INSULIN-RECEPTOR AND INSULIN SENSITIVITY IN A CHICKEN HEPATOMA-CELL LINE

Insulin receptors have been characterized in a cell line recently isol ated from a chicken hepatoma (LMH). The binding of I-125-insulin to LM H cells or membranes displayed the expected criteria for insulin recep tors: affinity, temperature dependency, curvilinearity of Scatchard pl ot, rank order of potency for insulin analogs and insulin induced down -regulation. The a-subunit of LMH cell insulin receptors exhibited a n ormal size of 135 kDa. Following autophosphorylation, LMH WGA-purified receptors revealed a 95 kDa beta-subunit and a 72 kDa protein (pp72). Both proteins were phosphorylated in a time-, insulin- (and insulin-l ike growth factor 1, IGF-1) and manganese-dependent manner, and were p recipitated by antiphosphotyrosine and two anti-insulin receptor antib odies. The 72 kDa protein was not present under non-reducing condition PAGE or in normal chicken liver. These results strongly suggest that pp72 is either a truncated form of the insulin receptor beta-subunit s pecific to LMH cells or a degradation product. Lectin-purified insulin receptors from LMH cells or chicken liver membranes exhibited similar tyrosine kinase activity, using artificial substrate poly(Glu-Tyr) 4: 1. Finally, amino acid uptake by LMH cells was insulin stimulatable.