Electroformed pure iron as a new biomaterial for degradable stents: in vitro degradation and preliminary cell viability studies

In the search for a metallic material showing moderate and uniform degradation for application as degradable cardiovascular stents, electroformed iron (E-Fe) was evaluated by in vitro degradation and cell viability tests. Static immersion and dynamic degradation were used to evaluate degradation rate and mechanism, while cell viability assay was used to assess cytotoxicity. The results were compared with those of iron fabricated by casting and thermomechanical treatment previously investigated as a stent material. Electroformed iron showed faster degradation than iron fabricated by casting (0.25 vs. 0.14 mm year(-1)), with a uniform degradation mechanism. Cell viability results showed that E-Fe did not result in a decrease in metabolic activity when exposed to primary rat smooth muscle cells. However, it caused a decrease in cell proliferation activity which could be beneficial for the inhibition of in-stent restenosis.

Cell biology of caveolae and caveolin

Originally described in the 1950s caveolae are morphologically identifiable as small omega-shaped plasma membrane invaginations present in most cell types. Caveolae are particularly abundant in adipocytes, fibroblasts, type 1 pneumocytes, endothelial and epithelial cells as well as in smooth and striated muscle cells. The first proposed function for caveolae was that of mediating the internalisation and transendothelial trafficking of solutes. Caveolae have been the object of intense research since the discovery of a biochemical marker protein, caveolin, in the early 1990s. Three genes encoding for caveolins have been characterised in mammals. Caveolins (18-24 kDa) are integral membrane proteins that constitute the major protein component of caveolar membrane in vivo. In addition to a structural role of caveolins in the formation of caveolae, caveolin protein interacts directly, and in a regulated manner, with a number of signalling molecules. We present here a general overview of the current knowledge on the structural role of caveolin in caveolae formation, and implication of caveolin in the control of cell signalling.

Reduction of caveolin 1 gene expression in lung carcinoma cell lines

Caveolae are plasma membrane microdomains that have been implicated in organizing and concentrating certain signaling molecules. Caveolins, constitute the main structural proteins of caveolae. Caveolae are abundant in terminally differentiated cell types. However, caveolin-1 is down-regulated in transformed cells and may have a potential tumor suppressor activity. In the lung, caveolae are present in the endothelium, smooth muscle cells, fibroblasts as well as in type I pneumocytes. The presence of caveolae and caveolin expression in the bronchial epithelium, although probable, has not been investigated in human. We were interested to see if the bronchial epithelia express caveolins and if this expression was modified in cancer cells. We thus tested for caveolin-1 and -2 expression several bronchial epithelial primary cell lines as well as eight lung cancer cell lines and one larynx tumor cell line. Both caveolin-1 and -2 are expressed in all normal bronchial cell lines. With the exception of Calu-1 cell line, all cancer cell lines showed very low or no expression of caveolin-1 while caveolin-2 expression was similar to the one observed in normal bronchial epithelial cells.

[Mechanisms of shedding of a soluble form of the TSH receptor]

The thyrotropin (TSH) receptor in human-thyroid glands is cleaved into an extracellular alpha subunit and a transmembrane beta subunit held together by disulfide bridges. An excess of the latter component relative to the former suggests shedding of the ectodomain. Indeed we observed such shedding in cultures of human thyrocytes and permanently transfected L or Chinese hamster ovary cells. Shedding was increased by inhibitors of endocytosis, recycling and lysosomal degradation suggesting that it was dependent on receptor residency at the cell surface. It was slightly increased by TSH and phorbol esters whereas forskolin and 8 bromo cAMP were without effect. The complete inhibition of soluble TSH receptor shedding by the specific inhibitor BB-2116 indicated that the cleavage reaction is catalyzed probably at the cell surface by a matrix metalloprotease-like enzyme. Shedding of the TSH receptor alpha domain is the consequence of two events: cleavage of the proreceptor into alpha and beta subunits and reduction of the disulfide bridge(s). The use of different specific inhibitors including monoclonal antibodies allowed us to implicate the enzyme protein disulfide isomerase in the reduction of TSHR disulfide bounds. The shed alpha subunit probably results in circulating TSH receptor ectodomain detected in human blood. This shedding mechanism might be implicated in the development of autoimmune diseases.

