Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Proprotein Convertases”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 667 records · Page 37Linked to original sources
PubMed2002

Proinsulin processing in the diabetic Goto-Kakizaki rat.

The biosynthesis and processing of proinsulin was investigated in the diabetic Goto-Kakizaki (GK) rat. Immunofluorescence microscopy comparing GK and Wistar control rat pancreata revealed marked changes in the distribution of alpha-cells and pronounced beta-cell heterogeneity in the expression patterns of insulin, prohormone convertases PC1, PC2, carboxypeptidase E (CPE) and the PC-binding proteins 7B2 and ProSAAS. Western blot analyses of isolated islets revealed little difference in PC1 and CPE expression but PC2 immunoreactivity was markedly lower in the GK islets. The processing of the PC2-dependent substrate chromogranin A was reduced as evidenced by the appearance of intermediates. No differences were seen in the biosynthesis and post-translational modification of PC1, PC2 or CPE following incubation of islets in 16.7 mM glucose, but incubation in 3.3 mM glucose resulted in decreased PC2 biosynthesis in the GK islets. The rates of biosynthesis, processing and secretion of newly synthesized (pro)insulin were comparable. Circulating insulin immunoreactivity in both Wistar and GK rats was predominantly insulin 1 and 2 in the expected ratios with no (pro)insulin evident. Thus, the marked changes in islet morphology and PC2 expression did not impact the rate or extent of proinsulin processing either in vitro or in vivo in this experimental model.

Animals↗
PubMed1996

Identification of the thyrotropin-releasing hormone precursor, its processing products, and its coexpression with convertase 1 in primary cultures of hypothalamic neurons: anatomic distribution of PC1 and PC2.

The processing of pro-TRH, has been extensively studied in our laboratory using a corticotropic cell line, AtT20, transfected with the pro-TRH gene. We have also demonstrated that the convertases PC1 and PC2 process pro-TRH to cryptic peptides in vitro. However, although these processing pathways have been well characterized in vitro, little is known about the processing and subcellular distribution of pro-TRH and its derived peptides in hypothalamic neurons, an endogenous source of pro-TRH and PC enzymes. In this study we used multiple approaches to identify, both biochemically and anatomically, the presence and localization of pro-TRH (26 kDa) and its processing products. We also investigated the presence of PC1 and PC2 enzymes and the coexpression of pro-TRH and PC1 messenger RNAs. Identification of the TRH precursor was demonstrated by 1) Western blot analysis of cellular extracts, 2) immunoprecipitation of radiolabeled pro-TRH followed by analysis on acrylamide gel electrophoresis, 3) fluorescence immunocytochemistry, and 4) immunoelectron microscopy. The presence of the convertases PC1 and PC2 was determined by Western blot analysis of cellular extracts and fluorescence immunocytochemistry. The coexpression of pro-TRH with PC1 was shown by double in situ hybridization. Our findings support three main conclusions. First, this primary culture system of hypothalamic neurons is suitable for characterizing pro-TRH processing as well as identifying the anatomical location of its processing products. Second, prohormome processing takes place during axonal transport after removal of the signal peptide in the endoplasmic reticulum, and subsequent cleavages of the prohormone occur as intermediate peptides move down the axon toward the nerve terminal. This coupled transport-processing phenomenon may provide the necessary mechanism to ensure flexibility in differential processing of specific protein sequences that are determined by the secretory needs of cells. It appears that certain intermediate peptides differ in their subcompartmental distribution, suggesting the possibility of a differential processing and maturation of pro-TRH-derived peptides. Thirdly, the 87-kDa form of PC 1 may initiate the processing of pro-TRH at the Golgi complex level, which then continues to be processed by PC1 and PC2 in later stages of the secretory pathway.

Animals↗
PubMed2002

Severe block in processing of proinsulin to insulin accompanied by elevation of des-64,65 proinsulin intermediates in islets of mice lacking prohormone convertase 1/3.

