Dependence of the structural MuMTV protein expression on hormone-induced murine mammary carcinoma GR/mt cell differentiation in vitro.

Effect of three hormones on the clonal cell line, originating from the stable GR/mt mammary carcinoma (MC) cell line was studied. In the hormones free media the cells had fibroblast-like shapes. Normal differentiation markers and MuMTV protein processing could not be revealed. Insulin favors epithelial cell shape and growth pattern induction, Thy 1.2 antigen expression, as it was shown by FIF test and increased clonogenicity in semisolid medium. Prolactin produces elongated, fusiform cells, milk protein synthesis and loss of clonogenicity. Both hormones exert no influence on the MuMTV protein precursors processing, as it was revealed in RIP test. Dexamethasone renders no visible influence on the cell differentiation except influence on the actin filament expression and intensification of the morphogenetic insulin action. Besides, dexamethasone switches on the env (but not the gag) product precursor processing, however, expression of the mature envelope protein on the cellular membranes occurred only in cells, entering the insulin-induced type of differentiation, as it was shown by RIP test with iodinated cells and MIF test. The gag precursor processing occurred only in extracellular virions. Delay of this process might be responsible for the preferential A-particle production by the cells described.