Rat pancreatic stone protein messenger RNA. Abundant expression in mature exocrine cells, regulation by food content, and sequence identity with the endocrine reg transcript.

We used a cDNA encoding the human pancreatic stone protein (PSP-S), the secretory inhibitor of CaCO3 crystal growth, as a probe for cloning rat PSP-S messenger RNA. Overlapping clones gave a mRNA sequence of 783 nucleotides encoding a preprotein of 165 amino acids including a prepeptide of 21 amino acids. Rat and human PSP-S showed 70% identity, and the mature proteins had the same length. PSP-S mRNA concentration was measured in the pancreas of rats adapted to diets containing 15, 25, or 70% protein. Compared with the 15% protein diet, concentration increased 3 and 12 times with the diets with 25 and 70% protein, respectively, which is 3 times higher than for serine proteases. A complete sequence identity was observed between the rat PSP-S transcript and the reg mRNA described by Terazono et al. (Terazono, K., Yamamoto, H., Takasawa, S., Shiga, K., Yonemura, Y., Tochino, Y., and Okamoto, H. (1988) J. Biol. Chem. 263, 2111-2114), which is expressed in regenerating pancreatic islets but not in mature islets. A specific role of the reg protein in islet regeneration was suggested. We found that PSP-S (reg) mRNA concentration was indeed increased in isolated regenerating islets. Yet, a transient increase was also observed in exocrine tissue during the initial phase of regeneration following pancreatectomy or acute pancreatitis, suggesting increased expression during cell dedifferentiation. It is concluded that, in mature pancreas, expression of the reg/PSP-S gene occurs primarily in acinar cells. The gene product, which encodes a secretory protein inhibiting CaCO3 crystal growth in juice, is unlikely to play a specific role in islet regeneration.