Testis-specific prohormone convertase PC4 processes the precursor of pituitary adenylate cyclase-activating polypeptide (PACAP)

Discovery and In Vitro Characterization of BAY 2686013, an Allosteric Small Molecule Antagonist of the Human Pituitary Adenylate Cyclase-Activating Polypeptide Receptor

The human pituitary adenylate cyclase-activating polypeptide receptor (hPAC1-R), a class B G-protein-coupled receptor (GPCR) identified almost 30 years ago, represents an important pharmacological target in the areas of neuroscience, oncology, and immunology. Despite interest in this target, only a very limited number of small molecule modulators have been reported for this receptor. We herein describe the results of a drug discovery program aiming for the identification of a potent and selective hPAC1-R antagonist. An initial high-throughput screening (HTS) screen of 3.05 million compounds originating from the Bayer screening library failed to identify any tractable hits. A second, completely revised screen using native human embryonic kidney (HEK)293 cells yielded a small number of hits exhibiting antagonistic properties (4.2 million compounds screened). BAY 2686013 (1) emerged as a promising compound showing selective antagonistic activity in the submicromolar potency range. In-depth characterization supported the hypothesis that BAY 2686013 blocks receptor activity in a noncompetitive manner. Preclinical, pharmacokinetic profiling indicates that BAY 2686013 is a valuable tool compound for better understanding the signaling and function of hPAC1-R. SIGNIFICANCE STATEMENT: Although the human pituitary adenylate cyclase-activating polypeptide receptor (hPAC1-R) is of major significance as a therapeutic target with a well documented role in pain signaling, only a very limited number of small-molecule (SMOL) compounds are known to modulate its activity. We identified and thoroughly characterized a novel, potent, and selective SMOL antagonist of hPAC1-R (acting in an allosteric manner). These characteristics make BAY 2686013 an ideal tool for further studies.

Effect of PACAP/PAC1R on Follicle Development of Djungarian Hamster (Phodopus sungorus) with the Variation of Ambient Temperatures

In Phodopus sungorus, the relationship between pituitary adenylate cyclase-activating polypeptide (PACAP) and its receptor (PAC1R), follicle-stimulating hormone (FSH), and follicle development remains unclear. In this study, we found that the development of growing follicles and antral follicles were inhibited at low (8 °C, 14 °C) and high (29 °C) temperatures. Meanwhile, PACAP/PAC1R expression and follicle-stimulating hormone (FSH) serum concentration significantly decreased during ambient temperatures of 8 °C, 14 °C and 29 °C compared to 21 °C. Thus, ambient temperature may influence the expression of PACAP/PAC1R and the synthesis of FSH for involvement in follicle development. Moreover, PACAP/PAC1R had major functional elements including PKA/PKG and PKC phosphorylation sites, which may involve in the pathway of FSH synthesis through cAMP-PKA and its downstream signal pathway. Moreover, there was a significant positive correlation between the expression levels of PACAP/PAC1R and the number of the growing and antral follicles, as well as the serum FSH concentration and the number of antral follicles. However, there was no significant correlation between the expression levels of PACAP/PAC1R and the serum FSH concentration, indicating a complicated pathway between PACAP/PAC1R and FSH. In conclusion, ambient temperature affects the expression of PACAP/PAC1R and the serum FSH concentration. The expression of PACAP/PAC1R and the serum FSH concentration are correlated with follicle development, which implies that they are involved in follicle development, which will ultimately influence the reproduction of Phodopus sungorus. This study can lay the foundation for future investigation on the regulation mechanism of reproduction in Phodopus sungorus.

Protease propeptide structures, mechanisms of activation, and functions

Proteases are a diverse group of hydrolytic enzymes, ranging from single-domain catalytic molecules to sophisticated multi-functional macromolecules. Human proteases are divided into five mechanistic classes: aspartate, cysteine, metallo, serine and threonine proteases, based on the catalytic mechanism of hydrolysis. As a protective mechanism against uncontrolled proteolysis, proteases are often produced and secreted as inactive precursors, called zymogens, containing inhibitory N-terminal propeptides. Protease propeptide structures vary considerably in length, ranging from dipeptides and propeptides of about 10 amino acids to complex multifunctional prodomains with hundreds of residues. Interestingly, sequence analysis of the different protease domains has demonstrated that propeptide sequences present higher heterogeneity compared with their catalytic domains. Therefore, we suggest that protease inhibition targeting propeptides might be more specific and have less off-target effects than classical inhibitors. The roles of propeptides, besides keeping protease latency, include correct folding of proteases, compartmentalization, liganding, and functional modulation. Changes in the propeptide sequence, thus, have a tremendous impact on the cognate enzymes. Small modifications of the propeptide sequences modulate the activity of the enzymes, which may be useful as a therapeutic strategy. This review provides an overview of known human proteases, with a focus on the role of their propeptides. We review propeptide functions, activation mechanisms, and possible therapeutic applications.

