Effects of androgens on subpopulations of the human osteosarcoma cell line SaOS2.

Previously, we showed that androgens stimulate murine and human osteoblast-like cell proliferation and differentiation by mechanisms involving increased responses to mitogenic growth factors (GF) and increased GF production. To explain this dual action of androgens on primary osteoblastic cell populations we advanced the hypothesis that androgens exert differential effects on osteoblastic subpopulations. We subcloned a human osteosarcoma cell line (SaOS2) into subpopulations expressing high (HAS) and low (LAS) levels of alkaline phosphatase (ALP). The obtained subclones differed significantly in their ALP production and expressed a high and low ALP phenotype, respectively, for the entire experimental period. Dihydrotestosterone (DHT) increased specific ALP activity and type-I procollagen peptide secretion in both HAS and LAS. DHT pretreatment enhanced the mitogenic action of basic fibroblast growth factor (bFGF) and insulinlike growth factor 2 (IGF2) only in HAS. The enhanced mitogenic effect of IGF2 in HAS after DHT pretreatment was associated with increased IGF2-receptor mRNA levels. Therefore, we conclude that androgens exert their osteoanabolic action (1) by stimulating differentiated functions of osteoblastic cells with a high and a low ALP phenotype, and (2) via increased growth factor receptor expression and thereby enhancing mitogenic growth factor responses only in HAS.