Biochemical analysis of secretory proteins synthesized by normal rat pancreas and by pancreatic acinar tumor cells.

Abstract

We have examined the secretogogue responsiveness and the pattern of secretory proteins produced by a transplantable rat pancreatic acinar cell tumor. Dispersed tumor cells were found to discharge secretory proteins in vitro when incubated with hormones that act on four different classes of receptors: carbamylcholine, caerulein, secretin-vasoactive intestinal peptide, and bombesin. With all hormones tested, maximal discharge from tumor cells was only about one-half that of control pancreatic Iobules, but occurred at the same dose optima except for secretin, whose dose optimum was 10-fold higher. Biochemical analysis of secretory proteins discharged by the tumor cells was carried out by crossed immunoelectrophoresis and by two-dimensional isoelectric focusing-SDS polyacrylamide gel electrophoresis. To establish a baseline for comparison, secretory proteins from normal rat pancreas were identified according to enzymatic activity and correlated with migration position on two-dimensional gels.Our results indicate that a group of basic polypeptides including proelastase, basic trypsinogen, basic chymotrypsinogen, and ribonuclease, two out of three forms of procarboxypeptidase B, and the major lipase species were greatly reduced or absent in tumor cell secretion. In contrast, the amount of acidic chymotrypsinogen was notably increased compared with normal acinar cells. Although the acinar tumor cells are highly differentiated cytologically and express functional receptors for several classes of pancreatic secretagogues, they show quantitative and qualitative differences when compared with normal pancreas with regard to their production of secretory proteins.The acinar cell of the mammalian pancreas is highly differentiated and adapted for the synthesis, packaging, and discharge of secretory proteins. The anatomic organization of organdies within the cell expedites the secretory process in that the protein synthetic apparatus is located in the basal pole of the cell while secretory granules accumulate in the apical pole. Under physiologic conditions, hormones interact with receptors located on the basal plasmalemma, which in turn leads to granule release at the apical membrane. Specialized regions of the plasma membrane may play a role in directing vectorial release of secretory proteins. Evidence for such specialization includes differences in intramembrane particle distribution between basolateral and apical membranes as shown by freezefracture electron microscopy (1) as well as by marked differences in distribution of lectin binding sites (2). As we have shown in previous papers (3, 4), rat pancreatic acinar tumor cells lack polarized organization of the plasmalemma as deter-734 mined by either freeze-fracture techniques or lectin binding. Though the acinar tumor ceils contain the cellular machinery for the production and packaging of secretory proteins, it is not known whether the lack of polar organization of the plasmalemma compromises their response to peptide secretagogues.In this investigation we sough...

Characterisation of the progression of azaserine-induced rat pancreatic adenocarcinoma by proliferative cell nuclear antigen, basement membrane laminin and trypsinogen immunohistochemistry

“…And finally, our finding that BML was not expressed in invasive carcinomas is in agreement with the results of studies on several types of tumours (Barsky et al 1983;Bosman 1994). Most human acinar cell carcinomas of the pancreas were immunohistochemically positive for TG or trypsin (Morohoshi et al 1987;Klimstra et al 1992;Samuel and Frierson 1996;Labate et al 1997), and transplantable rat pancreatic acinar cell tumours also contained TG (Longnecker et al 1979;Rao et al 1980;Iwanij and Jamieson 1982), but in these studies different progressional stages including invasive AC could not be distinguished. Our special stage, the month 13 adenoma is an exception among the premalignant stages hitherto investigated, but the positive correlation between the elevated BML level, increased cellular proliferation and even microvessel density (Nagy et al unpublished result) unquestionably indicates the existence of a premalignant growth stage between months 10 and 15.…”

Comparison of secretory protein and membrane composition of secretory granules isolated from normal and neoplastic pancreatic acinar cells of rats.

“…The remaining cells represent a spectrum of cytodifferentiation and contain a few or no wellformed zymogen granules (6,22 (1,27). The marked reduction of this glycoprotein in tumor secretory granule membranes may account in part for the diminished secretory response to hormonal stimuli (23,29). The function of the other absent or reduced polypeptides in the tumor membrane is also unclear.…”

“…4). Enzyme activities and the available molecular weight information about rat and guinea pig pancreatic exocrine secretory proteins (1,11,23,24) allowed specific identification of various spots in the two-dimensional gels ( Table 1). The nature of spot p24 remains to be determined.…”

L-Azaserine Induced Preneoplasia in the Rat Pancreas. A Morphometric Study of Dietary Manipulation (Lipotrope Deficiency) and Ultrastructural Differentiation

“…By accepting the view that there are decreased, rather than increased, amounts of zymogen in AACF cells, we argue that AACL are not "zymogen rich." It is hypothesized that these lesions "de-differentiate" and become lacking in zymogen as has been reported in acinar cell tumors (6,7,11). The eosinophilia of the AACL is likely to be due to the increased concentration of cells in a given section area and the increased numbers of granules in the cells, and not to increased amounts of zymogen.…”

“…Pancreatic acinar tumor cells in culture have been demonstrated to discharge 50% less zymogen per lobule than normal cells (6,7). Adducts on the DNA may very well alter messages that govern packaging and transport of zymogen granules; or formation of plasmalemmal receptors that receive hormonal stimulation leading to release of zymogen.…”