Discovery of PACAP and its receptors in the brain

Pituitary adenylate-cyclase-activating polypeptide (PACAP) is a 27- or 38-amino acid neuropeptide, which belongs to the vasoactive intestinal polypeptide (VIP)/glucagon/secretin family. PACAP shows particularly high homology (~ 68%) to VIP. Because of the high homology of the amino acid sequences of PACAP and VIP, these peptides share three class B-G-protein coupled receptors: the PAC1-Receptor (PAC1-R), the VPAC1-Receptor (VPAC1-R) and VPAC2-Receptor (VPAC2-R). These receptors have high homology to each other, and their high homology is utilized for these discoveries. This review provides mainly an overview of the history of the discovery of PACAP and its three receptors.

Proteolytic Cleavage-Mechanisms, Function, and "Omic" Approaches for a Near-Ubiquitous Posttranslational Modification

Proteases enzymatically hydrolyze peptide bonds in substrate proteins, resulting in a widespread, irreversible posttranslational modification of the protein's structure and biological function. Often regarded as a mere degradative mechanism in destruction of proteins or turnover in maintaining physiological homeostasis, recent research in the field of degradomics has led to the recognition of two main yet unexpected concepts. First, that targeted, limited proteolytic cleavage events by a wide repertoire of proteases are pivotal regulators of most, if not all, physiological and pathological processes. Second, an unexpected in vivo abundance of stable cleaved proteins revealed pervasive, functionally relevant protein processing in normal and diseased tissue-from 40 to 70% of proteins also occur in vivo as distinct stable proteoforms with undocumented N- or C-termini, meaning these proteoforms are stable functional cleavage products, most with unknown functional implications. In this Review, we discuss the structural biology aspects and mechanisms of catalysis by different protease classes. We also provide an overview of biological pathways that utilize specific proteolytic cleavage as a precision control mechanism in protein quality control, stability, localization, and maturation, as well as proteolytic cleavage as a mediator in signaling pathways. Lastly, we provide a comprehensive overview of analytical methods and approaches to study activity and substrates of proteolytic enzymes in relevant biological models, both historical and focusing on state of the art proteomics techniques in the field of degradomics research.

VIP and PACAP

Vasoactive intestinal polypeptide (VIP) is derived from a 170 amino acid precursor which in addition is processed to preproVIP 22-79, PHI, preproVIP 111-122 and preproVIP 156-170. All preproVIP-derived peptides have been shown in normal tissue and VIP-producing cell lines and elevated quantities occur in plasma and tumour tissues from patients with VIP-producing tumours. In some tissues the dibasic cleavage site after PHI is uncleaved resulting in a C-terminally extended form, PHV. PHI and VIP are present in a 1:1 molar ratio in large dense core vesicles and released in roughly equimolar amounts. Carboxyamidation of VIP and PHI is not critical and glycine-extended forms of both peptides have been demonstrated. Pituitary adenylate cyclase activating polypeptide (PACAP) is derived from a 170 amino acid long precursor, which gives rise to PACAP 38, PACAP 27 and PACAP related peptide (PRP). All peptides are present in tissue, the dominating form being PACAP 38. Prohormone convertase (PC) 1 and 2 seem to be involved in the processing of PACAP, except in the testes and ovary, where the PACAP precursor is substrate for PC4.

The role of PACAP in central cardiorespiratory regulation

Pituitary adenylate cyclase activating polypeptide (PACAP) plays a role in almost every biological process from reproduction to hippocampal function. One area where a role for PACAP is not clearly delineated is central cardiorespiratory regulation. PACAP and its receptors (PAC1, VPAC1 and VPAC2) are present in cardiovascular areas of the ventral medulla and spinal cord and in the periphery. Central administration of PACAP generally increases arterial pressure. Knowledge about the role of PACAP in central cardiovascular regulation is growing, but even less is known about PACAP in central respiratory regulation. No specific data is currently available regarding the presence of PACAP or receptors in key respiratory centers, although it is known that neonatal PACAP knock-out mice die suddenly in a manner similar to sudden infant death syndrome (SIDS). Future studies in mature preparations investigating the role of PACAP in the physiology and integration of central cardiorespiratory reflexes are clearly essential for a full understanding of this important neuropeptide in breathing.