Inhibition of adenylyl cyclase by caveolin peptides

Caveolae and their principal component caveolin have been implicated in playing a major role in G protein-mediated transmembrane signaling. We examined whether caveolin interacts with adenylyl cyclase, an effector of G protein signaling, using a 20-mer peptide derived from the N-terminus scaffolding domain of caveolin-1. When tissue adenylyl cyclases were examined, cardiac adenylyl cyclase was inhibited more potently than other tissue adenylyl cyclases. The caveolin-1 peptide inhibited type V, as well as type III adenylyl cyclase, overexpressed in insect cells, whereas the same peptide had no effect on type II. The caveolin-3 scaffolding domain peptide similarly inhibited type V adenylyl cyclase. In contrast, peptides derived from the caveolin-2 scaffolding domain and a caveolin-1 nonscaffolding domain had no effect. Kinetic studies showed that the caveolin-1 peptide decreased the maximal rate (Vmax) value of type V without changing the Michaelis constant (Km) value for the substrate ATP. Studies with various truncations and point mutations of this peptide revealed that a minimum of 16 amino acid residues and intact aromatic residues are important for the inhibitory effect. The potency of inhibition was greater when adenylyl cyclase was in stimulated condition vs. basal condition. Thus, caveolin may be another cellular component that regulates adenylyl cyclase catalytic activity. Our results also suggest that the caveolin peptide may be used as an isoform-selective inhibitor of adenylyl cyclase.

Caveolin interaction with protein kinase C. Isoenzyme-dependent regulation of kinase activity by the caveolin scaffolding domain peptide

Caveolar localization of protein kinase C and the regulation of caveolar function by protein kinase C are well known. This study was undertaken to examine whether caveolin subtypes interact with various protein kinase C isoenzymes using the caveolin scaffolding domain peptide. When protein kinase C-alpha, -epsilon, and -zeta were overexpressed in COS cells followed by subcellular fractionation using the sucrose gradient method, all the isoenzymes (alpha, epsilon, and zeta) were detected in the same fraction as caveolin. The scaffolding domain peptide of caveolin-1 and -3, but not -2, inhibited the kinase activity and autophosphorylation of protein kinase C-alpha and -zeta, but not of protein kinase C-epsilon, overexpressed in insect cells. Truncation mutation studies of the caveolin-1 and -3 peptides demonstrated that a minimum of 16 or 14 amino acid residues of the peptide were required for the inhibition or direct binding of protein kinase C. Thus, the caveolin peptide physically interacted with protein kinase C and regulated its function. Further, this regulation occurred in a protein kinase C isoenzyme-dependent manner. Our results may provide a new mechanism regarding the regulation of protein kinase C isoenzyme activity and the molecular interaction of protein kinase C with its putative binding proteins.

Interaction of a receptor tyrosine kinase, EGF-R, with caveolins. Caveolin binding negatively regulates tyrosine and serine/threonine kinase activities

Caveolin, a 21-24-kDa integral membrane protein, is a principal component of caveolae membranes. We and others have suggested that caveolin functions as a scaffolding protein to organize and concentrate certain caveolin-interacting signaling molecules within caveolae membranes. In this regard, it has been shown that a 20-amino acid membrane-proximal region of the cytosolic NH2-terminal domain of caveolin is sufficient to mediate the interaction of caveolin with signaling proteins, namely G-proteins, Src-like kinases, eNOS, and H-Ras. This caveolin-derived protein domain has been termed the caveolin-scaffolding domain. Binding of the caveolin-scaffolding domain functionally suppresses the activity of G-protein alpha subunits, eNOS, and Src-like kinases, suggesting that caveolin binding may also play a negative regulatory role in signal transduction. Here, we report the direct interaction of caveolin with a growth factor receptor, EGF-R, a known caveolae-associated receptor tyrosine kinase. Two consensus caveolin binding motifs have been previously defined using phage display technology. One of these motifs is present within the conserved kinase domains of most known receptor tyrosine kinases (termed region IX). We now show that this caveolin binding motif within the kinase domain of the EGF-R can mediate the interaction of the EGF-R with the scaffolding domains of caveolins 1 and 3 but not with caveolin 2. In addition, the scaffolding domains of caveolins 1 and 3 both functionally inhibit the autophosphorylation of the EGF-R kinase in vitro. Importantly, this caveolin-mediated inhibition of the EGF-R kinase could be prevented by the addition of an EGF-R-derived peptide that (i) contains a well conserved caveolin binding motif and (ii) is located within the kinase domain of the EGF-R and most known receptor tyrosine kinases. Similar results were obtained with protein kinase C, a serine/threonine kinase, suggesting that caveolin may function as a general kinase inhibitor. The implications of our results are discussed within the context of caveolae-mediated signal transduction. In this regard, caveolae-coupled signaling might explain how linear signaling pathways can branch and interconnect extensively, forming a signaling module or network.

