EGF-dependent growth inhibition in MDA-468 human breast cancer cells is characterized by late G 1 arrest and altered gene expression

Abstract

The MDA-468 human breast cancer cell line displays the unusual phenomenon of growth inhibition in response to pharmacological concentrations of EGF. This study was initiated with the objective of elucidating the cellular mechanisms involved in EGF-induced growth inhibition. Following EGF treatment the percentage of MDA-468 cells in G 1 phase increased, together with a concomitant depletion in S and G 2/M phase populations, as revealed by flow cytometry of DNA content. The apparent G 1 block in the cell cycle was confirmed by treating the cells with vinblastine. DNA synthesis was reduced to about 35% of that measured in control, untreated cells after 48 h of EGF treatment, as measured by the incorporation of [ 3H]thymidine. DNA synthesis returned to normal following the removal of EGF from the growth-arrested cells. In order to locate the EGF-induced event responsible for the G 1 arrest more precisely, we examined the expression of certain cell cycle-dependent genes by Northern blot analysis. EGF treatment did not alter either the induction of the early G 1 marker, c- myc, or the expression of the late G 1 markers, proliferating cell nuclear antigen, and thymidine kinase. However, EGF-treated cells revealed down regulation of p53 and histone 3.2 expression, which are expressed at the G 1/S boundary and in S phase, respectively. These results indicte that EGF-induced growth inhibition in MDA-468 human breast cancer cells is characterized by a reversible cell cycle block at the G 1/S boundary.