INSULIN-LIKE GROWTH-FACTOR-I (IGF-1) SPECIFICALLY BINDS TO BOVINE LENS EPITHELIAL-CELLS AND INCREASES THE NUMBER OF FIBRONECTIN RECEPTOR-SITES

The purpose of the study was to determine the quantitative characteris tics of IGF-1 binding sites in lens cells and to investigate its abili ty to modulate cell growth, in particular by inducing integrin express ion. Studies were carried out in bovine lens epithelial cells in cultu re. IGF-1 receptor binding parameters were measured from saturation ex periments with I-125-IGF-1. Scatchard plot indicates one class of high affinity sites (Kd = 2.5 +/- 1.5 nM). In addition, we showed that thi s growth factor was synthesized and released by lens cells. The charac teristics of the receptor sites are in accordance with the effects of the growth factor (e.g. stimulation of DNA synthesis) in the range of nM concentrations. Moreover, by incubating cells with IGF-1 (12 nM) fo r 40 hr we demonstrated that the expression of integrin, the fibronect in receptor, was activated (N = 885 +/- 169 x 10(3) sites/cell vs N = 453 +/- 105 x 10(3) sites/cell in control cultures) without modificati on of its affinity (Kd = 16 x 10(-8) M). These new data emphasize the role of IGF-1 in the regulation of migration, proliferation and differ entiation of mature lens cells.