Posttranscriptional regulation of α-casein mRNA accumulation by laminin

We have utilized primary cultures of rat mammary epithelial cells to study mechanisms by which laminin regulates the prolactin-dependent accumulation of α-casein mRNA. Mammary cells accumulate approximately fivefold more α-casein mRNA when cultured on laminin than when cultured on tissue plastic and the accumulation of α-casein mRNA is prolactin dependent. On the basis of transcription assays there is approximately a twofold increase in the α-casein mRNA transcription rate in cells cultured on laminin over that of tissue culture plastic. Measurements on the turnover of α-casein mRNA show that this mRNA is stabilized four-fold more on laminin than on tissue culture plastic, while there was no significant difference in the turnover of poly(A) RNA on either substratum. These data indicate that laminin regulates the cytoplasmic levels of α-casein mRNA accumulation primarily at the post-transcriptional level by increasing the stabilization of this mRNA.