seems to be a better indicator of nuclear calcium than rhod 2-AM. The increases in nuclear calcium induced by angiotensin II and vasopressin may contribute to their cell proliferative effect.

Identification and characterization of nuclear calmodulin-binding proteins of Saccharomyces cerevisiae

Nuclear calmodulin-binding proteins of the yeast Saccharomyces cerevisiae were investigated. The soluble fractions after serial treatments of the isolated nuclei with buffers containing the nonionic detergent NP-40 (F1), 0.5 M KCl (F2) and 2.0 M KCl (F3) in this order, and the residual proteins (F4) were obtained. The calmodulin-binding proteins of the nucleus and nuclear subfractions were identified using the gel overlay method using 125I-calmodulin. Each subnuclear fraction contained a large number of components that bound calmodulin in a Ca(2+)-dependent or -independent manners. The calmodulin-binding proteins were isolated from F1 and F2 subnuclear fractions by affinity chromatography. The affinity-purified proteins bound calmodulin in a Ca(2+)-dependent manner when analyzed using the gel overlay method. The major calmodulin-binding components of F1 were 44, 42, 36, 32 and 29 kDa proteins, and those of F2 were 200, 100, 40, 42, 36, 34 and 32 kDa proteins. The isolated proteins also contained several Coomassie-blue stained proteins that did not bind calmodulin and, therefore, may represent the proteins associated with the calmodulin-binding proteins. Antisera raised against the affinity-purified preparation of F1 and F2 recognized almost all of the calmodulin-binding proteins present in the fraction and several other proteins of the nucleus. The presence of Ca(2+)-dependent protein phosphatase (type 2B) in the nucleus was demonstrated by Western blotting. The enzyme was localized predominantly in F1 and F4.

Nuclear calmodulin-binding proteins in rat neurons

By using a 125I-calmodulin overlay assay, three major high-affinity calmodulin-binding proteins, showing apparent molecular masses of 135, 60, and 50 kDa, have been detected in purified nuclear fractions isolated from rat neurons. It has been shown that after extraction of the nuclei with nucleases and high salt, all these proteins remain strongly associated with the nuclear matrix. The 60- and 50-kDa proteins have been previously identified as subunits of the calmodulin-dependent protein kinase II. We report here the immunoblot identification of the 135-kDa calmodulin-binding protein as myosin light chain kinase. We also show that the calmodulin-dependent protein phosphatase calcineurin is present in the neuronal nuclei and associated with the nuclear matrix. The nuclear localization of both calcineurin and myosin light chain kinase has been confirmed by immunocytochemical studies.

Structure of the tilapia (Oreochromis mossambicus) prolactin I gene

The tilapia (Oreochromis mossambicus) prolactin-I (PRL-I) gene has been cloned and sequenced. Its transcript (3,677 bases long) begins with a guanine and is organized in five exons and four introns like the other known prolactin genes. Analysis of the 1,555-bp 5'-flanking region suggests that pituitary-specific expression of the gene could be regulated through a trans-factor related to the mammalian pituitary-specific factor Pit-1. Two potential binding sites for such a factor were found in the first intron, suggesting a possible regulatory role for this region. Moreover, two potential Z-DNA regions are located at positions -837 to -812 and -246 to -179 from the transcription start site. These two regions could play an important role in the regulation of PRL gene expression.

Confocal microscopy of fertilization-induced calcium dynamics in sea urchin eggs

Although confocal microscopy has typically been utilized in studies of fixed specimens, its potential for exploring dynamic processes in living cells is rapidly being realized. In this report, confocal laser scanning microscopy is used to analyze the calcium wave that occurs following fertilization in living sea urchin eggs microinjected with the calcium-sensitive fluorescent probes fluo-3 or calcium green. Time-lapse recordings of optical sections depicting calcium dynamics within the eggs are also subjected to volumetric reconstructions. Such analyses indicate that (1) cytoplasmic free calcium levels become elevated throughout the fertilized egg, (2) fertilization also causes the egg nucleus to undergo a transient increase in free calcium, and (3) normal cleavage can be obtained following time-lapse imaging of the calcium waves.

