Growth and differentiation of hyperplastic outgrowths derived from mouse mammary epithelial cells transformed in organ culture.

Potentially neoplastic outgrowths of BALB/c mouse mammary hyperplasia(s) (MH) derived from 7,12-dimethylbenz[a]anthracene-transformed epithelial cells in organ culture were characterized for responses to the hormones normally required for morphogenesis and functional differentiation of the mammary tissue. In a new culture model of the gland-free mammary fat pad, DNA synthesis in the MH outgrowths increased to a single peak during 6 days of incubation in a serum-free medium containing insulin, prolactin, aldosterone, and cortisol. The rise in DNA synthesis was accompanied by increased cell number and lobuloalveolar morphogenesis filling 50-70% of the fat pad; the rate of growth was variable among the MH outgrowth lines. Certain MH tissue showed some growth response in medium with aldosterone, cortisol, or estrogen, and progesterone in the presence of insulin. The hormone mixture insulin-prolactin was conducive to maximal growth, which suggested an altered sensitivity of the MH outgrowths to the mammogenic steroid hormones. Functional differentiation in the MH outgrowths was assessed in vivo by determination of the casein messenger RNA (mRNAcsn) levels measured by a specific complementary DNA probe. In MH-1 and MH-5 outgrowth lines, mRNAcsn was measurable in lactating hosts. In MH-9 outgrowth essentially the same concentration of mRNAcsn was present both in virgin and lactating hosts. Although mRNAcsn was present in MH outgrowths in lactating hosts, the concentration of the mRNA was only 0.056-0.88% of that present in the lactating host's own mammary gland. Virtually no mRNAcsn was measurable in the mammary tumors, regardless of the endocrine environment of the host animal. The results indicate a transformation-associated altered pattern of mammary cell-specific gene expression.