Cell-type and tissue-specific expression of caveolin-2. Caveolins 1 and 2 co-localize and form a stable hetero-oligomeric complex in vivo

Caveolae are microdomains of the plasma membrane that have been implicated in organizing and compartmentalizing signal transducing molecules. Caveolin, a 21-24-kDa integral membrane protein, is a principal structural component of caveolae membrane in vivo. Recently, we and other laboratories have identified a family of caveolin-related proteins; caveolin has been re-termed caveolin-1. Here, we examine the cell-type and tissue-specific expression of caveolin-2. For this purpose, we generated a novel mono-specific monoclonal antibody probe that recognizes only caveolin-2, but not caveolins-1 and -3. A survey of cell and tissue types demonstrates that the caveolin-2 protein is most abundantly expressed in endothelial cells, smooth muscle cells, skeletal myoblasts (L6, BC3H1, C2C12), fibroblasts, and 3T3-L1 cells differentiated to adipocytes. This pattern of caveolin-2 protein expression most closely resembles the cellular distribution of caveolin-1. In line with these observations, co-immunoprecipitation experiments with mono-specific antibodies directed against either caveolin-1 or caveolin-2 directly show that these molecules form a stable hetero-oligomeric complex. The in vivo relevance of this complex was further revealed by dual-labeling studies employing confocal laser scanning fluorescence microscopy. Our results indicate that caveolins 1 and 2 are strictly co-localized within the plasma membrane and other internal cellular membranes. Ultrastructurally, this pattern of caveolin-2 localization corresponds to caveolae membranes as seen by immunoelectron microscopy. Despite this strict co-localization, it appears that regulation of caveolin-2 expression occurs independently of the expression of either caveolin-1 or caveolin-3 as observed using two different model cell systems. Although caveolin-1 expression is down-regulated in response to oncogenic transformation of NIH 3T3 cells, caveolin-2 protein levels remain unchanged. Also, caveolin-2 protein levels remain unchanged during the differentiation of C2C12 cells from myoblasts to myotubes, while caveolin-3 levels are dramatically induced by this process. These results suggest that expression levels of caveolins 1, 2, and 3 can be independently up-regulated or down-regulated in response to a variety of distinct cellular cues.

Dissecting the interaction between nitric oxide synthase (NOS) and caveolin. Functional significance of the nos caveolin binding domain in vivo

Endothelial nitric oxide synthase (eNOS) is a dually acylated peripheral membrane protein that targets to the Golgi region and caveolae of endothelial cells. Recent evidence has shown that eNOS can co-precipitate with caveolin-1, the resident coat protein of caveolae, suggesting a direct interaction between these two proteins. To test this idea, we examined the interactions of eNOS with caveolin-1 in vitro and in vivo. Incubation of endothelial cell lysates or purified eNOS with glutathione S-transferase (GST)-caveolin-1 resulted in the direct interaction of the two proteins. Utilizing a series of GST-caveolin-1 deletion mutants, we identified two cytoplasmic domains of caveolin-1 that interact with eNOS, the scaffolding domain (amino acids 61-101) and to a lesser extent the C-terminal tail (amino acids 135-178). Incubation of pure eNOS with peptides derived from the scaffolding domains of caveolin-1 and -3, but not the analogous regions from caveolin-2, resulted in inhibition of eNOS, inducible NOS (iNOS), and neuronal NOS (nNOS) activities. These results suggest a common mechanism and site of inhibition. Utilizing GST-eNOS fusions, the site of caveolin binding was localized between amino acids 310 and 570. Site-directed mutagenesis of the predicted caveolin binding motif within eNOS blocked the ability of caveolin-1 to suppress NO release in co-transfection experiments. Thus, our data demonstrate a novel functional role for caveolin-1 in mammalian cells as a potential molecular chaperone that directly inactivates NOS. This suggests that the direct binding of eNOS to caveolin-1, per se, and the functional consequences of eNOS targeting to caveolae are likely temporally and spatially distinct events that regulate NO production in endothelial cells. Additionally, the inactivation of eNOS and nNOS by the scaffolding domain of caveolin-3 suggests that eNOS in cardiac myocytes and nNOS in skeletal muscle are likely subject to negative regulation by this muscle-specific caveolin isoform.