Presence of calmodulin and calmodulin-binding proteins in the nuclei of brain cells

The nuclear calmodulin levels have been measured in rat neurons and glial cells. The values are 1.0 and 1.1 micrograms/mg of protein, respectively. These levels are about threefold higher than those in the nuclei of rat liver cells. We have also investigated the presence of several calmodulin-binding proteins in the nuclei of both brain cellular types. As similarly observed in the nuclei of liver cells, we detected the presence of alpha-spectrin and a 62-kDa calmodulin-binding protein (p62) in the nuclei of neurons and glial cells by immunoblotting and immunocytochemical methods. Both proteins are enriched in the purified nuclear matrix samples from both cellular types. In contrast to that occurring in rat hepatocytes, we have not been able to detect, by immunoblotting methods, caldesmon in the nuclear matrices of neurons and glial cells. The immunocytochemical studies suggest, however, that caldesmon can be present in the nuclei but in a fraction distinct from the nuclear matrices.

Simultaneous monitoring of cytosolic free calcium and exocytosis at the single cell level

Abstract Quinacrine, a fluorescent basic molecule, accumulates in secretory granules of pituitary cells, as was revealed by its colocalization with immunoreactive prolactin. Thus quinacrine fluorescence may be used to monitor secretory activity at the single cell level. Rat pituitary cells in primary culture were loaded with quinacrine and stimulated with physiological secretagogues, such as thyrotrophin-releasing hormone or bradykinin, which induced a multiphasic lowering of fluorescence, corresponding to the loss of quinacrine contained in exocytosed granules. Quinacrine was further used in combination with the fluorescent calcium probe fura-2, in order to monitor simultaneously exocytosis and variations in the cytosolic free calcium concentration, [Ca(2+)](i). With an appropriate selection of the excitation wavelengths, in dual excitation microfluorimetry experiments, it was possible to distinguish between fluorescence changes due to altered [Ca(2+)](i) versus quinacrine exocytosis. Transient elevations of [Ca(2+)](i) were provoked in individual pituitary cells by enhancing calcium influx through voltage gated channels. In part of the cells an initial increase in [Ca(2+)](i) coincided with stimulated quinacrine release. The approach was also applied to cells of the neuroblastoma line NCB20, where stimulation with bradykinin caused a transient rise in [Ca(2+)](i), concomitantly with enhanced exocytosis. No increase in exocytosis was ever detected without an elevation of [Ca(2+)](i), suggesting that in both cellular systems, an increase in [Ca(2+)](i), is absolutely necessary, but not sufficient to induce secretion.

The stimulatory effect of estradiol 17-beta on prolactin mRNA is inhibited by anti-calmodulin drugs

The stimulatory action of estrogens on prolactin (PRL) secretion and synthesis is well known; on the other hand, anti-calmodulin drugs have recently been shown to inhibit prolactin in vitro release induced by estrogens. Based on these data, we decided to evaluate the in vivo effect of anti-calmodulin drugs (trifluoperazine and W7) on basal and estradiol-17 beta stimulated levels of PRL mRNA in anterior pituitary lobes obtained from adult male rats. Total RNA was isolated from pooled pituitaries recovered from animals under the same treatment and, from it, hybridizable PRL mRNA was detected. Estradiol-17 beta consistently stimulated PRL mRNA levels by 3-4 fold. The utilization of either trifluoperazine or W7, invariably inhibited estradiol-17 beta stimulated PRL mRNA. Metoclopramide, a drug with antidopaminergic activity, potentiated the stimulatory effect of estradiol-17 beta on PRL mRNA levels. These results suggest that anti-calmodulin drugs have an in vivo antiestrogenic effect on PRL mRNA levels confirming previous in vitro studies. Although, it is difficult to be conclusive about the mechanism through which these drugs act, one possibility is that the calcium-calmodulin system may be involved.

Calcium and calmodulin regulation of prolactin gene expression

Prolactin gene transcription is critically dependent upon intracellular calcium and the calcium-binding protein calmodulin. The effects of calcium and calmodulin on the prolactin gene appear to involve defined regions of the 5'-flanking sequence, and interactions between nuclear proteins and this DNA may be related to mechanisms of transcriptional control by pituitary cell-type-specific trans-acting factors.

