Cholecystokinin receptor characterization and cholecystokinin-A receptor messenger RNA expression in transgenic mouse pancreatic carcinomas and dysplastic pancreas

Abstract

Transgenic mice bearing the rat elastase I promoter - SV40 T-antigen (ELSV) fusion gene develop pancreatic acinar cell carcinomas by 3-6 months of age. In other animal models of pancreatic cancer, cholecystokinin (CCK) has been shown to be a tumor promoter. Therefore, we characterized CCK binding properties and CCK-A receptor mRNA expression in pancreatic carcinomas and dysplastic pancreata from the Tg(Ela-1, SV40E+Ela-1, neo)Bri19 strain of ELSV transgenic mice. To accomplish this, we utilized 125I-Bolton-Hunter-labeled-cholecystokinin octapeptide (125I-BH-CCK-8) binding studies, reverse transcription-polymerase chain reaction (RT-PCR), and Southern blot analysis to examine pancreatic carcinomas from 26-week-old male ELSV transgenic mice, dysplastic pancreata from 8-week-old male ELSV transgenic mice, and normal pancreas from 30-week-old nontransgenic male mice (SJL/J) and 8-week-old nontransgenic male mice (B6SJLF1/J). Optimal saturable CCK-8 binding was detected at pH 6.5, 22 degrees C. Competitive inhibition 125I-BH-CCK-8 binding assays performed on all four mouse pancreatic tissues showed that CCK-8 bound to two classes of CCK binding sites: a high affinity, lower capacity CCK binding site and a low affinity, higher capacity CCK binding site. RT-PCR and Southern blot analysis confirmed the 125I-BH-CCK-8 binding studies by demonstrating CCK-A receptor mRNA expression in the ELSV transgenic pancreatic carcinomas and dysplastic pancreas, as well as in normal nontransgenic mouse pancreas. In conclusion, pancreatic carcinomas and dysplastic pancreas from ELSV transgenic mice and normal nontransgenic mouse pancreas all bind 125I-BH-CCK-8 and express mRNA for the CCK-A receptor. In contrast to chemically-induced pancreatic tumors in the rat, ELSV transgenic mouse pancreatic tumors do not appear to significantly overexpress CCK-A receptors.