How cells grow, the discovery of Insulin like growth factors
In 1957, W.D. Salmon Jr and William H. Daughaday at Washington University in St Louis provided compelling evidence that the effects of growth hormone in stimulating the incorporation of radioactive sulfate into chondroitin sulfate in cartilagein vivoand in vitrowas not direct, but mediated by a factor circulating in serum that they named “sulfation factor” (5). In the early 70’s, many investigators started to search for the factor(s) mediating growth hormone effects that by consensus became known as “somatomedins” (6). Different groups used different target cell systems and different isolation and purification methods, resulting in a multiplicity of somatomedins of which the similarities and differences were unclear.
Somatomedin A was identified as a factor that promotes labelled sulfate uptake by chicken cartilage (7). Somatomedin B was identified as a factor that stimulates DNA synthesis in human glial cells (8,9). Future Nobel laureate Rosalyn Yalow developed in 1975 a radioimmunoassay for somatomedin B (10). Somatomedin C was a more basic peptide than somatomedin A or B and stimulated uptake of labelled sulfate into rat cartilage (11).
At about the same time, future Nobel laureate Howard Temin and coworkers isolated a new growth factor, which they named Multiplication Stimulation Activity (MSA), from serum-free medium that had been conditioned by a Buffalo rat liver cell line (BRL-3A) (12).
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