Effects of the DNA topoisomerase II inhibitor, VM26, on transcriptional initiation in vitro

Inhibitors of DNA topoisomerase II have been shown to influence the expression of specific genes in vivo, leading investigators to suggest that the topological state of certain genes may affect their expression. In the present study, we have examined the effects of the topoisomerase II inhibitor, VM26, on transcriptional initiation in vitro. VM26 inhibited transcriptional initiation from the rat prolactin and adenovirus major late promoters in an in vitro transcription assay using rat pituitary tumor GH3 cell nuclear extracts. Transcriptional initiation from both supercoiled and linear DNA templates was equally inhibited by VM26 in a dose dependent manner. In order to identify sequences around the prolactin promoter recognized by topoisomerase II, we have mapped topoisomerase II cleavage sites using GH3 cell nuclear extracts as a source for the endogenous enzyme. Using a 910 bp genomic DNA fragment containing 423 bp of 5'-flanking sequences from the prolactin gene, we observed five VM26-enhanced topoisomerase II cleavage sites. Some of these sites map to positions near or within previously described regulatory DNA elements, and thus, may provide the structural basis for the sensitivity of prolactin gene expression to topoisomerase II inhibitors in vivo. These data suggest that inhibition of transcriptional initiation was a consequence of VM26 induced cleavage in the promoter region.

Pathophysiologic role of calcium in the development of vascular smooth muscle tone

Recent information indicates that the intracellular ionized calcium concentration [Ca2+]i plays a regulatory role not only in determining the magnitude of vascular tone but also in regulating growth of vascular tissue. Studies on living vascular smooth muscle cells using the calcium indicator aequorin have revealed that the relation between [Ca2+]i and contraction of the vascular smooth muscle cell is complex. More than 1 intracellular kinase may be involved, leading to the coexistence of multiple excitation-contraction coupling pathways. However, it appears that all of these pathways may be calcium-dependent. It is not yet known whether the cause of human essential hypertension involves an elevated [Ca2+]i in the vascular smooth muscle cell. However, evidence is presented supporting the concept that a decreased [Ca2+]i in the hypertensive smooth muscle cell will lead to a decrease in vascular tone and total peripheral resistance, and possibly also antagonize the growth response of the vascular smooth muscle cell associated with the secondary effects of hypertension.

Quantitation of calmodulin in the mammary gland of the lactating sow

It has been suggested that calmodulin, a calcium-binding protein, has a functional role during milk secretion. High levels of calmodulin are present during lactation in rat mammary glands and a substantial increase has been observed in the bovine mammary gland prior to parturition. In the sow, regressed glands involute while suckled glands remain highly active even though they are under the same hormonal influence. In this study, tissue samples were taken from suckled and regressed glands of the same sow at both peak and late lactation. Calmodulin and total protein were measured in tissue homogenate supernatants. Residual milk was apparent in regressed glands during mid lactation but not in the same glands by late lactation. Calmodulin levels in tissue were the same for both suckled and regressed glands. There was a slight but non-significant increase in the tissue calmodulin level from peak to late lactation. Protein levels declined significantly from mid to the late stage of lactation. There was no change in protein level between the suckled and regressed glands. Calmodulin may be responsible for casein phosphorylation and/or the mediation of prolactin action on the gland. The precise regulatory mechanisms relating hormonal control to calmodulin levels during lactation need further investigation.

Characterization of an intronless human calmodulin-like pseudogene

We report the isolation and characterization of a human genomic clone encoding a calmodulin-like pseudogene. It contains an open reading frame of 444 nucleotides, not interrupted by introns. The nucleotide sequence of the open reading frame shows 80%, 71% and 69% identity to the previously reported human calmodulin cDNAs lambda ht6 [17], hCWP [22], and lambda hCE1 [23], respectively. The derived amino acid sequence has only 85% identity to vertebrate calmodulin, but shows four potentially functional Ca2+-binding loops. In the human tissues tested, this pseudogene is not expressed, though gene structure including promoter elements and a putative polyadenylation site seems to be intact.

Free calcium and calmodulin levels in acinar carcinoma and normal acinar cells of rat pancreas