GnRH stimulates expression of PACAP in the pituitary gonadotropes via both the PKA and PKC signaling systems

Recent studies have demonstrated a clear role for pituitary adenylate cyclase-activating polypeptide (PACAP) in the regulation of gonadotropin biosynthesis and secretion, both alone and in conjunction with GnRH. First defined as a hypothalamic releasing factor, PACAP subsequently has been identified in the gonadotrope subpopulation of the anterior pituitary gland, suggesting that PACAP may act as an autocrine-paracrine factor in this tissue. In initial studies, we determined that GnRH markedly stimulated endogenous PACAP mRNA levels and promoter-reporter activity in the mature gonadotrope cell line, LbetaT2. GnRH-stimulated rat PACAP promoter activity was blunted with deletion from position -915 to -402 and eliminated with further truncation to position -77 relative to the transcriptional start site. Site-directed mutagenesis demonstrated a functional requirement for a cAMP response element (CRE)-like site at position -205 and an activating protein-1 (AP-1)-like site at position -275, both of which bound CRE binding protein and AP-1 family members on EMSA. Treatment with pharmacological activators or inhibitors of second messenger signaling pathways implicated the protein kinase A, protein kinase C, and MAPK pathways in the GnRH response. In support of these in vitro data, we demonstrate that JunB binds to the rat PACAP gene promoter by chromatin immunoprecipitation assay and that small interfering RNA knockdown of JunB, cFos, and CRE binding protein factors blunts PACAP expression. In summary, these results further elucidate the complex functional interactions between PACAP and GnRH in the anterior pituitary. Specifically, these studies demonstrate that GnRH-stimulated PACAP gene expression is mediated via multiple signaling pathways acting on CRE/AP-1 sites in the proximal gene promoter. Because both PACAP and GnRH regulate gonadotropin biosynthesis and secretion, these results provide important insight into the critical fine tuning of gonadotrope function and, thereby, the maintenance of normal reproductive function.

Intravenous infusion of pituitary adenylate cyclase-activating polypeptide (PACAP) in a patient with multiple myeloma and myeloma kidney: a case study

We have recently shown significant renoprotective effects with the administration of pituitary adenylate cyclase-activating polypeptide (PACAP) in models of myeloma kidney. PACAP markedly inhibited the production of proinflammatory cytokines stimulated by immunoglobulin light chains in human renal proximal tubule epithelial cells and in the kidneys of rats infused with myeloma light chains. PACAP was also shown to suppress the proliferation of human kappa and lambda light chain-secreting multiple myeloma-derived cells. In this case study, an 81-year-old male patient with active multiple myeloma and myeloma kidney was infused intravenously with synthetic human PACAP38 at a rate of 4 pmol/kg/min for 120 min. The continuous infusion increased the level of PACAP38 in blood, with a plateau at about 0.2 nM during the infusion. The level of PACAP in the blood rapidly declined after the cessation of administration with a half-life of about 5-10 min. The continuous infusion did not significantly alter the basal glucose level, blood gases or blood pressure. There was a large reduction in free lambda light chains in urine after the start of the treatment with PACAP. These studies show that PACAP can be safely used in humans and suggest that it could be used as a novel therapeutic agent for the treatment of multiple myeloma and myeloma kidney.

Localization, characterization and function of pituitary adenylate cyclase-activating polypeptide during brain development

Neural development is controlled by region-specific factors that regulate cell proliferation, migration and differentiation. Pituitary adenylate cyclase-activating polypeptide (PACAP) is a neuropeptide that exerts a wide range of effects on different cell types in the brain as early as the fetal stage. Here we review current knowledge concerning several aspects of PACAP expression in embryonic and neonatal neural tissue: (i) the distribution of PACAP and PACAP receptors mRNA in the developing brain; (ii) the characteristic generation of neurons, astrocytes and oligodendrocytes in brain areas where the PACAP receptor is expressed and (iii) the role of PACAP as a regulator of neural development, inducing differentiation and proliferation in association with other trophic factors or signal transduction molecules.