Identification of peptide and protein ligands for the caveolin-scaffolding domain. Implications for the interaction of caveolin with caveolae-associated proteins

Caveolin, a 21-24-kDa integral membrane protein, is a principal component of caveolae membranes. We have suggested that caveolin functions as a scaffolding protein to organize and concentrate certain caveolin-interacting proteins within caveolae membranes. In this regard, caveolin co-purifies with a variety of lipid-modified signaling molecules, including G-proteins, Src-like kinases, Ha-Ras, and eNOS. Using several independent approaches, it has been shown that a 20-amino acid membrane proximal region of the cytosolic amino-terminal domain of caveolin is sufficient to mediate these interactions. For example, this domain interacts with G-protein alpha subunits and Src-like kinases and can functionally suppress their activity. This caveolinderived protein domain has been termed the caveolin-scaffolding domain. However, it remains unknown how the caveolin-scaffolding domain recognizes these molecules. Here, we have used the caveolin-scaffolding domain as a receptor to select random peptide ligands from phage display libraries. These caveolin-selected peptide ligands are rich in aromatic amino acids and have a characteristic spacing in many cases. A known caveolin-interacting protein, Gi2alpha, was used as a ligand to further investigate the nature of this interaction. Gi2alpha and other G-protein alpha subunits contain a single region that generally resembles the sequences derived from phage display. We show that this short peptide sequence derived from Gi2alpha interacts directly with the caveolin-scaffolding domain and competitively inhibits the interaction of the caveolin-scaffolding domain with the appropriate region of Gi2alpha. This interaction is strictly dependent on the presence of aromatic residues within the peptide ligand, as replacement of these residues with alanine or glycine prevents their interaction with the caveolin-scaffolding domain. In addition, we have used this interaction to define which residues within the caveolin-scaffolding domain are critical for recognizing these peptide and protein ligands. Also, we find that the scaffolding domains of caveolins 1 and 3 both recognize the same peptide ligands, whereas the corresponding domain within caveolin-2 fails to recognize these ligands under the same conditions. These results serve to further demonstrate the specificity of this interaction. The implications of our current findings are discussed regarding other caveolin- and caveolae-associated proteins.

Src tyrosine kinases, Galpha subunits, and H-Ras share a common membrane-anchored scaffolding protein, caveolin. Caveolin binding negatively regulates the auto-activation of Src tyrosine kinases

Caveolae are plasma membrane specializations present in most cell types. Caveolin, a 22-kDa integral membrane protein, is a principal structural and regulatory component of caveolae membranes. Previous studies have demonstrated that caveolin co-purifies with lipid modified signaling molecules, including Galpha subunits, H-Ras, c-Src, and other related Src family tyrosine kinases. In addition, it has been shown that caveolin interacts directly with Galpha subunits and H-Ras, preferentially recognizing the inactive conformation of these molecules. However, it is not known whether caveolin interacts directly or indirectly with Src family tyrosine kinases. Here, we examine the structural and functional interaction of caveolin with Src family tyrosine kinases. Caveolin was recombinantly expressed as a glutathione S-transferase fusion. Using an established in vitro binding assay, we find that caveolin interacts with wild-type Src (c-Src) but does not form a stable complex with mutationally activated Src (v-Src). Thus, it appears that caveolin prefers the inactive conformation of Src. Deletion mutagenesis indicates that the Src-interacting domain of caveolin is located within residues 82-101, a cytosolic membrane-proximal region of caveolin. A caveolin peptide derived from this region (residues 82-101) functionally suppressed the auto-activation of purified recombinant c-Src tyrosine kinase and Fyn, a related Src family tyrosine kinase. We further analyzed the effect of caveolin on c-Src activity in vivo by transiently co-expressing full-length caveolin and c-Src tyrosine kinase in 293T cells. Co-expression with caveolin dramatically suppressed the tyrosine kinase activity of c-Src as measured via an immune complex kinase assay. Thus, it appears that caveolin structurally and functionally interacts with wild-type c-Src via caveolin residues 82-101. Besides interacting with Src family kinases, this cytosolic caveolin domain (residues 82-101) has the following unique features. First, it is required to form multivalent homo-oligomers of caveolin. Second, it interacts with G-protein alpha-subunits and down-regulates their GTPase activity. Third, it binds to wild-type H-Ras. Fourth, it is membrane-proximal, suggesting that it may be involved in other potential protein-protein interactions. Thus, we have termed this 20-amino acid stretch of caveolin residues the caveolin scaffolding domain.

