EXPRESSION AND REGULATION OF THE INSULIN-LIKE GROWTH-FACTOR-I RECEPTOR BY GROWING AND QUIESCENT H4IIE HEPATOMA

Recent evidence that insulin-like growth factor-1 (IGF-1) influences c ertain properties of H4IIE hepatoma cells independent of insulin led u s to examine whether H4IIE cells express IGF-1 receptors. Competitive binding experiments demonstrated IGF-1, but not insulin or IGF-II, cou ld compete with [I-125]IGF-1. Chemical crosslinking detected a protein with an apparent mass of 175 kDa and its identity as the IGF-1 recept or alpha-subunit was confirmed by Western blotting. The apparent molec ular mass of this protein decreased to 135 kDa following deglycosylati on. Immunofluorescence microscopy verified that both insulin and IGF-1 receptors were present, although measurement of IGF-1 receptor quanti ty revealed they were less abundant than insulin receptors. Binding of IGF-1 was low in growing cells and higher in a quiescent cell populat ion. Scatchard analysis confirmed that receptor density was increased in non-growing H4IIE cells while there was no apparent difference in r eceptor affinity. Western blot analysis and RT-PCR revealed that both protein and mRNA levels were elevated as cell growth ceased. Interesti ngly, addition of insulin to quiescent H4IIE cells, which stimulates c ell proliferation, further increased IGF-1 receptor protein levels wit h a peak at 12-24 h. Distinct modes of regulating IGF-1 receptor expre ssion are indicated. (C) 1998 Elsevier Science B.V. All rights reserve d.