We have previously established that secretory
proteins from a rat acinar cell
tumor lack two forms of
procarboxypeptidase B, are deficient in a major
lipase species, and possess markedly reduced amounts of the basic
proteins proelastase, basic
chymotrypsinogen, basic
trypsinogen and
ribonuclease (Iwanij, V., and J.D. Jamieson, J. Cell Biol., 95:734-741). Because secretory
proteins are markers for acinar cell differentiation, we sought to establish whether the secretory
protein profile of the acinar cell
tumor is unique to the transformed cell or whether it resembles that of a stage of normal pancreatic development. To this end, we compared the secretory
protein pattern from acinar
tumor cells with that of rat pancreatic rudiments at days 19-22 of gestation and through day 21 of the postnatal period. Two-dimensional IEF-SDS gel electrophoresis coupled with biosynthetic labeling and fluorography indicates a time-dependent appearance of individual secretory
proteins with basic
polypeptides, except for
amylase, appearing in the terminal stages of differentiation. In comparison, the secretory
protein pattern of the acinar
tumor cells most closely resembles that of day-19 embryonic pancreatic rudiments. We propose that the cells of the acinar cell
tumor may, in part, mirror a stage of normal pancreatic development.