Expression and regulation of the insulin-like growth factor-1 receptor by growing and quiescent H4IIE hepatoma.
Recent evidence that insulin-like growth factor-1 (IGF-1) influences certain properties of H4IIE hepatoma cells independent of insulin led us to examine whether H4IIE cells express IGF-1 receptors. Competitive binding experiments demonstrated IGF-1, but not insulin or IGF-II, could compete with [125I]IGF-1. Chemical crosslinking detected a protein with an apparent mass of 175 kDa and its identity as the IGF-1 receptor alpha-subunit was confirmed by Western blotting. The apparent molecular mass of this protein decreased to 135 kDa following deglycosylation. Immunofluorescence microscopy verified that both insulin and IGF-1 receptors were present, although measurement of IGF-1 receptor quantity revealed they were less abundant than insulin receptors. Binding of IGF-1 was low in growing cells and higher in a quiescent cell population. Scatchard analysis confirmed that receptor density was increased in non-growing H4IIE cells while there was no apparent difference in receptor affinity. Western blot analysis and RT-PCR revealed that both protein and mRNA levels were elevated as cell growth ceased. Interestingly, addition of insulin to quiescent H4IIE cells, which stimulates cell proliferation, further increased IGF-1 receptor protein levels with a peak at 12-24 h. Distinct modes of regulating IGF-1 receptor expression are indicated.
Zahradka
P
P
Institute of Cardiovascular Sciences, St. Boniface General Hospital Research Centre, 351 Tache Avenue, Winnipeg, Man. R2H ZA6, Canada. peterz@sbrc.umanitoba.ca
Werner
J
J
Yau
L
L
D000818:Animals; D002455:Cell Division; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects*; D007004:Hypoglycemic Agents / Q000494:pharmacology*; D007328:Insulin / Q000494:pharmacology*; D007334:Insulin-Like Growth Factor I / Q000494:pharmacology*; D008114:Liver Neoplasms, Experimental / Q000378:metabolism* / Q000473:pathology*; D051381:Rats; D017526:Receptor, IGF Type 1 / Q000819:agonists / Q000096:biosynthesis* / Q000235:genetics; D014407:Tumor Cells, Cultured
D007004:Hypoglycemic Agents; D007328:Insulin; D007334:Insulin-Like Growth Factor I; D017526:Receptor, IGF Type 1