The neuroendocrine processing endoproteases PC2 and PC1/3 are expressed in the beta cells of the islets of Langerhans and participate in the processing of proinsulin to insulin and C-peptide. We have previously shown that disruption of PC2 (SPC2) expression significantly impairs proinsulin processing. Here we report that disruption of the expression of PC1/3 (SPC3) produces a much more severe block in proinsulin conversion. In nulls, pancreatic and circulating proinsulin-like components comprise 87% and 91%, respectively, of total insulin-related immunoreactivity. Heterozygotes also show a more than 2-fold elevation in proinsulin levels to approximately 12%. Immunocytochemical and ultrastructural studies of the beta cells reveal the nearly complete absence of mature insulin immunoreactivity and its replacement by that of proinsulin in abundant immature-appearing secretory granules. In contrast, alpha cell morphology and glucagon processing are normal, and there is also no defect in somatostatin-14 generation. Pulse-chase labeling studies confirm the existence of a major block in proinsulin processing in PC1/3 nulls with prolongation of half-times of conversion by 7- and 10-fold for proinsulins I and II, respectively. Lack of PC1/3 also results in increased levels of des-64,65 proinsulin intermediates generated by PC2, in contrast to PC2 nulls, in which des- 31,32 proinsulin intermediates predominate. These results confirm that PC1/3 plays a major role in processing proinsulin, but that its coordinated action with PC2 is necessary for the most efficient and complete processing of this prohormone.

Animals↗
PubMed2001

Comparative tissue distribution of the processing enzymes "prohormone thiol protease," and prohormone convertases 1 and 2, in human PTHrP-producing cell lines and mammalian neuroendocrine tissues.

Peptide hormones are generated by proteolytic processing of their respective protein precursors by several prohormone processing proteases. The peptide hormone PTHrP is widely expressed in normal and malignant tissues, where proPTHrP undergoes proteolytic processing to generate PTHrP peptides with distinct biological actions. In this study, the tissue distribution of the prohormone processing enzymes PTP, PC1, and PC2 were compared by immunohistochemistry in human PTHrP-producing cancer cell lines, and in mammalian neuroendocrine and other tissues from rat and bovine that contain peptide hormones. PTP, PC1, and PC2 were prominently expressed in PTHrP-expressing human cancer cell lines originating from tumors of the breast, lung, prostate, as well as lymphoma. These processing enzymes also showed significant expression in normal mammalian neuroendocrine tissues from bovine and rat, including pituitary, hypothalamus, adrenal medulla, pancreas, and other tissues. Most neuroendocrine tissues contained prominent levels of at least two of the three processing enzymes examined, and all tissues contained at least one of these three enzymes. Differential expression of processing enzyme proteins was also demonstrated by Western blots. The differential expression of PTP, PC1, and PC2 observed in certain cancer and normal neuroendocrine cell types postulates selective roles for these processing enzymes in different tissues for generating biologically active peptide hormones. These results support the importance of these processing enzymes in their hypothesized roles in prohormone processing.

Adrenal Medulla↗
PubMed1999

The cell biology of the prohormone convertases PC1 and PC2.

Mature peptide hormones and neuropeptides are typically synthesized from much larger precursors and require several posttranslational processing steps--including proteolytic cleavage--for the formation of the bioactive species. The subtilisin-related proteolytic enzymes that accomplish neuroendocrine-specific cleavages are known as prohormone convertases 1 and 2 (PC1 and PC2). The cell biology of these proteases within the regulated secretory pathway of neuroendocrine cells is complex, and they are themselves initially synthesized as inactive precursor molecules. ProPC1 propeptide cleavage occurs rapidly in the endoplasmic reticulum, yet its major site of action on prohormones takes place later in the secretory pathway. PC1 undergoes an interesting carboxyl terminal processing event whose function appears to be to activate the enzyme. ProPC2, on the other hand, exhibits comparatively long initial folding times and exits the endoplasmic reticulum without propeptide cleavage, in association with the neuroendocrine-specific protein 7B2. Once the proPC2/7B2 complex arrives at the trans-Golgi network, 7B2 is internally cleaved into two domains, the 21-kDa fragment and a carboxy-terminal 31 residue peptide. PC2 propeptide removal occurs in the maturing secretory granule, most likely through autocatalysis, and 7B2 association does not appear to be directly required for this cleavage event. However, if proPC2 has not encountered 7B2 intracellularly, it cannot generate a catalytically active mature species. The molecular mechanism behind the intriguing intracellular association of 7B2 and proPC2 is still unknown, but may involve conformational rearrangement or stabilization of a proPC2 conformer mediated by a 36-residue internal segment of 21-kDa 7B2.