Pituitary adenylate cyclase-activating polypeptide (PACAP)-like immunoreactivity in the brain of a teleost, Uranoscopus japonicus: immunohistochemical relationship between PACAP and adenohypophysial hormones

The neuropeptide pituitary adenylate cyclase-activating polypeptide (PACAP) could play a role in stimulating pituitary hormone release in fish brain. In this study, we used immunochemical techniques to examine the histological and quantitative distribution of PACAP in the central nervous system (CNS) of a teleost, the stargazer, Uranoscopus japonicus. In addition, high performance liquid chromatographic (HPLC) analysis was performed to characterize the form of PACAP present, while the relationship between PACAP and adenohypophysial hormones was also determined immunohistochemically. PACAP-like immunoreactive (LI) neuronal cell bodies and fibers were found not only in the hypothalamo-pituitary region but also in the midbrain and hindbrain regions. PACAP-LI fibers were identified in the neurohypophysis in close proximity to pituitary cells containing immunoreactive hormones such as somatolactin, the N-terminal peptide of proopiomelanocortin, and N-acetyl endorphin. The concentration of immunoreactive PACAP in whole brain tissue was approximately 300 pmol/g wet weight. The average concentrations of immunoreactive PACAP in regions of the telencephalon, diencephalon, tectum, cerebellum, and rhombencephalon were 217.53, 510.26, 83.30, 148.64, and 364.62 pmol/g, respectively. In reverse-phase HPLC experiments, the predominant form of immunoreactive PACAP eluted closely with synthetic stargazer PACAP38, while PACAP27-like immunoreactivity was negligible. These results suggest that PACAP38 is the predominant PACAP form in the stargazer CNS, and that PACAP acts not only as a hypophysiotropic factor for adenohypophysial hormone release but also as a neurotransmitter and neuromodulator in the CNS.

In vitro elucidation of substrate specificity and bioassay of proprotein convertase 4 using intramolecularly quenched fluorogenic peptides

The fourth member of Ca2+-dependent mammalian secretory subtilase, PC4 (proprotein convertase 4), is primarily expressed in testicular germ cell and ovarian macrophage. Its role in sperm fertilization and in early embryonic development has been demonstrated earlier through several studies, including those with PC4 null mice. A number of physiological substrates found in reproductive tissues have been postulated or identified for PC4 by various biochemical studies. These include growth factors IGF-1 (insulin-like growth factor-1) and IGF-2, hormonal polypeptide proPACAP (where PACAP stands for pituitary adenylate cyclase-activating polypeptide) and a number of surface proteins of ADAM (ADisintegrin And Metalloproteinase-like) family such as ADAM-1 (fertilin a), ADAM-2 (fertilin b), ADAM-3 (procyritestin) and ADAM-5. To provide further evidence in support of this notion and also to study the substrate specificity and bioassay of PC4, a series of intramolecularly quenched fluorogenic peptides containing the cleavage sites and several mutants were prepared. A comparative kinetic analysis and measurement of Vmax (app)/Km (app) ratio of these fluorogenic substrates against PC4 and PC7 revealed that the mutant variants of h (human) proPACAP and m (mouse) ADAM-5 derived peptides Q-PACAP141-151-mutant [Abz-141RVKNKGRRI150P151SY(NO2)-A-CONH2] (150A151Y replaced by PS) and Q-ADAM-5380-388-mutant [Abz-380E381PKPARRP388RY(NO2)A-CONH2] (381R replaced by P) are most efficiently and selectively cleaved by PC4. Using these two and Q-IGF-263-71 peptides, we showed that the sperm extract of normal adult mice is much higher when compared with that of PC4-null mice. This suggests that these fluorogenic peptides are useful for specific bioassay of PC4 activity. In addition, kinetic studies with various peptidyl-MCA indicate that the hexapeptide Ac-KTKQLR-MCA (where MCA stands for 4-methyl coumaryl-7-amide) is most efficiently and selectively cleaved by PC4 at RMCA, making it another effective agent for bioassay of PC4 activity. The study concludes that the most probable sequence motif for recognition by PC4 is KXKXXR or KXXR, where X is any amino acid other than cysteine and that it prefers proline at P3, P5 and/or P2' positions. It was also revealed that PC4 is a good candidate processing enzyme for growth factors IGF-1 and -2, neuropeptide proPACAP and several ADAM proteins such as ADAM-1, -2, -3 and -5.

