Abstract
Abstract Several factors have been identified that influence epithelial-mesenchymal transition (EMT) in breast cancer cells. We previously reported that overexpression of protein kinase C α (PKCα) in breast cancer predicts tamoxifen resistant secondary tumors (Tonetti, 2003). In T47D breast cancer cells, stable overexpression of PKCα (T47D/PKCα) leads to hormone-independent growth as well as tamoxifen resistance (Chisamore, 2001). In our current study we report that PKCα overexpression increases the metastatic potential of breast cancer cells through induction of a nonclasssical EMT. T47D/PKCα cells are morphologically distinct from T47D/neo cells and do not retain the cuboidal structure of epithelial breast cancer cells. Overexpression of PKCα resulted in significantly induced migratory capabilities in the Boyden chamber assay and PKC activation by phorbol 12-myristate 13 acetate further enhanced T47D/PKCα cell migration. Pharmacological inhibition with the classical PKC inhibitor Go6976 significantly reduced the migratory capacity of T47D/PKCα cells. Transient siRNA-mediated knockdown of PKCα (120 h) significantly reduced both basal and NIH3T3 fibroblast conditioned media-induced T47D/PKCα cell migration. Levels of adherens junction proteins E-cadherin, α-E-catenin, β-catenin and p120-catenin were significantly downregulated in T47D/PKCα cells compared to T47D/neo cells as determined by western blot. Levels of E-cadherin protein were restored by more than 50% after 168 h of PKCα knockdown in T47D/PKCα cells. While SYBR green RT-qPCR revealed that E-cadherin transcripts were significantly higher in T47D/PKCα cells compared to T47D/neo control cells, there was no change in expression of β-catenin or α-E-catenin transcripts. However, p120-catenin transcripts were significantly lower in T47D/PKCα cells compared to T47D/neo cells. Treatment with the proteasomal inhibitor MG132 induces accumulation of E-cadherin but not p120-catenin. Taken together, these data suggest that PKCα may be responsible for EMT in breast cancer cells through upstream signaling that leads to transcriptional inhibition of p120-catenin and subsequent degradation of E-cadherin protein. Further, PKCα expression may not only be predictive of tamoxifen-resistance and hormone-independent growth but also of increased potential for metastasis. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 2339. doi:10.1158/1538-7445.AM2011-2339
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