Abstract
The present study was designed to assess the effectiveness of multiplication-stimulating activity (MSA), an insulin-like growth factor, in supporting the growth of F9 cells (an embryonal carcinoma line with properties similar to embryonic stem cells). Under serum-free growth conditions in a medium supplemented with transferrin and fibronectin, MSA is an effective mitogen. At 100 ng/ml, MSA completely replaces the growth requirement for fetal calf serum. Biologically active MSA polypeptides II and III act as potent growth promoters of F9 cells, whereas MSA I appears to be somewhat less effective. Binding studies carried out with [125I]iodo-MSA indicate that F9 cells possess specific receptors for MSA. Scatchard analysis indicates a single class of MSA receptors with a Ka of 8.2 x 10(9) M-1; about 55,000 MSA molecules can bind per F9 cell. Insulin-like growth factor I and II both complete for MSA binding, whereas insulin does not compete. Since insulin is an effective promoter of F9 cell growth, these results indicate that the mitogenic action of insulin toward F9 cells is not mediated through MSA receptors. It is apparent from these results that MSA is capable of serving as an early embryonic growth factor.
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