Pituitary adenylate cyclase activating polypeptide-mediated intracrine signaling in the testicular germ cells

Pituitary adenylate cyclase activating polypeptide (PACAP) is found not only in the brain, but is also abundantly expressed in the testicular germ cells. However, the physiological role of testicular PACAP remains unknown. Autoradiographic studies showed a considerable number of PACAP-specific binding sites in the seminiferous tubules. Immunohistochemistry demonstrated PAC1-receptor (R)-like immunoreactivity (li) in the cytoplasm of round spermatids, aggregated in the acrosome and coexpressed with PACAP-li. Spermatid-enriched fractions were examined for the subcellular localization of PACAP binding sites and PAC1-R-li. The highest levels of PACAP binding sites and PAC1-R-li were found in the cytosolic, followed by the nuclear, and the lowest levels in the membrane fraction. The testicular cytosolic PAC1-R-like protein showed a specific competitive inhibition in the radio-receptor assay for PACAP38 and 27, with a Ki of 0.069 nM and 0.179 nM, respectively. The addition of PACAP to the cytosol of spermatids only slightly activated adenylate cyclase, while it markedly stimulated the expression and activation of ERK-type mitogen-activated protein kinase (MAPK). In the PAC1-R-like protein-depleted cytosol, a PAC1-R-specific agonist, maxadilan, did not activate MAPK, but PACAP and VIP still did. Because VPAC2-R, which binds both PACAP and VIP, is expressed in the testis, the findings suggest that cytosolic VPAC2-R-like proteins are also present and coupled to MAPK. The MAPK activation does not seem to require a heterotrimeric G-protein. Because PACAP and its receptors are coexpressed in the cytoplasm of spermatids, endogenous PACAP may directly interact with the cytosolic PAC1-R-like protein without the ligand being released into the extracellular space. This possibility is supported by the observation that cytosolic endogenous PACAP in spermatids was co-immunoprecipitated with the cytosolic PAC1-R. This mechanism may be called "intracrine," and its physiological significance is discussed.

Neuropeptides of the pituitary adenylate cyclase-activating polypeptide/vasoactive intestinal polypeptide/growth hormone-releasing hormone/secretin family in testis

Mammalian testicular development and the maintenance of spermatogenesis are hormone-dependent processes that are controlled by the pituitary gonadotropins and testosterone. Recent studies have demonstrated the presence of many neuropeptides and their receptors in the testis, suggesting that these peptides operate as local regulators of testicular germ cell development and function. Among these testicular neuropeptides, the peptides that belong to the pituitary adenylate cyclase-activating polypeptide (PACAP) family, particularly growth hormone-releasing hormone and secretin, appear to show some unique common features in terms of intratesticular localization and the time of expression during the spermatogenic cycle. However, their precise physiologic roles and mechanisms of action remain unknown. This review analyzes the available information on the functional interactions among the testicular cells that appear to be mediated by locally produced neuropeptides, with a special emphasis on the peptides of the PACAP family.

Neuropeptides of the pituitary adenylate cyclase-activating polypeptide/vasoactive intestinal polypeptide/growth hormone-releasing hormone/secretin family in testis

Mammalian testicular development and the maintenance of spermatogenesis are hormone-dependent processes that are controlled by the pituitary gonadotropins and testosterone. Recent studies have demonstrated the presence of many neuropeptides and their receptors in the testis, suggesting that these peptides operate as local regulators of testicular germ cell development and function. Among these testicular neuropeptides, the peptides that belong to the pituitary adenylate cyclase-activating polypeptide (PACAP) family, particularly growth hormone-releasing hormone and secretin, appear to show some unique common features in terms of intratesticular localization and the time of expression during the spermatogenic cycle. However, their precise physiologic roles and mechanisms of action remain unknown. This review analyzes the available information on the functional interactions among the testicular cells that appear to be mediated by locally produced neuropeptides, with a special emphasis on the peptides of the PACAP family.

