PROGESTERONE-RECEPTOR HETEROGENEITY IN MCF-7 CELL SUBCLONES IS RELATED TO CLONAL ORIGIN AND KINETICS DATA

Heterogeneity of progesterone receptor (PR) expression in MCF-7 cells is generally attributed to the coexistence of several sublines, each p ossessing different stages of differentiation. One hypothesis is that the variation of PR distribution relates to the genotype cell heritage and cell cycle phases. The aim of this study was to demonstrate the i mplication of cell subclones in PR heterogeneity. MCF-7 cell line subc lones were obtained initially by the limit dilution method on microsco pic slides, On these slides PR was assessed by immunofluorescence. 20 of the subclones were PR-negative, 10 were positive with varying degre es of PR expression. As these cell populations arose from a single cel l, they can be considered as monoclonal. These results show that PR he terogeneity (positive vs. negative clones) is based on a clonal origin and could be genotypically explained. In a second experiment four PR- positive MCF-7 cell subclones were maintained in continuous culture an d studied. On each one a triple fluorescent staining (PR, Ki-67 antige n and DNA) was performed and the reactions were quantified by videoflu oro microscopy. These results demonstrated that a relation between cel l PR content and cell cycle stages exists in these four subclones. Cel ls in G(0) express only little PR; PR level increases during the S pha se to reach a maximum in the G(2) phase; after mitosis PR level decrea ses with cell division and degradation may occur in G(1): PR level rea ches a minimum in late G(1) and in the early S phase. The doubling tim es of the different MCF-7 subclones shows that those that are rapidly cycling were preferentially PR-positive, whereas slowly cycling MCF-7 subclones were PR-negative. We conclude that in MCF-7 cells some subcl ones are able or not able to synthesize PR; PR content is directly dep endent on cell cycle phase and population doubling time.