TGFβ suppresses casein synthesis in mouse mammary explants and may play a role in controlling milk levels during pregnancy

Abstract

Mammary explants from 14-15-d-pregnant mice synthesize and secrete milk proteins in culture in response to insulin, hydrocortisone, and prolactin. Here we demonstrate that transforming growth factor β (TGFβ) treatment suppresses, in a dose dependent and reversible manner, the ability of explants to synthesize and secrete milk caseins. TGFβ does not affect the level of casein mRNA within explants but inhibits casein synthesis posttranscriptionally. We also show increased expression of TGFβ2 and TGFβ3 in intact mammary gland as pregnancy progresses, with reduced expression of all three TGFβs at the onset of lactation. These findings suggest that endogenously produced TGFβ may limit the accumulation of milk caseins that are produced in the mammary gland during pregnancy.