A human breast epithelial cell type with stem cell characteristics as target cells for carcinogenesis

Two types of human breast epithelial cells (HBEC) have been characterized. In contrast to Type II HBEC, which express basal epithelial cell phenotypes , Type I HBEC are deficient in gap junctional intercellular communication a nd are capable of anchorage-independent growth and of expressing luminal ep ithelial cell markers, estrogen receptors, and stem cell characteristics (i .e. the ability to differentiate into other cell types and to form budding/ ductal organoids on Matrigel). A comparative study of these two types of ce lls has revealed a high susceptibility of Type I HBEC to immortalization by SV40 large T antigen, although both types of cells are equally capable of acquiring an extended life span (bypassing senescence) after transfection w ith SV40. The immortalization was accompanied by elevation of a low level o f telomerase activity in the parental cells after mid-passage (similar to 6 0 cumulative population doubling levels). Thus HBEC do have a low level of telomerase activity, and Type I HBEC with stem cell characteristics are mor e susceptible to telomerase activation and immortalization, a mechanism whi ch might qualify them as target cells for breast carcinogenesis. The immort alized Type I HBEC can be converted to highly tumorigenic cells by further treatment with X rays (2 Gy x 2) and transfection with a mutated ERBB2 (als o known as NEU) oncogene, resulting in the expression of p185(ERBB2) which is tyrosine phosphorylated, (C) 2001 by Radiation Research Society.