Zebrafish IGFBP-2 inhibits cell growth and DNA synthesis. (A) Overexpression of zebrafish IGFBP-2 inhibits CHO cell growth. Growth curves of wild-type CHO cells (□), the pRC/CMV vector-transfected clone 1 (○) and clone 2 (▵), and the pRc/CMV-IGFBP-2-transfected clone 2 (●) and clone 6 (▴) are shown. *, P < 0.01 (n = 8) compared with the wild-type controls. (B) Effect of zebrafish IGFBP-2 on IGF-I-stimulated DNA synthesis in cultured zebrafish cells. Confluent cells were exposed to serum-free medium or IGF-I (100 ng/ml) in the presence of various concentrations of CM prepared from wild-type (open bars), mock-transfected (hatched bars), and zebrafish IGFBP-2-transfected cells (filled bars). The values are means ± SE of three separate experiments, each of which was performed in triplicate. *, P < 0.05 compared with the IGF-I alone group.