Developmental regulation of murine mammary-gland 90 kDa heat-shock proteins.

We have examined the regulation of murine mammary-gland 90 kDa heat-shock protein (hsp-90) as a function of normal development and differentiation. We find that both hsp-90 and amounts of its mRNA are modulated during development and differentiation, with the highest concentrations of mRNA and protein being present in tissues from pregnant and lactating animals respectively. Metabolic labelling experiments with [35S]methionine reveal that the rate of synthesis of hsp-90 also varies among tissues from various developmental states and correlates with the relative hsp-90 mRNA content. These data also suggest that the highest concentration of hsp-90 found in lactating mammary tissues may be due to a greater stability of this protein in this developmental state. The possible significance of the developmental modulation of mammary hsp-90 to mammary steroid-receptor properties is discussed.