Suppression of p53 function in normal human mammary epithelial cells increases sensitivity to extracellular matrix-induced apoptosis

Little is known about the fate of normal human mammary epithelial cells (HM ECs) that lose p53 function in the context of extracellular matrix ECM)-der ived growth and polarity signals. Retrovirally mediated expression of human papillomavirus type 16 (HPV-16) E6 and antisense oligodeoxynucleotides (OD Ns) were used to suppress p53 function in HMECs as a model of early breast cancer. p53(+) HMEC vector controls grew exponentially in reconstituted ECM (rECM) until day 6 and then underwent growth arrest on day 7. Ultrastructu ral examination of day 7 vector controls revealed acinus-like structures ch aracteristic of normal mammary epithelium. In contrast, early passage p53(- ) HMEC cells proliferated in rECM until day 6 but then underwent apoptosis on day 7. p53(-) HMEC-E6 passaged in non-rECM culture rapidly (8-10 passage s), lost sensitivity to both rECM-induced growth arrest and polarity, and a lso developed resistance to rECM-induced apoptosis. Resistance was associat ed with altered expression of alpha3-integrin. Treatment of early passage p 53- HMEC-E6 cells with either alpha3- or beta1-integrin function-blocking a ntibodies inhibited rECM-mediated growth arrest and induction of apoptosis. Our results indicate that suppression of p53 expression in HMECs by HPV-16 E6 and ODNs may sensitize cells to rECM-induced apoptosis and suggest a ro le for the alpha3/beta1 heterodimer in mediating apoptosis in HMECs grown i n contact with rECM.