PROGRESSION OF HORMONE-DEPENDENT ADENOCARCINOMA CELLS TO HORMONE-INDEPENDENT SPINDLE CARCINOMA-CELLS IN-VITRO IN A CLONAL SPONTANEOUS RAT MAMMARY-TUMOR CELL-LINE

A hormone-dependent, clonal carcinoma cell line, designated RM22-F5, w as derived from a malignant mammary mixed tumor spontaneously arising in an outbred old female Wistar rat. These cells expressed keratin and desmosomal protein and formed epithelial monolayers in a growth facto r and hormone-supplemented medium (LHC-8) containing 10% fetal bovine serum (E-type cells). Cells subcultured for 6 to 8 passages in RPMI 16 40 medium containing 10% fetal bovine serum without supplements appear ed to be fibroblastic and expressed vimentin (F-type cells). The shift to a fibroblast-like morphology was associated with a more malignant phenotype which included rapid, hormone-independent growth and invasiv e sarcoma-like character in nude mice. F-type cells were no longer abl e to express their original epithelial phenotype in LHC-8 medium. Cyto genetic analysis revealed that both E- and F-type cells had essentiall y the same karyotype. Analysis of PCR-amplified DNA further demonstrat ed a point mutation of the H-ras-1 gene at codon 12 and loss of the no rmal H-ras-1 allele in both cell types. Genetic tagging of E-type cell s with the neomycin-resistance gene resulted in the generation of F-ty pe cells with neomycin resistance in RPMI 1640 medium, suggesting that F-type cells are a malignant variant of E-type cells arising during i ra vitro culture, Somatic cell fusion between E- and F-type cells reve aled that with most hybrid clones tested, the fibroblast like phenotyp e was greatly suppressed, These results suggest that an irreversible p henotypic transition, representative of tumor progression from hormone -dependent adenocarcinoma to more malignant hormone independent spindl e carcinoma cells, is a recessive event and may involve loss of a supp ressor function.