Characterization of an In Vitro Human Breast Epithelial Organoid System

Abstract

Abstract : The objectives of this study are 1) to identify factors that regulate the growth and differentiation of organoids formed by two types of normal human breast epithelial cells (HBEC) in Matrigel; 2) to characterize the expression and function of estrogen receptors (ER) in normal and in vitro neoplastically transformed HBEC; and 3) to determine if a HBEC type with stem cell characteristics (Type I) is more susceptible to telomerase activation and immortalization. The major results are 1) Type I HBEC in conjunction with Type II cells are capable of forming ductal and end bud or lobule 1-like structures in Matrigel which preserve the undifferentiated state of HBEC for a long time, evidence that Type I HBEC are stem cells; 2) Type I normal HBEC and their neoplastically transformed clones express a variant ER in vitro on plastic while expressing a wild type ER in tumors developed in nude mice or grown in vitro in Matrigel; 3) high susceptibility of Type I HBEC to telomerase activation and immortalization; and 4) the lifespan of HBEC can be effectively extended by co-transfection with a dominant-negative mutant p53 and the human c-myc. These findings indicate Type I stem cells as targets for carcinogenesis and inactivation of p53 and activation of telomerase as major events in initial stage of breast carcinogenesis.