Establishment of a rat thyroid carcinoma cell line in vitro demonstrating high DNA synthesis in response to insulin-like growth factor I

We previously established transplantable rat thyroid carcinoma cell lines in vivo from primary thyroid tumors induced by N-bis-(2-hydroxypropyl)nitrosamine (DHPN). In the present study, an insulin-like growth factor I (IGF-I)-responsive cell line (TRTC-G1-C-A4) in culture was derived from one (well differentiated papillary type) of these carcinoma cell lines G1. TRTC-G1-C-A4 cells were found to exhibit specific saturable binding of IGF-I with a Kd of 1.16 nM at approximately 43.6 fmol/105 cells. Inclusion of IGF-I (10 and 50 ng/ml) in the culture medium resulted in a significant increase of [3H]thymidine incorporation and marked cell proliferation. IGF-II (10 ng/ml) and insulin (1 μg) produced no such effects. The molecular weight of IGF-I receptors on the cell membrane was determined by Western blotting analysis, a single band of binding proteins with a molecular weight of 125 kDa being evident under non-reducing conditions. Reverse transcriptase polymerase chain reaction (RT-PCR) showed that the TRTC-G1-C-A4 cells contained IGF-I receptor mRNA with a sequence corresponding to that determined from rat uterus. These results demonstrate that the IGF-I receptor can be expressed in a thyroid carcinoma with an important contribution to cell growth.