Interference with Activator Protein-2 transcription factors leads to induction of apoptosis and an increase in chemo- and radiation-sensitivity in breast cancer cells

<p>Abstract</p> <p>Background</p> <p>Activator Protein-2 (AP-2) transcription factors are critically involved in a variety of fundamental cellular processes such as proliferation, differentiation and apoptosis and have also been implicated in carcinogenesis. Expression of the family members AP-2α and AP-2γ is particularly well documented in malignancies of the female breast. Despite increasing evaluation of single AP-2 isoforms in mammary tumors the functional role of concerted expression of multiple AP-2 isoforms in breast cancer remains to be elucidated. AP-2 proteins can form homo- or heterodimers, and there is growing evidence that the net effect whether a cell will proliferate, undergo apoptosis or differentiate is partly dependent on the balance between different AP-2 isoforms.</p> <p>Methods</p> <p>We simultaneously interfered with all AP-2 isoforms expressed in ErbB-2-positive murine N202.1A breast cancer cells by conditionally over-expressing a dominant-negative AP-2 mutant.</p> <p>Results</p> <p>We show that interference with AP-2 protein function lead to reduced cell number, induced apoptosis and increased chemo- and radiation-sensitivity. Analysis of global gene expression changes upon interference with AP-2 proteins identified 139 modulated genes (90 up-regulated, 49 down-regulated) compared with control cells. Gene Ontology (GO) investigations for these genes revealed <it>Cell Death </it>and <it>Cell Adhesion and Migration </it>as the main functional categories including 25 and 12 genes, respectively. By using information obtained from Ingenuity Pathway Analysis Systems we were able to present proven or potential connections between AP-2 regulated genes involved in cell death and response to chemo- and radiation therapy, (i.e. <it>Ctgf, Nrp1</it>, <it>Tnfaip3, Gsta3</it>) and AP-2 and other main apoptosis players and to create a unique network.</p> <p>Conclusions</p> <p>Expression of AP-2 transcription factors in breast cancer cells supports proliferation and contributes to chemo- and radiation-resistance of tumor cells by impairing the ability to induce apoptosis. Therefore, interference with AP-2 function could increase the sensitivity of tumor cells towards therapeutic intervention.</p

Reprogramming of the ERR alpha and ER alpha Target Gene Landscape Triggers Tamoxifen Resistance in Breast Cancer

Endocrine treatment regimens for breast cancer that target the estrogen receptor-alpha (ER alpha) are effective, but acquired resistance remains a limiting drawback. One mechanism of acquired resistance that has been hypothesized is functional substitution of the orphan receptor estrogen-related receptor-alpha (ERR alpha) for ER alpha. To examine this hypothesis, we analyzed ERR alpha and ER alpha in recurrent tamoxifen-resistant breast tumors and conducted a genome-wide target gene profiling analysis of MCF-7 breast cancer cell populations that were sensitive or resistant to tamoxifen treatment. This analysis uncovered a global redirection in the target genes controlled by ER alpha, ERR alpha, and their coactivator AIB1, defining a novel set of target genes in tamoxifen-resistant cells. Beyond differences in the ER alpha and ERR alpha target gene repertoires, both factors were engaged in similar pathobiologic processes relevant to acquired resistance. Functional analyses confirmed a requirement for ERR alpha in tamoxifen-and fulvestrant-resistant MCF-7 cells, with pharmacologic inhibition of ERR alpha sufficient to partly restore sensitivity to antiestrogens. In clinical specimens (n - 1041), increased expression of ERR alpha was associated with enhanced proliferation and aggressive disease parameters, including increased levels of p53 in ER alpha-positive cases. In addition, increased ERR alpha expression was linked to reduced overall survival in independent tamoxifen-treated patient cohorts. Taken together, our results suggest that ER alpha and ERR alpha cooperate to promote endocrine resistance, and they provide a rationale for the exploration of ERR alpha as a candidate drug target to treat endocrine-resistant breast cancer. (C)2015 AACR