Differential regulation of insulin‐like growth factor binding protein (IGFBP)‐2 mRNA in liver and bone cells by insulin and retinoic acid in vitro

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Abstract
Isolated cells produce insulin‐like growth factors (IGFs) and their binding proteins (IGFBPs). Two distinct cell types were studied with regard to IGFBP‐2 expression: (i) rat hepatocytes, which produce IGF I at a high rate and thus regulate its plasma concentration; and (ii) rat osteoblasts, which are targets of IGF I action. IGFBP‐2 expression is low in hepatocytes prepared from normal adult rats and high in calvaria cells from newborn rats. Retinoic acid stimulates IGFBP‐2 production by liver cells. Insulin suppresses both basal and retinoic acid‐induced IGFBP‐2 mRNA expression in hepatocytes and has no such effect on osteoblasts. Retinoic acid and insulin regulate IGFBP‐2 expression in a tissue‐specific manner.