Exposure of acinar carcinoma cells and normal acinar cells of rat pancreas to the muscarinic agonist drug carbamylcholine stimulated 45Ca2+ outflux from 45Ca2+-labeled cells. More rapid outflux of 45Ca2+ was detected for carcinoma cells following muscarinic stimulation than for normal cells. Direct fluorometric measurement of cytosolic Ca2+ under basal (unstimulated) conditions in quin 2-loaded cells revealed significantly lower concentration of free Ca2+ in carcinoma cells (approximately 180 nM) than in normal cells (approximately 200 nM). Stimulation with 1 mM carbamylcholine increased the cytosolic Ca2+ concentration in carcinoma and normal cells to approximately 1900 nM, after which carcinoma cells removed cytosolic Ca2+ at a faster rate to a post-stimulation plateau concentration of approximately 140 nM, in comparison to normal cells which obtained a post-stimulation plateau concentration of approximately 300 nM. Essentially identical differences between carcinoma and normal cells were detected upon stimulation with the peptidergic agonist cholecystokinin octapeptide. Finally, carcinoma cells demonstrated approximately 3 times greater calmodulin concentration than normal acinar cells. Also, the calmodulin antagonist drug W7 (N-6-(aminohexyl)-5-chloro-1-naphthalene sulfonamide) inhibited the carbamylcholine-induced release of intracellular Ca2+ in acinar carcinoma cells. These results indicate that neoplastic pancreatic acinar cells have retained mechanisms of muscarinic- and peptidergic-stimulated intracellular Ca2+ release, and implicate calmodulin as a regulatory factor in secretagogue activation of intracellular Ca2+ release. We propose that the more rapid decline of intracellular Ca2+ concentration following muscarinic or peptidergic stimulation and the increased intracellular calmodulin concentration indicate calmodulin-mediated down-regulation of free cytosolic Ca2+ in acinar carcinoma cells to levels lower than those of normal cells.

Rearrangement of nuclear calmodulin during proliferative liver cell activation

Calmodulin increases about three-fold in rat liver nuclei after partial hepatectomy. The increase is maximal after 24 hours, when DNA synthesis is also maximal. During the same time re-distribution of calmodulin within the nuclear structure takes place, leading to its association with the nuclear matrix. Incubation of normal rat liver nuclei with Ca2+ induces association of calmodulin with the matrix, indicating that the re-distribution of calmodulin during the replicative period is related to the increase in nuclear Ca2+. The nuclear matrix contains several calmodulin binding proteins of which one, having Mr of 130 kDa, has been identified as myosin light chain kinase (MLCK). Three acceptor proteins, having Mr of 120, 65, and 60 kDa decrease 24 hours after partial hepatectomy, MLCK and a protein of Mr 150 kDa instead increase.

The intracellular calcium antagonist, TMB-8, inhibits prolactin gene expression in GH3 cells

We examined the effects of the drug, TMB-8, which promotes sequestration of intracellular Ca2+, on the ability of extracellular Ca2+ to stimulate prolactin gene expression in GH3 cells. TMB-8 inhibited prolactin mRNA levels in a dose-dependent manner in the concentration range of 2.5-10 microM. Prolactin mRNA levels were increased about 18-fold by the addition of 0.1 mM CaCl2, and about 25-fold by the addition of 0.4 mM CaCl2. Addition of 10 microM TMB-8 reduced these levels to about 4-fold and 7-fold, respectively. At 10 microM TMB-8 did not effect total protein synthesis or the Ca2+-induced aggregation of the cells, indicating a selective inhibition by the drug of prolactin gene expression. Both TMB-8 and the calmodulin inhibitor, calmidazolium, reversed the effects of Ca2+ on prolactin mRNA levels in cells that had been pretreated for 2 days with 0.4 mM CaCl2.

Barium distinguishes separate calcium targets for synthesis and secretion of peptides in neuroendocrine cells

The effect of barium and potassium on the secretion and biosynthesis of enkephalin in bovine chromaffin cells, and prolactin and beta-endorphin in rat anterior pituitary cells, was examined to determine whether calcium-dependent secretion and biosynthesis are mediated by the same or by different calcium targets within the neuroendocrine cell. In the presence of 1.8 mM calcium, barium and potassium stimulated the secretion of all three peptides over 30 min, and increased the levels of proenkephalin and prolactin mRNA in 24 hr. These effects were inhibited by the calcium channel blocker D600. When the extracellular calcium concentration was lowered to 0.1 mM or less, secretion elicited by potassium was blocked, whereas secretion elicited by barium was enhanced, indicating that barium wholly substitutes for extracellular calcium in mediating peptide secretion. On the other hand, stimulation of proenkephalin and prolactin mRNA by both potassium and barium was inhibited when the extracellular calcium concentration was reduced. We conclude that calcium acts at two different intracellular targets to activate secretion versus biosynthesis of both enkephalin and prolactin. This appears to be the first report in which two different calcium-dependent processes in the intact cell are distinguished by a calcium ion agonist. Calcium-dependent processes such as protein phosphorylation, protein translocation, and enzyme activation may thus be related to events in the intact cell such as peptide synthesis and secretion on the basis of selective stimulation by barium.