Expression and distribution of pituitary adenylate cyclase-activating peptide in human prostate and prostate cancer tissues

The presence, expression and distribution of pituitary adenylate cyclase-activating peptide (PACAP) in human prostate cancer and healthy tissue were investigated by means of biochemical and morphological procedures. Reverse transcription-polymerase chain reaction (RT-PCR) analysis demonstrated the presence of its precursor encoding mRNA in both normal and pathological conditions (amplification products with 577 or 226 bp were identified). Immunochemistry using an appropriate antibody served to detect in both classes of tissues a 19.9-kDa product corresponding to the PACAP preproprotein and another protein of 14.6 kDa that may represent a product partially processed by convertases. However, a 5-kDa band characteristic of PACAP-38 peptide was not observed. Immunohistochemistry on tissue sections indicated the location of PACAP in the epithelial layer of prostate glands (and in some scarce leucocytes) but not in the stroma, either in normal or carcinomatous tissues. No clear differences could be established when comparing samples from patients with different tumor Gleason grades. These results are the first demonstration of the localization of PACAP or its precursors and its mRNA in the human prostate gland and their presence during the progression of prostate carcinoma.

A newly developed enzyme-immunoassay for measuring the tissue contents of PACAP in fish

We have developed a novel and easy enzyme-immunoassay (EIA) for pituitary adenylate cyclase-activating polypeptide (PACAP). We used it to determine immunoreactive PACAP levels in the central nervous system (CNS) and peripheral tissues of two fishes, a teleost (the stargazer) and an elasmobranch (a stingray). An antiserum was raised in a white rabbit immunized with a conjugate of synthetic stargazer PACAP27 plus keyhole limpet hemocyanin. The EIA system used an antiserum/biotin-labeled PACAP/avidin/biotin-conjugated enzyme complex, and a double antibody method was used to precipitate the immune complexes. We call the system the avidin-biotin complex detectable EIA (ABCDEIA) for PACAP. ABCDEIA with biotin-labeled PACAP27 detected only PACAP27, recognizing neither the longer forms of PACAP nor any other peptides. PACAPs with 27, 38, and 44 residues cross-reacted in another ABCDEIA with biotin-labeled PACAP38 or PACAP44. Whole brains of both fishes contained much higher levels of PACAP, 6-30 times as high as the levels in the mammalian brain, but unexpectedly, no immunoreactive PACAP27 was found in any CNS or peripheral tissue in either fish. The gastrointestinal tracts of fish also contained lower, but significant amounts of PACAP.

The testicular germ-cell protease PC4 is also expressed in macrophage-like cells of the ovary

PC4 is a serine protease primarily expressed in spermatids. We have produced PC4-deficient mice carrying an insertion of the bacterial gene for beta galactosidase under the PC4 gene promoter. Male mice lacking PC4 (-/-) exhibit severely reduced fertility. Surprisingly, the fertility of female mice is also significantly diminished in these mutants (Mbikay et al., 1997. Proc. Natl. Acad. Sci. USA 94, 6842-6846). The aim of this study was to determine the site of PC4 expression in mouse ovaries. Using a histoenzymatic assay for beta-galactosidase, we show that the PC4 promoter can drive strong expression of this enzyme in the theca-interstitium and in degenerating corpora lutea of +/- ovaries. We also demonstrate that PC4 transcripts can be detected by RT-PCR in the ovaries of +/- and +/+ mice, but not in those of -/- mice. The cells expressing PC4 were macrophage-like, since they expressed the macrophage markers CD11b and F4/80, as well as interleukin 1beta and tumor necrosis factor alpha (TNFalpha). Expression of PC4 was also detected in the mouse macrophage RAW264.7 cell line. Interestingly, TNFalpha transcripts were 3-fold more abundant in ovarian macrophage-like cells from -/- mice than in those from +/+ mice, suggesting a constitutive state of activation of the mutant cells. An inverse relationship between PC4 expression and macrophage activation was also observed in RAW264.7 cells. When these cells were activated using bacterial lipopolysaccharide, the level of PC4 transcripts decreased, while that of TNFalpha increased. These observations identify PC4 as an enzyme that could influence ovarian physiology by affecting macrophage functions.

