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 li nes in vivo from primary thyroid tumors induced by N-bis-(2-hydroxypro pyl)nitrosamine (DHPN). In the present study, an insulin-like growth f actor I (IGF-I)-responsive cell line (TRTC-G1-C-A(4)) in culture was d erived from one (well differentiated papillary type) of these carcinom a cell lines G1, TRTC-G1-C-A(4) cells were found to exhibit specific s aturable binding of IGF-I with a K-d of 1.16 nM at approximately 43.6 fmol/10(5) cells. Inclusion of IGF-I (10 and 50 ng/ml) in the culture medium resulted in a significant increase of [H-3]thymidine incorporat ion and marked cell proliferation. IGF-II (10 ng/ml) and insulin (1 mu g) produced no such effects, The molecular weight of IGF-I receptors on the cell membrane was determined by Western blotting analysis, a si ngle band of binding proteins with a molecular weight of 125 kDa being evident under non-reducing conditions, Reverse transcriptase polymera se chain reaction (RT-PCR) showed that the TRTC-G1-C-A(4) cells contai ned IGF-I receptor mRNA with a sequence corresponding to that determin ed 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.