Regional changes in calcium underlying contraction of single smooth muscle cells

The role of calcium in regulating the contractile state of smooth muscle has been investigated by measuring calcium and contraction in single smooth muscle cells with the calcium-sensitive dye fura-2 and the digital imaging microscope. The concentration of free calcium in the cytoplasm increased after stimulation of the cells by depolarization with high potassium or by application of carbachol. Changes in calcium always preceded contraction. The increase in calcium induced by these stimuli was limited to less than 1 microM. Calcium within the nucleus was also subject to a limitation of its rise during contraction. Intranuclear calcium rose from 200 nM at rest to no more than 300 nM while cytoplasmic calcium rose to over 700 nM. These apparent ceilings for both cytoplasmic and intranuclear calcium may result either from negative feedback of calcium on cytoplasmic and nuclear calcium channel gating mechanisms, respectively, or from the presence of calcium pumps that are strongly activated at the calcium ceilings.

Ca2+/calmodulin regulation of prolactin gene expression

Despite the extensive literature on the biological actions of Ca2+ and calmodulin, very little is known about their involvement in nuclear functions, e.g., regulation of specific gene expression. To date, the only genes other than prolactin and growth hormone shown to be regulated by perturbations in cell Ca2+ are those coding for two glucose-regulated proteins. However, there is a growing body of indirect evidence for nuclear functions of Ca2+ and calmodulin, and we suspect that other examples of Ca2+-regulated genes will emerge. We have described in this chapter several different experimental approaches which we have employed to examine first whether prolactin gene expression is regulated by changes in cell Ca2+ content, and then to begin searching for the components of the mechanism by which Ca2+ exerts its effects on the prolactin gene. The tentative identification of 56-kDa nuclear matrix protein as both a calmodulin-binding protein and a substrate of a Ca2+-calmodulin-dependent protein kinase suggests that NMP 56 may be a subunit of a multifunctional Ca2+-calmodulin-protein kinase. This enzyme was recently detected in the nuclear matrix fraction of neuronal nuclei, and was shown to phosphorylate a chromatin protein similar to high mobility group protein 17 (HMG 17). Since HMG 17 is associated with actively transcribed chromatin, its phosphorylation in GH3 cells might play a role in the Ca2+-calmodulin-dependent regulation of prolactin gene expression by hormones and growth factors.

Antiestrogens are partial estrogen agonists for prolactin production in primary pituitary cultures

The antiestrogens Ly-117018 and tamoxifen increased prolactin production about 2-fold in primary cultures of male rat anterior pituitary cells. The dose-response relationship was biphasic; 10(-10) M Ly-117018 and 10(-7) M tamoxifen caused maximal stimulation, but higher concentrations caused no stimulation and completely antagonized the 5-fold stimulation caused by estrogen. The calmodulin antagonists, trifluoperazine, pimozide and W7 also prevented estrogen induction of prolactin production. Increasing concentrations of estradiol reversed inhibition by tamoxifen but not by pimozide. These results indicate that, in normal pituitary cells, estrogen antagonists may behave as partial agonists at low concentrations and as full antagonists at higher concentrations (tamoxifen, prolactin, calmodulin, 17 beta-estradiol).

Transport of beta-adrenergic antagonists in the absence of beta-adrenergic receptors in rat pituitary tumor cells

We have demonstrated that the rat pituitary tumor cell line GH3 has a carrier-mediated active transport system for the beta-adrenergic antagonist dihydroalprenolol (DHA). Transport of DHA in GH3 was saturable, with an apparent Km of 1.4 microM, was temperature and pH dependent, and was inhibited by the ionophore monensin and the amine transport inhibitor reserpine. Propranolol competed for DHA transport, but not in a stereoselective fashion. The tricyclic antidepressant imipramine also competed for DHA transport, but catecholamines or serotonin did not. This amine transport system in GH3 cells appeared to be identical to the one we recently described in several other cell types; however, analysis in those cells was complicated by the fact that they contain beta-adrenergic receptors which bind beta-adrenergic ligands. In this report we show that GH3 cells do not possess detectable beta-adrenergic receptors, based on their inability to bind the partial agonist CGP-12177, their inability to bind nanomolar concentrations of DHA in a saturable, stereospecific manner, and their failure to produce cAMP in response to stimulation by beta-adrenergic agonists. Characterization of the amine transport system in GH3 cells clearly distinguishes it from receptor-mediated phenomena and should facilitate our efforts to fully understand its mechanism and significance.

