Presence of CCK-B Receptor mRNA in Human Functionless Pituitary Tumors

摘要

Cholecystokinin (CCK) is a peptide found widely distributed throughout the gut and nervous systems. There is growing evidence that it affects growth and differentiation of several types of cell, including anterior pituitary cells, via two receptor subtypes, A and B. An autocrine/paracrine role for CCK in GH3 rat pituitary tumor cells has been reported. Herein, we demonstrate that functionless human pituitary tumors also possess CCK-B receptors. Total RNA was extracted from 30 human functionless pituitary tumors, reverse transcribed into cDNA, and subjected to PCR using primers specific for CCK-A and CCK-B receptors. The primers were targeted against different exons of the receptor genes, allowing identification of cDNA amplification. PCR bands of the predicted length were observed in all tumors using CCK-B receptor primers. Restriction digestion and direct sequence analysis of the products provided further evidence that they represented CCK-B receptor mRNA. CCK-A receptor mRNA was not detected by this RT-PCR analysis. In culture, CCK and CCK octapeptide sulphate powerfully stimulated phosphatidylinositol hydrolysis, providing evidence for functional activity of the CCK-B receptors. Similar analyses on pituitary-derived fibroblasts yielded negative results, indicating that the CCK-B receptor mRNA was expressed by tumors cells. These results suggest a role for CCK in the development of human functionless pituitary tumors.