STUDIES ON THE CELL-CYCLE DEPENDENCY OF THE ACTIONS OF INSULIN-LIKE GROWTH FACTOR-I IN BALB/C 3T3 CELLS

The present study was conducted to determine the cell‐cycle dependency of various actions of IGF‐I in Balb/c 3T3 cells. When autophosphorylation of the IGF‐I receptor was determined in [32P]‐labelled cells, IGF‐I increased radioactivity in a 100 K‐Da phosphoprotein, presumably β‐subunit of the IGF‐I receptor, both in quiesent and in primed competent cells. Likewise, IGF‐I stimulated uptake of [3H]deoxyglucose independent of the cell cycle. In contrast, IGF‐I increased calcium entry, radioactivity in [3H]diacylglycerol, and [3H]thymidine incorporation in primed competent cells while these reactions were not induced by IGF‐I in quiescent cells. The latter three reactions were attenuated when cells were pretreated with pertussis toxin. These results indicate that some, but not all, of the actions of IGF‐I are dependent on the cell cycle in Balb/c 3T3 cells. They also suggest that a pertussis‐toxin‐sensitive G protein may be involved in the cellcycle‐dependent actions of IGF‐I. Copyright © 1990 Wiley‐Liss, Inc.