Abstract
MULTIPLICATION-STIMULATING activity (MSA), which is the name given to a family of polypeptides isolated from calf serum1 and from medium conditioned by certain rat liver cell cultures2, stimulates cellular DNA synthesis and growth, and has insulin-like activity. MSA is acid soluble, heat stable and has a molecular weight of approximately 10,0001,2. It shares these physical and biological properties with somatomedin3 and acid–ethanol soluble non-suppressible insulin-like activity (NSILA-s)4—polypeptides in human serum which may be important in human growth. We have now studied the interaction of MSA and insulin with chick embryo fibroblasts (CEF). We describe here the binding of labelled MSA to CEF, and correlate this binding with the stimulation of incorporation of 3H-thymidine into DNA. We propose that MSA and insulin stimulate DNA synthesis in CEF by interacting with a common growth receptor.
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