Increasing evidence had suggested important roles of protein kinase C (PKC)-mediated phosphorylation of myristoylated alanine-rich C kinase substrate (MARCKS) in modulating various cellular processes, including cancer cell growth and metastasis. However, there is a lack of information regarding to the roles of MARCKS and its pSer 159/163 phosphorylated product in breast cancer cells and tissues. To tackle this concern, we recently initiated both immunohistochemical and western blot analyses on a series of clinical specimens and several breast cancer cell lines. We have observed a significant elevation of phospho-MARCKS associated with advanced-stage breast cancer tissues as compared with benign ones, particularly in triple-negative breast cancer (TNBC) tissues and cell lines. Knockdown of MARCKS expression resulted in suppressions of lamellipodia/filopodia formation and migration/invasion as well as down-regulation of Src activity in these TNBC cell lines. Of note, MARCKS-silenced TNBC cells grew much more slowly and more sensitive to paclitaxel than the control and parental cells. Treatment with paclitaxel was shown to induce MARCKS phosphorylation in a dose-dependent manner, which may be related to an enhanced paclitaxel resistance in some of TNBC cells. However, PKC inhibitors were able to abrogate paclitaxel-induced MARCKS phosphorylation. Consistent with this potential, treatments of TNBC cells with a MARCKS N-terminus sequence peptide, namely MANS, to down regulate PKC/MARCKS pathway not only attenuated the associated aggressive phenotype but also synergistically enhanced paclitaxel-induced cytotoxicity in vitro and in vivo. These results demonstrate an association of PKC-mediated MARCKS phosphorylation with breast cancer malignancy potential and MARCKS phosphorylation as a predictor of paclitaxel resistance in TNBC cells. It is suggestive that an inhibition of PKC/MARCKS pathway may serve as an alternative therapeutic strategy for enhancing efficacy of chemotherapy.

Citation Format: Ching-Hsien Chen, Muhammad Arif, Wen-Hsin Chang, Yuan Yuan, Jing Zhai, David K. Ann, Reen Wu. PKC/MARCKS pathway is a novel therapeutic target associated with breast cancer malignancy potential and paclitaxel resistance. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 2769. doi:10.1158/1538-7445.AM2014-2769