Animals↗
PubMed1996

Dissociation of the complex between the neuroendocrine chaperone 7B2 and prohormone convertase PC2 is not associated with proPC2 maturation.

7B2 is a highly conserved neuroendocrine protein that is associated with the proform of the prohormone convertase PC2 in the early stages of the secretory pathway in intermediate pituitary cells of Xenopus laevis. Subsequent processing of 7B2 and dissociation of the 7B2/proPC2 complex is thought to be associated with the conversion of proPC2 to the mature enzyme. Here, we report that, in both Xenopus and mouse intermediate cells, proPC2 maturation does not take place when the proenzyme is associated with the 7B2 precursor and that, in contrast to the previous notion, dissociation of the complex between proPC2 and the N-terminal 7B2 fragment precedes, and is thus not directly linked to, proPC2 maturation. In vitro, conversion of newly synthesized proPC2 was efficiently blocked by recombinant 7B2 and studies with truncation mutants indicated that a short segment in the C-terminal region of 7B2 is necessary and sufficient for this inhibitory effect. Our results indicate that, after 7B2 precursor processing and dissociation of the N-terminal fragment, the C-terminal fragment of 7B2 may remain associated with proPC2, thereby preventing autocatalytic conversion of the proenzyme until the appropriate site for activation in the secretory pathway is reached.

Animals↗
PubMed2003

The Arg617-Arg618 cleavage site in the C-terminal domain of PC1 plays a major role in the processing and targeting of the enzyme within the regulated secretory pathway.

The C-terminal domain of the prohormone convertase PC1 is involved in targeting of the enzyme to secretory granules in neuroendocrine cells and is subsequently processed in this compartment at an Arg617-Arg618 site. Three other dibasics are found in the C-terminal domain of mouse PC1. Here, we examined the role of the four dibasics in targeting PC1 to secretory granules. All 15 possible combinations of dibasic mutations were performed. Wild-type (WT) and mutant PC1 were stably expressed in neuroendocrine PC12 cells that lacked endogenous PC1. Processing, secretion and intracellular localization of PC1 and its mutants were analyzed. Leaving intact Arg617-Arg618 and mutating any combination of the three other dibasics yielded proteins that were stored and processed in secretory granules, similarly to WT PC1. Mutating Arg617-Arg618 alone or with any one of the three remaining dibasics generated proteins that were efficiently stored in secretory granules but were not processed further. Mutating Arg617-Arg618 with more than one of the remaining dibasics produced proteins that reached the TGN but were not stored in secretory granules and exited the cells through the constitutive secretory pathway. These data demonstrate that the Arg617-Arg618 plays a prominent role in targeting PC1 to secretory granules.

Amino Acid Substitution↗
PubMed2006

Improving function and survival of pancreatic islets by endogenous production of glucagon-like peptide 1 (GLP-1).

Glucagon-like peptide 1 (GLP-1) is a hormone that has received significant attention as a therapy for diabetes because of its ability to stimulate insulin biosynthesis and release and to promote growth and survival of insulin-producing beta cells. While GLP-1 is produced from the proglucagon precursor by means of prohormone convertase (PC) 1/3 activity in enteroendocrine L cells, the same precursor is differentially processed by PC2 in pancreatic islet alpha cells to release glucagon, leaving GLP-1 trapped within a larger fragment with no known function. We hypothesized that we could induce GLP-1 production directly within pancreatic islets by means of delivery of PC1/3 and, further, that this intervention would improve the viability and function of islets. Here, we show that adenovirus-mediated expression of PC1/3 in alpha cells increases islet GLP-1 secretion, resulting in improved glucose-stimulated insulin secretion and enhanced survival in response to cytokine treatment. PC1/3 expression in alpha cells also improved performance after islet transplantation in a mouse model of type 1 diabetes, possibly by enhancing nuclear Pdx1 and insulin content of islet beta cells. These results demonstrate a unique strategy for liberating GLP-1 from directly within the target organ and highlight the potential for up-regulating islet GLP-1 production as a means of treating diabetes.