The origin and function of the pituitary adenylate cyclase-activating polypeptide (PACAP)/glucagon superfamily

The pituitary adenylate cyclase-activating polypeptide (PACAP)/ glucagon superfamily includes nine hormones in humans that are related by structure, distribution (especially the brain and gut), function (often by activation of cAMP), and receptors (a subset of seven-transmembrane receptors). The nine hormones include glucagon, glucagon-like peptide-1 (GLP-1), GLP-2, glucose-dependent insulinotropic polypeptide (GIP), GH-releasing hormone (GRF), peptide histidine-methionine (PHM), PACAP, secretin, and vasoactive intestinal polypeptide (VIP). The origin of the ancestral superfamily members is at least as old as the invertebrates; the most ancient and tightly conserved members are PACAP and glucagon. Evidence to date suggests the superfamily began with a gene or exon duplication and then continued to diverge with some gene duplications in vertebrates. The function of PACAP is considered in detail because it is newly (1989) discovered; it is tightly conserved (96% over 700 million years); and it is probably the ancestral molecule. The diverse functions of PACAP include regulation of proliferation, differentiation, and apoptosis in some cell populations. In addition, PACAP regulates metabolism and the cardiovascular, endocrine, and immune systems, although the physiological event(s) that coordinates PACAP responses remains to be identified.

Pituitary adenylate cyclase-activating polypeptide precursor is processed solely by prohormone convertase 4 in the gonads

Pituitary adenylate cyclase-activating polypeptide (PACAP) is abundant not only in the brain, but also in the testis. Immunohistochemical studies have shown that PACAP-LI in rat testis is expressed stage specifically in spermatids. This suggests that testicular PACAP participates in the regulatory mechanism of spermatogenesis. Additionally, the ovary contains a relatively small amount of PACAP, conceivably involved in the regulation of folliculogenesis. PACAP is synthesized as a preprohormone and is processed by prohormone convertases, such as PC1, PC2, and PC4. PC4 is expressed only in the testis and ovary, where neither PC1 nor PC2 is expressed. However, whether PC4 is the sole endoprotease for the PACAP precursor in the gonads remains unknown. Recent studies using PC4-transgenic mice revealed that male PC4-null mice exhibited severely impaired fertility, although spermatogenesis appeared to be normal. The female PC4-null mice exhibited delayed folliculogenesis in the ovaries. To examine whether PC4 is the sole processing enzyme for the PACAP precursor in the gonads, we analyzed testicular and ovarian extracts from the PC4-null and wild-type mice for PACAP (PACAP38 and PACAP27) and its messenger RNA using reverse phase HPLC combined with specific RIAs and ribonuclease protection assay, respectively. For RIAs, three different polyclonal antisera with different recognition sites were used to identify PACAP38, PACAP27, and its precursor. Neither the testis nor the ovary from the PC4-null mice expressed PACAP38 or PACAP27, but the levels of PACAP transcripts in the testis and ovary of homozygous PC4-deficient mice were considerably elevated compared with those of the wild-type and heterozygous animals. The findings indicate that PC4 is the sole processing enzyme for the precursor of PACAP in the testis and ovary of mice. The possibility that the absence of bioactive PACAP in the testis and ovary of PC4-null mice caused severely impaired fertility in the males and delayed folliculogenesis in females warrants investigation.

Peptide hormone precursor processing: getting sorted?

Processing of proproteins to biologically active peptides and, in the case of peptide hormones and neuropeptides, their sorting to granules of the regulated secretory pathway, requires the concerted action of a cascade of enzymes and chaperones. The purpose of this review is to summarize the recent emerging knowledge of how these molecules affect specific endocrine systems. This has come about through the study of gene knockout mice as well as endocrinopathies resulting from mutated genes in humans.

Alternative splicing creates sex-specific transcripts and truncated forms of the furin protease in the parasite Dirofilaria immitis

Many extracellular proteins are activated by specific cleavage with an endoprotease. In nematodes, several proteins are cleaved after RX(K/R)R, the recognition site for the subtilisin-like proprotein convertases, furin and blisterase. To characterize furin in the parasitic nematode Dirofilaria immitis, we determined the sequence of the difur gene and its multiple transcripts. The gene spans 11 kb; encodes 16 exons and has a complex pattern of alternative splicing which generates at least 16 distinct mRNAs. The major transcript is a 4.4 kb mRNA which codes for a protein of 834 aa with an unusually long prodomain of 254 aa. Sex-specific splice variants of difur were observed by RT-PCR. The three female-specific and five male-specific transcripts are the first reported examples of sex-specific splicing in parasitic nematodes. This suggests that nematodes have sex-specific factors which regulate RNA splicing. Other splice variants are predicted to alter the phosphorylation and localization of the protease. Alternative splicing after the prodomain encodes a truncated protein that may be an inhibitor and/or substrate of Difurin.