Hormonal regulation of tumor suppressor proteins in breast cancer cells

This laboratory is studying hormonal regulation of tumor suppressor protein s, p53 and retinoblastoma (pRB). Estrogen receptor and progesterone recepto r positive human breast cancer cell lines, T47D and MCF-7, were utilized fo r determining influence of hormonal and antihormonal agents on the level of expression of p53, state of phosphorylation of pRB, and rate of cell proli feration. The expression of p53 in T47D cells grown for 4-5 days in culture medium containing charcoal-treated (stripped) fetal bovine serum declined gradually to 10% of the level seen in control (whole serum, non charcoal-tr eated) groups. Supplementation of culture medium containing stripped serum with 0.1-1 nM estradiol (E-2) restored p53 to its level seen in the control within 6-24 h. Under above conditions, treatment of cells with R5020 or RU 486 reduced (15-30%) the level of p53. Incubation of cells in E-2-containin g growth medium caused cell proliferation and hyperphosphorylation of pRB; the latter effect was seen maximally between 24-72 h. The E-2-induced hyper phosphorylation of pRB and increase in the level of p53 were sensitive to t he presence of ICI and 4-hydroxy tamoxifen (OHT). T47D and MCF-7 cells were also transiently transfected with a P1CAT reporter plasmid containing c-My c responsive element and the levels of chloramphenicol acetyltransferase (C AT) activity were observed in response to various treatments. E-2 and OHT c aused P1CAT induction as seen by increased CAT activity: E-2 caused an endo genous increase in the expression of an ICI-sensitive c-Myc form. These dat a suggest that estrogen upregulates p53 expression while progesterone downr egulates this process. Further, E-2 regulates p53 level and pRB activity in a coordinated manner. (C) 2001 Elsevier Science Ltd. All rights reserved.