Adenoviridae↗
PubMed1992

The cDNA sequence of the human pro-hormone and pro-protein convertase PC1.

Using a probe consisting of the full-length cDNA sequence of the mouse pro-hormone convertase PC1 (mPC1), we isolated from a lambda gt10 human pituitary cDNA library a number of contiguous clones, of which composite sequence of 3.3-kb defined the complete coding sequence of human PC1 (hPC1). The cDNA sequence of hPC1 encodes a protein containing 753 amino acids and potentially two N-glycosylation sites, one carboxy-terminal amidation site, a cAMP-dependent protein kinase Ser phosphorylation site, a tyrosine kinase phosphorylation site, and an ArgGlyAsp (RGD) sequence. Like mPC1, the carboxy-terminal sequence of hPC1 exhibits an amphipathic domain potentially involved in membrane association. The coding region of hPC1 exhibits an overall 92.6% protein sequence identity to the mouse mPC1 sequence, with the highest homology (98%) found in the catalytic segment of the molecule (residues 84-399). Whereas Northern blot analysis of tissues obtained from mouse, rat and porcine demonstrated the presence of two mRNAs of 3 kb and 5 kb, Northern blots of human tissues and cells demonstrated the presence of a dominant transcript of 6.2 kb and the presence of smaller transcripts in some tissues. The major site of production of hPC1 seems to be the pituitary and brain, although detection was also possible in pancreas and heart.

Amino Acid Sequence↗
PubMed2000

Effects of labor on pituitary expression of proopiomelanocortin, prohormone convertase (PC)-1, PC-2, and glucocorticoid receptor mRNA in fetal sheep.

We hypothesized that the concurrent prepartum rise in adrenocorticotropic hormone (ACTH) and cortisol in the plasma of fetal sheep might be attributable to altered expression of pituitary endoproteases, prohormone convertase (PC)-1, and PC-2, or to changes in pituitary expression of glucocorticoid receptor (GR) that would influence negative feedback potential. We obtained pituitary tissue from fetal sheep during late pregnancy (d 100-d 145, term) and at precise times during the process of labor and used in situ hybridization to localize and quantify mRNA levels. Proopiomelanocortin (POMC) mRNA was regionally distributed (pars intermedia > inferior pars distalis > superior pars distalis) and increased within the pars distalis during late pregnancy and with labor. At term, levels of PC-1 and PC-2 mRNA were higher in the pars intermedia than pars distalis; PC-1 but not PC-2 in the pars distalis increased with gestational age, although it did not change further at labor. GR mRNA levels in the pars distalis increased between d 135 and term, then decreased during labor. We suggest that the concomitant rise in plasma ACTH and cortisol of fetal sheep during late gestation may be attributable, in part, to increased expression of PC-1 leading to increased POMC processing. Furthermore, the negative feedback effects of cortisol on pituitary POMC synthesis and/or ACTH release during active parturition may be lessened by downregulation of anterior pituitary GR.

Adrenocorticotropic Hormone↗
PubMed1999

Modulation of prohormone convertase 2 in spinal cord during gestation and hormone-simulated pregnancy.

