Isolation and functional expression of human pancreatic peptidylglycine alpha-amidating monooxygenase

Isolation and characterization of a glycine-extended form of calcitonin receptor-stimulating peptide-1: another biologically active form of calcitonin receptor-stimulating peptide-1

In this study, we isolated a peptide eliciting a potent stimulatory effect on cAMP production in LLC-PK(1) cells from acid extracts of porcine brain. By structural analysis, this peptide was determined to be a C-terminal glycine-extended form of calcitonin receptor-stimulating peptide-1 (CRSP-1-Gly). Synthetic CRSP-1-Gly enhanced the cAMP production in COS-7 cells expressing calcitonin (CT) receptor as strongly as CRSP-1. Measurement of immunoreactive (IR) CRSP-1-Gly by radioimmunoassay using the specific antisera against CRSP-1-Gly showed that a relatively high level (>1pmol/g wet weight) of IR-CRSP-1-Gly was detected in the midbrain, hypothalamus, anterior and posterior lobes of pituitary, and thyroid gland, and the ratio of IR-CRSP-1-Gly to total IR-CRSP-1 varies from 0.02 to 0.35 in each tissue. These results suggest that CRSP-1-Gly is actually present in the tissues as one of major endogenous molecular forms of CRSP-1, and can regulate the cells expressing the CT receptor both in the central nervous system and peripheral tissues in a manner similar to that of CRSP-1. IR-CRSP-2 and IR-CRSP-3 are also present in the brain and other tissues, but their tissue concentrations are 33% on average and less than 3% that of total IR-CRSP-1, respectively.

Androgen-independent expression of adrenomedullin and peptidylglycine alpha-amidating monooxygenase in human prostatic carcinoma

Most of the locally advanced and metastatic prostate carcinomas (PCs) treated with antiandrogenic therapy eventually become refractory to this treatment. Locally produced factors may control prostate tumor biology after androgen withdrawal. Adrenomedullin (AM) is expressed in the prostate and could control cell growth in androgen-independent conditions. AM needs to be amidated by the enzyme peptidylglycine alpha-amidating monooxygenase (PAM) to become fully active. The objective of the present study was to analyze whether the expression of preproadrenomedullin (preproAM) and PAM in PC is regulated by androgens. For this purpose, human in vitro and in vivo PC models were grown in the presence or absence of androgens, and the expression of AM and PAM was examined by immunohistochemistry, Western blotting, RT-PCR, and Northern blotting. Furthermore, immunohistochemical analysis of AM in clinical specimens was performed to test if its expression is related to Gleason score and antiandrogenic therapy. In PC cell lines and xenografts, mRNA and protein AM levels were similar in the presence or absence of androgens. PAM expression seemed to be induced by androgen-withdrawal. Our results in clinical samples showed no relationship between AM expression and Gleason score or antiandrogenic treatment. In conclusion, our results demonstrate that preproAM and PAM expression in the human prostate is androgen-independent. In addition, we also report for the first time the expression of a novel PAM transcript in PC, which has not been previously described in other tissues.

Expression and characterization of human bifunctional peptidylglycine alpha-amidating monooxygenase

We report the purification and characterization of human bifunctional peptidylglycine alpha-amidating monooxygenase (the bifunctional PAM) expressed in Chinese hamster ovary cells. PAM is in charge of the formation of the C-terminal amides of biologically active peptides. The bifunctional PAM possesses two catalytic domains in a single polypeptide, peptidylglycine alpha-hydroxylating monooxygenase (PHM, EC 1.14.17.3) and peptidylamidoglycolate lyase (PAL, EC 4.3.2.5). By introducing a stop codon at 835 Glu, we were able to eliminate the membrane-spanning domain in the C-terminal region and succeeded in purifying a soluble form of bifunctional PAM that was secreted into the medium. Through a three-step purification procedure, we obtained 0.3mg of the purified PAM, which showed a single band at 91 kDa on SDS-PAGE, from 1L of monolayer culture medium. Metals contained in the purified PAM were analyzed and chemical modifications were performed to gain insight into the mechanism of the PAL reaction. Inductively coupled plasma detected 0.62 mol of Zn(2+) and 1.25 mol of Cu(2+) per mol of bifunctional PAM. Further, the addition of 1mM EDTA reduced the PAL activity by about 50%, but the decreased activity was recovered by the addition of an excess amount of Zn(2+). In a series of chemical modifications, phenylglyoxal almost completely eliminated the PAL activity and diethyl pyrocarbonate suppressed activity by more than 70%. These findings implied that Arg and His residues might play crucial roles during catalysis.

Immunocytochemical finding of the amidating enzymes in mouse pancreatic A-, B-, and D-cells: a comparison with human and rat

alpha-Amidation is catalyzed by two enzymatic activities, peptidyl-glycine alpha-hydroxylating mono-oxygenase (PHM) and peptidyl-alpha-hydroxyglycine alpha-amidating lyase (PAL), denoted collectively as peptidyl-glycine alpha-amidating mono-oxygenase (PAM), which also may include transmembrane and cytoplasmic domains. PAM is present in mammalian pancreas, where it appears to be abundant in the perinatal period. Nevertheless, there is no agreement on the cell type(s) that produces PAM or even on its presence in adults. In the present study we found PAM (PHM and cytoplasmic domain) immunoreactivity (IR) in A-, B-, and D-cells of adult mouse pancreas. In contrast to previous reports, PAM IR was found in B-cells of human and rat. Most of the B/D-cells were PAM immunoreactive, although with variable intensity, whereas less than half of A-cells displayed IR. Immunocytochemistry and Western blotting suggested the existence of different PAM molecules. Differences in the cellular distribution of IR for PAM domains were also observed. Whereas PHM-IR was extended throughout the cytoplasm in the three cell types, presumably in the secretory granules, IR for the cytoplasmic domain in A/D-cells was restricted to a juxtanuclear region, perhaps indicating its cleavage in Golgi areas. Although glucagon, insulin, and somatostatin are non-amidated, amidated peptides (glucagon-like peptide 1, adrenomedullin, proadrenomedullin N-terminal 20 peptide) were found in the three cell types.