A neomutation of the thyroid-stimulating hormone receptor in a severe neonatal hyperthyroidism

Until recently, neonatal hyperthyroidism has been considered to be related to the transplacental passage of thyroid-stimulating Ig present in the serum of the mother. We report here the case of a newborn who presented with severe hyperthyroidism, diffuse goiter, and important ocular signs (eyelid retraction and possibly proptosis). However, the absence of thyroid pathology in the parents and the lack of antithyroid antibodies in the mother and in the patient led us to suspect a nonimmune aetiology. Direct genomic sequencing of the last exon of the TSH receptor in the patient revealed a T-->C transversion yielding to a Met453-->Thr heterozygous substitution in the second transmembrane domain of the receptor. The mutation was absent in both parents. Eukaryotic expression analysis in COS-7 cells yielded a mutated receptor that produced constitutive activation of adenylate cyclase without enhancement of phospholipase C activity.

Shedding of human thyrotropin receptor ectodomain. Involvement of a matrix metalloprotease

The thyrotropin (TSH) receptor in human thyroid glands has been shown to be cleaved into an extracellular alpha subunit and a transmembrane beta subunit held together by disulfide bridges. An excess of the latter component relative to the former suggested the shedding of the ectodomain. Indeed we observed such a shedding in cultures of human thyrocytes and permanently transfected L or Chinese hamster ovary cells. The shedding was increased by inhibitors of endocytosis, recycling, and lysosomal degradation, suggesting that it was dependent on receptor residency at the cell surface. It was slightly increased by TSH and phorbol esters, whereas forskolin and 8-bromo-cyclic AMP were without effect. Decreasing the serum concentration in cell culture medium enhanced the shedding by an unknown mechanism. The shedding of the TSH receptor alpha domain is the consequence of two events: cleavage of the receptor into alpha and beta subunits and reduction of the disulfide bridge(s). The complete inhibition of soluble TSH receptor shedding by the specific inhibitor BB-2116 indicated that the cleavage reaction is catalyzed probably at the cell surface by a matrix metalloprotease. This shedding mechanism may be responsible for the presence of soluble TSH receptor alpha subunit in human circulation.

Opposite effects of prolactin and corticosterone on the expression and activity of 3 beta-hydroxysteroid dehydrogenase/delta 5-delta 4 isomerase in rat skin

In rat skin, type IV is the major 3 beta-hydroxysteroid dehydrogenase/delta 5-delta 4 isomerase (3 beta-HSD) isoenzyme expressed. Although types I and II 3 beta-HSD mRNAs are also present in the skin, their level of expression is about two orders of magnitude lower than that of type IV. In this study, we have investigated the control of type IV 3 beta-HSD mRNA levels as well as 3 beta-HSD enzymatic activity in hypophysectomized adult rats of both sexes. Skin 3 beta-HSD activity was measured by the conversion of [14C]-dehydroepiandrosterone into [14C]-androstenedione, whereas ribonuclease protection assay using a specific type IV cRNA probe was used to assess mRNA levels. Intact male and female rats show a similar level of skin 3 beta-HSD activity, although hypophysectomy caused opposite effects, a decrease being observed in males while an increase was observed in hypophysectomized female animals. We next studied the effects of hyperprolactinemia, corticosterone and 1-thyroxine in hypophysectomized animals. L-thyroxine was found to stimulate 3 beta-HSD expression and activity in male rats whereas no significant effect was observed on the already elevated levels in hypophysectomized female rats. Corticosterone caused an inhibition of type IV 3 beta-HSD mRNA levels and activity in both male and female animals. Hyperprolactinemia achieved by pituitary implants inserted under the kidney capsule stimulated the expression of type IV mRNA as well as 3 beta-HSD enzymatic activity in hypophysectomized male and female animals. The present data demonstrate the multihormonal regulation of 3 beta-HSD/isomerase expression and activity in the rat skin.

