DISCORDANT REGULATION OF INSULIN-LIKE GROWTH FACTOR-II AND INSULIN-LIKE GROWTH-FACTOR BINDING PROTEIN-2 GENE-EXPRESSION IN A RAT BETA-CELL LINE

Expression and regulation of IGFBP-2 and IGF-II by GH and glucose in t he rat insulin producing beta-cell line, INS-I, were determined. These cells express high levels of the insulin-like growth factor II (IGF-I I) gene which is regulated by glucose, GH has no regulatory activities on IGF-II or IGFBP-2 gene expression. The levels of IGF-II and IGFBP- 2 mRNA at increasing glucose concentrations are inversely regulated an d exogenously added insulin inhibits IGFBP-2 gene expression at low gl ucose. These observations suggest that the expression of IGFBP-2 gene in this cell line is under the negative control of the endogenously pr oduced insulin (and/or IGF-II) which accumulates to effective levels i n the medium when the cells are cultured at high glucose concentration s.