Role of ion flux in the control of c-fos expression

There has been much interest in the biochemical and biophysical processes that couple extracellular signals to alterations in gene expression. While many early events associated with the treatment of cells with growth factors have been described (for example, ion flux and protein phosphorylation), it has proved difficult to establish biochemical links to gene expression. Recently, the study of such genomic control signals has been facilitated by the demonstration that the c-fos proto-oncogene is rapidly and transiently induced by treatment of several cell types with polypeptide growth factors and other growth modulating substances. In one particular system it has been shown that nerve growth factor (NGF) causes a transient induction of c-fos in the phaeochromocytoma cell line PC12, within 15 min. Furthermore, the magnitude of this induction can be modulated with pharmacological agents such as peripheral-type benzodiazepines (BZDs). Thus, the study of c-fos expression in PC12 cells could yield valuable clues to the coupling mechanisms linking cell surface activation to genomic events. Here we demonstrate that c-fos is induced in PC12 cells either by receptor-ligand interaction or by agents or conditions that effect voltage-dependent calcium channels.

Effect of anticalmodulin drugs on the action of yeast alpha factor pheromone

Saccharomyces cerevisiae alpha factor pheromone arrest growth of cells of the a mating type (MAT a) at the G1 phase of the cell cycle. When treatment of MAT a cells with alpha factor was carried out in the presence of anticalmodulin drugs, trifluoperazine or chlorpromazine, the extent of cell growth arrest induced by alpha factor was reduced or even became undetectable. These results lend support to the hypothesis that calmodulin plays a role as mediator in the action of alpha factor on MAT a cells.

Calmodulin antagonists stimulate LDL receptor synthesis in human skin fibroblasts

The LDL receptor synthesis of human skin fibroblasts in the presence of the specific calmodulin antagonists trifluoperazine, condensation product of N-methyl-p-methoxyphenethylamine with formaldehyde (compound 48/80) and N-(6-aminohexyl)-5-chloro-1-naphthalenesulfonamide) (W-7) was studied. Labelling of cells with [35S]methionine followed by immunoprecipitation of radioactive LDL receptor protein with monospecific antibodies revealed that calmodulin antagonists caused a 3-fold increase in the radioactivity of the LDL receptor protein as compared with values found in control cells. A corresponding increase of high-affinity binding and internalization of 125I-labelled LDL was observed. The drugs did not influence the overall protein synthesis or the half-life of the LDL receptor. A concomitant suppression of cholesterol synthesis from [14C]mevalonolactone was found to be an independent effect. The calmodulin antagonist-produced stimulation of LDL receptor synthesis could not be simulated by preincubation of cells with cyclic nucleotide analogues, cholera toxin or 3-isobutyl-1-methylxanthine, known as specific effectors of adenylate cyclase and cyclic nucleotide phosphodiesterase, respectively. Modulation of calcium concentration in the incubation medium had no reproducible effect on the rate of LDL receptor synthesis. The results implicate calmodulin as an intracellular suppressor of LDL receptor synthesis in human skin fibroblasts.

Calcium gradients in single smooth muscle cells revealed by the digital imaging microscope using Fura-2

Calcium is believed to control a variety of cellular processes, often with a high degree of spatial and temporal precision. For a cell to use Ca2+ in this manner, mechanisms must exist for controlling the ion in a localized fashion. We have now gained insight into such mechanisms from studies which measured Ca2+ in single living cells with high resolution using a digital imaging microscope and the highly fluorescent Ca2+-sensitive dye, Fura-2. Levels of Ca2+ in the cytoplasm, nucleus and sarcoplasmic reticulum (SR) are clearly different. Free [Ca2+] in the nucleus and SR was greater than in the cytoplasm and these gradients were abolished by Ca2+ ionophores. When external Ca2+ was raised above normal in the absence of ionophores, free cytoplasmic Ca2+ increased but nuclear Ca2+ did not. Thus, nuclear [Ca2+] appears to be regulated independently of cytoplasmic [Ca2+] by gating mechanisms in the nuclear envelope. The observed regulation of intranuclear Ca2+ in these contractile cells may thus be seen as a way to prevent fluctuation in Ca2+-linked nuclear processes during the rise in cytoplasmic [Ca2+] which triggers contraction. The approach described here offers the opportunity of following changes in Ca2+ in cellular compartments in response to a wide range of stimuli, allowing new insights into the role of local changes in Ca2+ in the regulation of cell function.