Rapid modulation of ovarian 3 beta-hydroxysteroid dehydrogenase/delta 5-delta 4 isomerase gene expression by prolactin and human chorionic gonadotropin in the hypophysectomized rat

In order to better understand the role of prolactin (PRL) and luteinizing hormone (LH) on progesterone biosynthesis in the ovary, we have investigated the time course (1-9 days) of the effect of PRL and human chorionic gonadotropin (hCG) on ovarian 3 beta-hydroxysteroid dehydrogenase/delta 5-delta 4 isomerase (3 beta-HSD) expression in the hypophysectomized rat. As evaluated by quantitative in situ hybridization using a 35S labelled type I 3 beta-HSD cDNA probe, the administration of hCG for 2, 3 and 9 days induced increases of 63%, 145% and 146% above control, respectively, in 3 beta-HSD mRNA levels in ovarian interstitial cells. The absence of apparent effect of the gonadotropin in other ovarian cell types could explain the small modulation of ovarian 3 beta-HSD protein content and enzymatic activity observed in total ovarian tissue. On the other hand, treatment with PRL caused a rapid decrease in 3 beta-HSD mRNA levels in corpus luteum by 23%, 63%, 76% and 78% (P < 0.01) following 1, 2, 5 and 9 days of treatment, respectively. The short-term inhibitory effect of PRL was also observed on ovarian immunoreactive 3 beta-HSD protein, as measured by Western blot analysis, and on 3 beta-HSD activity measured by the conversion of [14C]dehydroepiandrosterone into [14C]androstenedione.(ABSTRACT TRUNCATED AT 250 WORDS)

Structure and tissue-specific expression of a novel member of the rat 3 beta-hydroxysteroid dehydrogenase/delta 5-delta 4 isomerase (3 beta-HSD) family. The exclusive 3 beta-HSD gene expression in the skin

Structures of cDNA clones encoding three members of the rat 3 beta-hydroxysteroid dehydrogenase/delta 5-delta 4 isomerase (3 beta-HSD) family were characterized. To search for potential new types of 3 beta-HSD, rat types I and II 3 beta-HSD cDNAs were used as probes to screen a rat genomic DNA library. Among the clones isolated, one encodes a novel predicted rat 3 beta-HSD isoenzyme, chronologically designated type IV. The corresponding full-length cDNA was thereafter isolated by selective polymerase chain reaction amplification from rat ovary and day-15 placenta cDNA libraries. The rat type IV 3 beta-HSD cDNA encodes a predicted 372-amino acid protein of 41,854 daltons, which shares 90.9, 87.9, and 78.8% sequence identity with rat types I, II, and III proteins, respectively. Ribonuclease protection assay reveals that type IV 3 beta-HSD is the sole 3 beta-HSD mRNA species detectable in the skin and represents the predominant species in the placenta while being also detectable in the ovary and, to a lower degree, in the adrenal gland. Transient expression of type IV cDNA in SW-13 cells indicates 3 beta-HSD activity similar to that of rat type I 3 beta-HSD. The presence of multiple 3 beta-HSD genes should permit differential and tissue-specific regulation of this rate-limiting enzymatic activity essential in the biosynthesis of all classes of steroid hormones in both classical steroidogenic and intracrine peripheral tissues.

Blockade of androstenedione-induced stimulation of androgen-sensitive parameters in the rat prostate by combination of Flutamide and 4-MA

In order to mimic the human situation in which adrenal steroid precursors are converted to the active androgen dihydrotestosterone (DHT) in prostatic tissue, we have used castrated rats supplemented with the precursor steroid androstenedione (delta 4-dione) released from Silastic implants. While it is well known that the action of DHT can be partially neutralized by antiandrogens which compete for binding to the androgen receptor, we have used 17 beta-N,N-diethylcarbamoyl-4-methyl-4-aza-5 alpha-androstan-3-one (4-MA), an inhibitor of 5 alpha-reductase, the enzyme which converts testosterone into DHT, in order to decrease intraprostatic DHT levels and thus facilitate the action of the antiandrogen. Animals were treated for 7 days with Flutamide (FLU, 2 mg) or 4-MA (4 mg) injected subcutaneously, twice daily, alone or in combination. 4-MA administered alone caused a 54% inhibition of delta 4-dione-stimulated ventral prostate weight while FLU exerted a 74% inhibitory effect and 4-MA+FLU further improved inhibition to 81%. We then measured, by in situ hybridization, the levels of prostatic mRNAs encoding the C1 and C3 components of the prostatic binding protein (PBP) which are highly specific and sensitive markers of androgen action. PBP-C3 mRNA levels fell by 95% following castration while treatment with delta 4-dione completely reversed the effect of castration. Administration of FLU or 4-MA independently caused 33% and 10% decreases, respectively, of PBP-C3 mRNA levels stimulated by delta 4-dione while the combination of both compounds further inhibited PBP-C3 mRNA levels to reach a 55% inhibition. Similar effects were observed on PBP-C1 mRNA levels.(ABSTRACT TRUNCATED AT 250 WORDS)

