EXPRESSION AND REGULATION OF GROWTH-HORMONE (GH) AND PROLACTIN (PRL) RECEPTORS IN A RAT INSULIN-PRODUCING CELL-LINE (INS-1)

We have examined the expression of growth hormone (GH) and prolactin ( PRL) receptors, and the binding parameters of human GH (hGH), on the r at insulin producing cell line INS-1. We found that, like normal insul in producing beta-cells, INS-1 cells express both GH and PRL receptors , and the majority of human GH (hGH) binding sites on this cell line a re of lactogenic specificity. As calculated from Scatchard plots, abou t 6600 hGH binding sites with a K-a of 6.2 x 10(8) M(-1) are present p er cell. Northern blot analysis showed two mRNA species of 4 and 1.6 k b for the GH receptor and, one major species of 10.5 kb for the PRL re ceptor. The PRL receptor mRNA was up-regulated by bovine GH (bGH), rat PRL (rPRL), in a time- and dose-dependent manner. On the contrary, bG H and rPRL, down-regulated the expression of GH receptor gene. The imp ortance of this differential regulation in in vivo and in vitro studie s are discussed.