Gestation as well as its hormonal simulation (HSP) is characterized by an enhanced spinal dynorphin/kappa-opioid antinociception. This antinociception is accompanied by decreased content of dynorphin precursor intermediates and increased content of mature dynorphin peptides (1-17 and 1-8) in the lumbar spinal region. This suggests that augmented processing of spinal dynorphin precursor intermediates is an adaptive mechanism used by dynorphin neurons to meet increased synthetic demands necessitated by increased dynorphin neurotransmission. Prohormone convertase (PC) 1 and 2 represent major secretory granule proteolytic processing activities capable of converting neuroendocrine and neurotransmitter peptide (dynorphin) precursor intermediates to their mature, biologically active products. Accordingly, the current investigation was undertaken to assess their potential relevance to peptidergic (dynorphin) neuronal functional plasticity in vivo. In order to evaluate a molecular biological parameter of PC2 synthesis, a solution hybridization assay was developed with which to quantify changes in the spinal lumbar content of its mRNA. This study demonstrates that during gestation and HSP, lumbar PC2 protein content, but not that of PC1, is augmented. The increase in lumbar PC2 during HSP indicates that the pregnancy blood concentration profile of 17beta-estradiol and progesterone is a predominant facet of the pregnant condition responsible for its modulation during this condition. In contrast to the elevated content of lumbar PC2 protein, levels of PC2 mRNA in the lumbar cord of pregnant or HSP rats were essentially unchanged. This indicates that increased transcriptional activity is not, necessarily, a prerequisite for increased PC2 protein content to be manifest. These observations suggest positive modulation of PC2 to be a critical component of the mechanism(s) by which spinal dynorphin neurons adapt to the demand-induced increased production of mature dynorphin peptides.

Animals↗
PubMed1994

In vitro processing of proopiomelanocortin by recombinant PC1 (SPC3).

The prohormone convertases, PC1 (SPC3) and PC2, are subtilisin-like serine proteases capable of processing neuropeptide precursors. In cotransfection experiments, other investigators have found that PC1 and PC2 can process POMC to appropriate peptide products. In this study, recombinant rat PC1 was stably expressed in a mouse L-cell line and partially purified. Mouse POMC was cleaved by recombinant PC1 to generate ACTH intermediates, ACTH, ACTH linked to joining peptide, joining peptide, 16-kilodalton N-POMC, N-POMC-(1-74), and beta-lipotropin. Recombinant PC1 was also found to cleave ACTH to ACTH-(1-15) and bovine N-POMC-(1-77) to gamma 3 MSH. The pH optimum of the cleavages was 6.0. We conclude that recombinant PC1 is capable of processing POMC in vitro at all of the paired basic residues, with the exception of Lys-Arg and Lys-Lys in beta-lipotropin and beta-endorphin, respectively. This in vitro study showed a more general specificity of recombinant PC1 for paired and tetrabasic residues of POMC than was previously found in cotransfection experiments. Other cellular regulatory mechanisms probably play a role in limiting the processing of POMC in vivo in the anterior pituitary, where gamma 3 MSH and alpha MSH are not found in significant amounts.

Adrenocorticotropic Hormone↗
PubMed1995

Ionic milieu controls the compartment-specific activation of pro-opiomelanocortin processing in AtT-20 cells.

Newly synthesized prohormones and their processing enzymes transit through the same compartments before being packaged into regulated secretory granules. Despite this coordinated intracellular transport, prohormone processing does not occur until late in the secretory pathway. In the mouse pituitary AtT-20 cell line, conversion of pro-opiomelanocortin (POMC) to mature adrenocorticotropic hormone involves the prohormone convertase PC1. The mechanism by which this proteolytic processing is restricted to late secretory compartments is unknown; PC1 activity could be regulated by compartment-specific activators/inhibitors, or through changes in the ionic milieu that influence its activity. By arresting transport in a semi-intact cell system, we have addressed whether metabolically labeled POMC trapped in early secretory compartments can be induced to undergo conversion if the ionic milieu in these compartments is experimentally manipulated. Prolonged incubation of labeled POMC trapped in the endoplasmic reticulum or Golgi/trans-Golgi network did not result in processing, thereby supporting the theory that processing is normally a post-Golgi/trans-Golgi network event. However, acidification of these compartments allowed effective processing of POMC to the intermediate and mature forms. The observed processing increased sharply at a pH below 6.0 and required millimolar calcium, regardless of the compartment in which labeled POMC resided. These conditions also resulted in the coordinate conversion of PC1 from the 84/87 kDa into the 74-kDa and 66-kDa forms. We propose that POMC processing is predominantly restricted to acidifying secretory granules, and that a change in pH within these granules is both necessary and sufficient to activate POMC processing.

Adrenocorticotropic Hormone↗
PubMed2003

Chromogranin a processing in human pituitary adenomas and carcinomas: analysis with region-specific antibodies.