Regulation of 3-ketosteroid reductase messenger ribonucleic acid levels and 3 beta-hydroxysteroid dehydrogenase/delta 5-delta 4-isomerase activity in rat liver by sex steroids and pituitary hormones

We have recently characterized three types of complementary DNA clones encoding predicted isoenzymes of the rat 3 beta-hydroxysteroid dehydrogenase/delta 5-delta 4 isomerase (3 beta-HSD) family. Transient expression in nonsteroidogenic cells reveals that the type III isoenzyme specific for male liver does not display oxidative activity for classical substrates of 3 beta-HSD, in contrast to the two other 3 beta-HSD isoenzymes, thus showing exclusively 3-ketosteroid reductase (3-KSR) activity. In order to better understand the sex-specific control of 3 beta-HSD activity and type III 3-KSR gene expression in rat liver, we have studied in adult animals of both sexes the effect of sex steroids and hypophysectomy, pituitary implants, PRL, and GH on type III 3-KSR messenger RNA (mRNA) levels and 3 beta-HSD/delta 5-delta 4 isomerase activity as measured by the conversion of [14C]dehydroepiandrosterone into [14C] delta 4-androstenedione. Ribonuclease protection assay using types I-, II-, and III-specific complementary RNA probes reveals that type III transcripts are the only species detectable in liver RNA extracted from intact males, whereas no hybridization signal was detectable with any of the three probes in intact female liver RNA. In males, 15 days after castration, liver type III 3-KSR mRNA levels decreased by 80% compared to intact controls, whereas 3 beta-HSD activity was reduced by 48%. Administration of dihydrotestosterone (DHT) increased by 8.25-fold type III 3-KSR mRNA concentration and completely reversed the inhibitory effect of orchiectomy on 3 beta-HSD activity. In ovariectomized animals, treatment with DHT markedly increased type III 3-KSR mRNA accumulation and 3 beta-HSD activity, thus leading to values similar to those measured in intact males. Simultaneous treatment with 17 beta-estradiol almost completely abolished the stimulatory effect of DHT in female rats, whereas no significant effect was seen in males. Twenty-four days after hypophysectomy, type III 3-KSR mRNA levels were decreased by 50-55% in males, whereas in females these transcripts markedly increased from undetectable to 28-36% of the value measured in intact male rats. Treatment with DHT or 17 beta-estradiol for a period of 9 days starting 15 days after hypophysectomy had no effect in male and female rats. On the other hand, treatment with ovine PRL (1 mg, twice daily) had no effect in males but completely blocked the elevation of type III 3-KSR mRNA levels and 3 beta-HSD activity observed after hypophysectomy in females.(ABSTRACT TRUNCATED AT 400 WORDS)

Regulation of 3 beta-hydroxysteroid dehydrogenase/delta 5-delta 4 isomerase expression and activity in the hypophysectomized rat ovary: interactions between the stimulatory effect of human chorionic gonadotropin and the luteolytic effect of prolactin

