Abstract 4608: Overexpression of PKCα alters gene expression pattern in T47D breast cancer cells associated with hormone-independent growth and tamoxifen resistance

Abstract

Abstract Background: Tamoxifen (TAM) resistant breast cancer is a major obstacle in the clinical management of breast cancer and the mechanisms are not fully understood. Our lab has previously shown that overexpression of protein kinase C α (PKCα) in T47D breast cancer cells leads to a hormone-independent and TAM-resistant phenotype (Chisamore et. al., 2001, Clin. Cancer Res.7:3156-3165). Furthermore, we found that PKCα overexpression correlates with TAM-resistance and disease recurrence in patients (Tonetti et. al., 2003, Br. J. Cancer 88:1400-1402). Taken together, these findings suggest overexpression of PKCα is important in the progression of breast cancer to a hormone-independent and TAM-resistant phenotype. Methods: To determine the mechanism whereby overexpression of PKCα can mediate this progression, gene expression profiles of T47D: A18/neo and T47D: A18/PKCα cells following treatment with 0.1% EtOH or 10 nM 17β-estradiol (E2) for 24 hours were compared utilizing the Affymetrix Human Gene ST 1.0 Array. Total RNA was harvested for cRNA labeling and hybridization to Affymetrix ST 1.0 GeneChips. Data was analyzed using Partek Genomics statistical package (Partek, Inc). ANOVA test was used to calculate significance of the differential expression. Gene Ontology (GO) term enrichment was carried out using the Functional Annotation Clustering tool in DAVID Bioinformatics Database. Results: The basal expression of more than one thousand genes are differently expressed in T47D cells just by overexpressing PKCα, including genes related to cell cycle progression, gene expression regulation, protein transport and localization and metabolic processes. Interestingly, many of the E2-regulated genes in T47D: A18/neo cells have similar expression patterns in T47D: A18/PKCα cells in the absence of E2 treatment. Thirty six genes are up regulated by E2 in T47D: A18/neo cells and they have higher basal expression levels in T47D: A18/PKCα cells compared with T47D: A18/neo cells, including TFF1, CXCL12, STC2 and MYC. On the other hand, seventy six genes are down regulated by E2 in T47D: A18/neo cells that also have lower basal expression levels in the PKCα-overexpressing cells compared to T47D: A18/neo, including ERBB2, TGFB2 and TGFB3. Furthermore, E2 does not have a great influence on the gene expression levels in T47D: A18/PKCα cells. Conclusion: These results suggest that PKCα overexpression may lead to estrogen-independent activation of ER target genes and result in a pattern of gene expression similar to that in T47D cells treated with E2. This altered activation of ER by PKCα may lead to a gene expression pattern that mediates the progression to the estrogen-independent growth and TAM resistance. Pharmacological inhibition of this progression by inhibiting PKCα may offer treatment options for TAM-resistant breast cancer. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 4608.