The expression of various chromogranin A (CgA) peptide fragments was examined with region-specific antisera in benign and malignant pituitary tumors. Analysis of the proconvertases responsible for proteolytic processing of CgA, prohormone convertase 1/3 (PC1/3), and PC2 was also performed. Adenomas were studied using tissue microarrays, and a larger tissue section of a subset of the prolactin (PRL) adenomas was used to compare to the tissue microarray analysis. Carcinomas were analyzed using larger tissue sections. There were differences in CgA proteolytic products detected between the functional (PRL, adrenocorticotropic hormone [ACTH], and growth hormone tumors and the nonfunctional (gonadotroph and null cell) tumors, with the former group expressing lower levels of many peptides. These differences were most notable in the PRL adenomas and carcinomas in which the region-specific antisera against vasostatin I and vasostatin II detected these fragments in the lowest percentage of tumors and/or had the weakest immunoreactivity. The CgA peptide fragment detected by CgA 176-195 (chromacin) antiserum was expressed by the highest percentage of most functional and nonfunctional benign and malignant pituitary tumors. ACTH carcinomas (n = 3) were more strongly immunoreactive compared to the ACTH adenomas. These results show that there is differential expression of CgA peptide fragments and PC1/3 among different types of pituitary tumors and that ACTH pituitary carcinomas have higher levels of immunoreactive CgA peptide fragments compared to ACTH adenomas. This study also shows the utility of tissue microarrays in the analysis of a large group of tumors with regionspecific antisera.

Adenoma↗
PubMed1995

Distinct mRNA expression of the highly homologous convertases PC5 and PACE4 in the rat brain and pituitary.

Posttranslational endoproteolysis is essential for the production of biologically active peptides from inactive precursors. Six kexin/substilisin-like endoproteases have been characterized in mammalian species. To understand the complex physiological functions of each convertase within a cellular context it is necessary to comprehensively define its tissue distribution and cohabitation with other members of the family. Previous studies demonstrated the distinct distribution of PC1, PC2, and furin mRNAs in the pituitary and brain, suggesting a unique function for each enzyme. In the present study, the mRNA tissue distributions of the two most recent and homologous members, PC5 and PACE4, were analyzed in rat pituitary and brain using in situ hybridization histochemistry. In the pituitary, the anterior lobe exhibited moderate levels of PC5 and high levels of PACE4 mRNAs. The intermediate lobe showed low levels of PC5 expression, while PACE4 mRNA levels were undetectable. PACE4 transcripts were detected throughout cells of the neural lobe suggesting expression in pituicytes. In the brain, PC5 expression was more restricted than PACE4. PC5 mRNA was detected only in neuronal cells, whereas PACE4 mRNA was expressed in both neuronal and glial cells. In areas that are rich in neuropeptides such as cortex, hippocampus, and hypothalamus, mRNA levels of PC5 were high but PACE4 were low or undetectable. In regions, such as the amygdaloid body and thalamus, distinct but complementary distributions of PC5 and PACE4 mRNAs were observed. The medial habenular and cerebellar Purkinje cells expressed very high levels of PACE4 mRNA. The present data strongly suggest unique tissue-specific functions of PC5 and PACE4.

Animals↗
PubMed1991

Identification of a cDNA encoding a second putative prohormone convertase related to PC2 in AtT20 cells and islets of Langerhans.

PC2 and furin are two recently identified members of a class of mammalian proteins homologous to the yeast precursor processing protease kex2 and the bacterial subtillisins. We have used the polymerase chain reaction to identify and clone a cDNA (PC3) from the mouse AtT20 anterior pituitary cell line that represents an additional member of this growing family of mammalian proteases. PC3 encodes a 753-residue protein that begins with a signal peptide and contains a 292-residue domain closely related to the catalytic modules of PC2, furin, and kex2. Within this region 58%, 65%, and 50% of the amino acids of PC3 are identical to those of the aligned PC2, furin, and kex2 sequences, respectively, and the catalytically important Asp, His, and Ser residues are all conserved. On Northern blots, PC3 hybridizes to two transcripts of 3 and 5 kilobases. Tissue distribution studies indicate that both PC2 and PC3 are expressed in a variety of neuroendocrine tissues, including pancreatic islets and brain, but are not expressed in liver, kidney, skeletal muscle, and spleen. The high degree of similarity of PC3, PC2, and furin suggests that they are all members of a superfamily of mammalian proteases that are involved in the processing of prohormones and/or other protein precursors. In contrast to furin, PC3, like PC2, lacks a hydrophobic transmembrane anchor, but it has a potential C-terminal amphipathic helical segment similar to the putative membrane anchor of carboxypeptidase H. These and other differences suggest that these proteins carry out compartmentalized proteolysis within cells, such as processing within regulated versus constitutive secretory pathways.