The enzyme 3 beta-hydroxysteroid dehydrogenase/delta 5-delta 4 isomerase (3 beta-HSD) catalyzes an obligatory step in the conversion of pregnenolone and other 5-ene-3 beta-hydroxysteroids into progesterone as well as precursors of all androgens and estrogens in the ovary. Since 3 beta-HSD is likely to be an important target for regulation by pituitary hormones, we have studied the effect of chronic treatment with LH (hCG), FSH, and PRL on ovarian 3 beta-HSD expression and activity in hypophysectomized adult female rats. Human CG (hCG) [10 IU, twice a day (bid)], ovine FSH (0.5 microgram, bid), and ovine PRL (1 mg, bid) were administered, singly or in combination, for a period of 10 days starting 15 days after hypophysectomy. In hypophysectomized rats, PRL exerted a potent inhibitory effect on all the parameters studied. In fact, PRL caused a 81% decrease in ovarian 3 beta-HSD mRNA content accompanied by a similar decrease in 3 beta-HSD activity and protein levels. In addition, ovarian weight decreased by 40% whereas serum progesterone fell dramatically from 1.92 nmol/liter to undetectable levels after treatment with PRL. Whereas hCG alone had only slight stimulatory effects on 3 beta-HSD mRNA, protein content and activity levels, treatment with the gonadotropin partially or completely reversed the potent inhibitory effects of oPRL on all the parameters measured. FSH, on the other hand, had no significant effect on 3 beta-HSD expression and activity. In situ hybridization experiments using the 35S-labeled rat ovary 3 beta-HSD cDNA probe show that the inhibitory effect of PRL is exerted primarily on luteal cell 3 beta-HSD expression and activity. On the other hand, it can be seen that hCG stimulates 3 beta-HSD mRNA accumulation in interstitial cells. The present data show that hCG and PRL exert potent and opposite cell-specific effects on ovarian 3 beta-HSD expression, activity, and content in the rat ovary. Moreover, the present study could suggest that female infertility associated with hyperprolactinemia in women could well be related, at least in part, to the potent inhibitory effect of PRL on ovarian 3 beta-HSD expression and activity.

Regulation of pro-gonadotropin-releasing hormone gene expression by sex steroids in the brain of male and female rats

The fine modulation of gonadotropin gene expression and secretion is well recognized to be regulated by sex steroids through their direct action both at the anterior pituitary level and on the pulsatile pattern of GnRH secretion at the hypothalamic level. Since the influence of sex steroids on hypothalamic GnRH mRNA levels remains to be elucidated, quantitative in situ hybridization was used to study the effect of sex steroids on cellular levels of pro-GnRH mRNA in adult rats of both sexes. The effects of 14-day gonadectomy as well as administration of 17 beta-estradiol (E2, 0.25 micrograms) or dihydrotestosterone (DHT, 100 micrograms) twice a day during 14 days to gonadectomized animals were evaluated. In addition, the effect of progesterone (P, 2 mg, twice daily) alone or in the presence of E2 was also studied in ovariectomized animals. Hybridization was performed using a 35S-labeled cDNA probe encoding rat pro-GnRH and the corresponding mRNA levels were assessed by counting the number of silver grains overlying labeled neurons. In male rats, castration induced a highly significant 65% increase (compared to intact rats) in the mean number of grains per neuron. Administration of E2 or DHT to castrated animals completely prevented the post castration rise in pro-GnRH mRNA levels. In female animals, the effect of ovariectomy was less striking than in the male, a 25% increase (P less than 0.001) being observed. Treatment with E2 or DHT also completely prevented the increase in pro-GnRH mRNA levels induced by ovariectomy. Moreover, treatment with P in ovariectomized animals markedly potentiated the inhibitory effect of E2 on pro-GnRH mRNA levels.(ABSTRACT TRUNCATED AT 250 WORDS)

Characterization of two mRNA species encoding human estradiol 17 beta-dehydrogenase and assignment of the gene to chromosome 17

Using two 33-mer synthetic oligonucleotides derived from the amino acid sequence of the catalytic site of estradiol 17 beta-dehydrogenase (E2DH) and polyclonal antibodies raised against the enzyme purified from human placenta, clones were isolated from a lambda gt11 human placental cDNA library. A 327-amino acid sequence was deduced from cDNA sequencing. Two mRNA species have been identified in poly(A)+ RNA from human placenta, a major species migrating at 1.3 kb while a minor one is found at approx. 2.2 kb. Primer extension and S1 nuclease analysis indicate that the major mRNA species starts 9-10 nucleotides while the minor mRNA starts 971 nucleotides upstream from the ATG initiating codon, respectively. Sequence analysis of the longest cDNA clone (2092 bp) shows that it possesses identical coding and non-coding sequences in the regions of overlap with the shorter cDNA clones. The 32P-labeled 5' non-coding fragment hybridizes only to the 2.2 kb band, thus providing evidence for the existence of two distinct mRNA species which differ in their 5' noncoding regions. Using hp E2DH-36 cDNA as a probe for in situ hybridization of translocated chromosomes, the human E2DH gene was localized to the q11-q12 region of chromosome 17.