The overall objective of the project will be to apply the techniques of somatic cell genetics (cell hybridization, isolation and characterization of variant cell lines) to a study of the mechanism of action of insulin and insulin-like polypeptide hormones. The mouse melanoma cell line PG19 is unresponsive to the growth-stimulatory activity of insulin, and this cell line also lacks high affinity insulin receptors. Human diploid fibroblasts (which have insulin receptors, and receptors for the insulin-like polypeptide hormone MSA) and IM-9 lymphoblasts (which have only insulin receptors) will be hybridized with the PG19 melanoma cells. The resultant hybrid clones will be tested for their responsiveness to insulin and MSA. The parameters examined will include stimulation of transport, and induction of DNA systhesis. The hybrid clones will also be examined for the presence or absence of insulin and MSA receptors. It should be possible from these experiments to define the difference between the intracellular events that are stimulated by interaction of the two hormones with insulin receptor and with the MSA receptor. In addition, the same hybrid clones will be used to map the human genes for the insulin and MSA receptors. A search for variant cell lines that are unresponsive to the growth-stimulatory action of insulin and MSA will also be undertaken.