P53 but not cyclin E acts in a negative regulatory loop to control HER-2 expression in MCF-7 breast carcinoma cell line.

Cyclin E, HER-2 and p53, are considered as major prognostic markers in breast cancer. As they are related in patho-clinical level, we aimed to check if they have any direct interaction on expression of each other. To study the effect of cyclin E on HER-2 expression, cell lines stably overexpressing cyclin E or its low molecular weight (LMW) isoforms were generated. To understand the results of p53 silencing either alone or in combination with cyclin E overexpression, we created three different p53 stably knocked down cell lines. Protein expression was analyzed by western blot, HER-2 expression in the established cell lines were determined using SYBR green real time PCR and data analyzed by REST software. Results indicate that HER-2 expression is only downregulated following p53 silencing and none of cyclin E isoforms can alter its expression. The presence of cyclin E isoforms in p53 silenced clones also does not altered HER-2 expression. Given the fact that p53 degradation is increased by HER-2 overexpression, these data can draw a regulatory loop in which a non-mutated functional p53 and HER-2 can bidirectionally regulate the expression of these two genes. This study improves our understandings of these pathways and these proteins can be introduced either as a marker or as a target in cancer treatment.