The transmembrane domain enhances granular targeting of P-selectin

P-selectin is an integral membrane glycoprotein that is stored in granules of endothelial cells and platelets. The cytoplasmic domain of P-selectin is known to contain at least part of the signal that directs the protein to storage granules. In order to more fully understand how P-selectin is targeted to the regulated secretory pathway, we have expressed chimeric constructs between P- and E-selectin, a protein which is expressed on the cell surface, in a rat insulinoma cell line. Immunofluorescence studies indicated that replacing the cytoplasmic domain of E-selectin with that of P-selectin resulted in low-level granular expression. In contrast, when both the transmembrane and cytoplasmic domains of E-selectin were replaced with the analogous domains of P-selectin, the granular localization appeared greatly increased. This was confirmed by immunoelectron microscopy which demonstrated a three- to fourfold improvement in granular targeting, i.e. similar to wild-type P-selectin. The transmembrane domain had to be in the context of the P-selectin cytoplasmic domain as this membrane-spanning region could not induce granular targeting on its own. These results describe a novel function for the transmembrane domain of P-selectin in enhancing the efficiency of granular targeting and further implicate protein transmembrane domains in intracellular trafficking.

Expression in human lung cancer cell lines of genes of prohormone processing and the neuroendocrine phenotype

Lung tumor cells and cell lines, principally the histologically classified small cell lung cancer, are characterized by the expression of neuroendocrine (NE) features including AADC (aromatic amino acid decarboxylase, previously called DOPA decarboxylase) and the production of many peptide hormones. The general mechanisms by which most aspects of the NE phenotype affect the clinical behavior of lung tumor cells are unknown, but it is well recognized that peptide hormones can have systemic effects (paraneoplastic syndromes) and several have been shown to be autocrine growth factors for cancer cells. In order to determine the relationship between expression of different aspects of the NE phenotype in lung cancer cell lines, we have compared expression of a gene required for biosynthesis of some active peptide hormones (PAM, peptidylglycine alpha-amidating monooxygenase) to the gene for AADC in 32 lung cancer cell lines. Expression of these genes was quantified by both steady state Northern blot analysis and radiochemical enzymatic activity measurements. To ensure a range of expression of NE markers, non-small cell lung cancer (NSCLC) cell lines were chosen to include several which had previously been shown to express NE markers, and several small cell lung cancer (SCLC) cell lines with previous low levels of AADC were included. PAM enzyme activity and Northern blot analysis showed a two to three log variation in levels of expression in both the small cell and non-small cell lines. A smaller range was found for AADC expression. Using the highly sensitive PAM enzyme assays, all cell lines were found to express detectable PAM. PAM activities were secreted into the growth medium of all cell lines. There was no simple correlation apparent between AADC and PAM gene expression in the lung cancer cell lines. However, classic small cell lines demonstrated high levels of expression of both PAM and AADC genes, as did the carcinoid subset of the NSCLC lines. NSCLC lines expressed levels of PAM mRNA and enzyme activities equivalent to those of SCLC but had infrequent expression of AADC (principally only carcinoid NSCLC expressed AADC). These data demonstrate that separate aspects of the NE phenotype can be differentially expressed in lung cancer histological sub-types. Expression of PAM enzymes in all sub-types of lung cancer suggests that peptide prohormone activation may be a common mechanism for autocrine growth stimulation even in non-Ne NSCLC cell lines, or may reflect maintenance in cell lines of a common pathway of lung tumor promotion.

Human peptidylglycine alpha-amidating monooxygenase transcripts derived by alternative mRNA splicing of an unreported exon

We are characterizing the alternatively spliced human peptidylglycine alpha-amidating monooxygenase (hPAM)-encoding mRNA transcripts expressed by human cells. Reverse transcription coupled to the polymerase chain reaction (RT-PCR) has been used to identify four alternatively spliced variants that differ in the region joining the two catalytic domains. Two of the transcripts represent previously reported splice variants differentiated by the presence (hPAM-A) or absence (hPAM-B) of a 321-nucleotide (nt) linker (optional exon A) which in the rat produce functionally distinct enzymes. Different mRNAs represent two splice variants, hPAM-C and hPAM-D, that show the presence of an exon unreported for PAM in any other species. This new exon, designated exon C, is 54 nt in length, encodes an 18-amino-acid (aa) peptide containing a conserved dibasic aa endoproteolytic processing motif, and is located 3' of exon A in human genomic DNA. We propose that cell-specific regulation of mRNA splicing would provide a mechanism for control of prohormone activation by these variants of the PAM enzyme.

Comparison of chromogranin A and pancreastatin levels in plasma of patients with pancreatic islet cell tumor

The plasma levels of chromogranin A (CGA) in patients with islet cell tumor and plasma CGA responses to administration of a somatostatin analogue (Octreotide) in two of these patients were examined in comparison with plasma pancreastatin (PST) levels. There was a significant correlation between the fasting plasma levels of CGA and PST (r = 0.6, P < 0.001). Administration of the somatostatin analogue reduced the plasma concentrations of PST and CGA within 1 h, but the responses of CGA and PST to the analogue were not parallel in either patient. Thus, the suppressive effects of the analogue on the secretions of PST and CGA may be different. The results suggest the value of the PST and CGA assays used in this study.