[The relationship between insulin-like growth factor-binding proteins and cell differentiation of osteoblastic clone MC3T3-E1 cells].
Insulin-like growth factors, which are important local factors in bone, are associated with specific binding proteins (IGFBPs). In this study, the relationship between IGFBPs and cell differentiation of MC3T3-E1 cells (E1 cells), a clonal osteoblast-like mouse calvarial cell line, was investigated. IGFBP-3 had no effect on alkaline phosphatase (ALP) activity of E1 cells, but in the presence of IGF-II at an ineffective concentration stimulated ALP activity. ALP activity of E1 cells cultured in alpha-MEM supplemented with 10% fetal calf serum (FCS) gradually increased after confluency, which demonstrated that E1 cells differentiate. In this experiment, 39 kd IGFBP-3 of FCS origin was decreased in the conditioned medium after 48 hours of culture of the cells obtained on day 0 after confluency, but not of those obtained on day 21, which suggests that the use of IGFBP-3 of FCS origin is diminished related with cell differentiation and E1 cells secrete themselves. E1 cells secreted three IGFBP, Mr 23, 26, and 31kd. Secretion of 31kd IGFBP gradually increased, and this increase correlated with ALP activity of E1 cells. These findings suggest that secretion of 31kd IGFBP is related with osteogenic differentiation of E1 cells.