Adrenal Gland Neoplasms↗
PubMed2004

Regulation of hypothalamic prohormone convertases 1 and 2 and effects on processing of prothyrotropin-releasing hormone.

Regulation of energy balance by leptin involves regulation of several neuropeptides, including thyrotropin-releasing hormone (TRH). Synthesized from a larger inactive precursor, its maturation requires proteolytic cleavage by prohormone convertases 1 and 2 (PC1 and PC2). Since this maturation in response to leptin requires prohormone processing, we hypothesized that leptin might regulate hypothalamic PC1 and PC2 expression, ultimately leading to coordinated processing of prohormones into mature peptides. Using hypothalamic neurons, we found that leptin stimulated PC1 and PC2 mRNA and protein expression and also increased PC1 and PC2 promoter activities in transfected 293T cells. Starvation of rats, leading to low serum leptin levels, decreased PC1 and PC2 gene and protein expression in the paraventricular nucleus (PVN) of the hypothalamus. Exogenous administration of leptin to fasted animals restored PC1 levels in the median eminence (ME) and the PVN to approximately the level found in fed control animals. Consistent with this regulation of PCs in the PVN, concentrations of TRH in the PVN and ME were substantially reduced in the fasted animals relative to the fed animals, and leptin reversed this decrease. Further analysis showed that proteolytic cleavage of pro-thyrotropin-releasing hormone (proTRH) at known PC cleavage sites was reduced by fasting and increased in animals given leptin. Combined, these findings suggest that leptin-dependent stimulation of hypothalamic TRH expression involves both activation of trh transcription and stimulation of PC1 and PC2 expression, which lead to enhanced processing of proTRH into mature TRH.

Animals↗
PubMed1997

Immunocytochemical localization of prohormone convertases PC1 and PC2 in the anuran pituitary gland: subcellular localization in corticotrope and melanotrope cells.

Specific antisera against mammalian prohormone convertases PC1 and PC2 have been used to examine, light-immunocytochemically, the distribution of these enzymes in the pituitary gland of five different species of anuran amphibians (Rana catesbeiana, Bufo japonicus formosus, Xenopus laevis, Rana brevipoda porosa, and Buergeria japonica). A differential pattern of immunoreactivity of PC1 and PC2 was found among these species. Only PC1 was found in the corticotrope cells of the pars distalis in R. catesbeiana, B. japonicus formosus, and X. laevis. Only PC2 was observed in these cells in B. japonica, whereas both PC1 and PC2 were present in these cells in R. brevipoda porosa. PC2 immunoreactivity was always observed in melanotrope cells in the pars intermedia of all of the species, but it coexisted with PC1 immunoreactivity only in R. catesbeiana and X. laevis. The nerve fibers and terminals in the pars nervosa in all of the species were intensely immunopositive with both PC1 and PC2 antibodies. Immunoelectron microscopy on B. japonicus formosus and B. japonica, by means of double-labeling with gold particles of different sizes, revealed that almost all the adrenocorticotropin-positive secretory granules in the corticotrope cells and alpha-melanophore-stimulating-hormone-positive secretory granules in the melanotrope cells were also labeled with either PC1 or PC2 antibodies. This study suggests that PC1 and PC2 are involved in the intracellular proteolytic cleavage of proopiomelanocortin in amphibian pituitary glands, a situation similar to that proposed for mammals.

Adrenocorticotropic Hormone↗