MK2 signaling in STAT3-driven breast cancer

Despite recent advances, certain types of highly invasive breast cancer are not adequately addressed by current treatments. Approximately 60% of breast cancers are estrogen receptor (ER)-positive and can be treated with drugs that target ER, known as selective estrogen receptor modulators (SERMs, ex. Tamoxifen, Raloxifene). By contrast, the remaining 40% of breast cancers are ER-negative, resistant to SERMs, and associated with poor prognosis. The current treatment for ER-negative breast cancer is a blunt instrument; toxic chemotherapy that targets all rapidly dividing cells with little specificity. Specific, effective treatments targeting ER-negative cancers remain to be developed. An attractive molecular target for ER-negative breast cancer is signal transducer and activator of transcription-3 (STAT3); a number of studies have demonstrated high STAT3 activity in ER-negative breast cancers, and link STAT3 activity to cancer cell survival and metastasis. We have recently discovered a new molecular mechanism of STAT3 activation involving a kinase, MK2, which positively regulates STAT3 activity by specifically inactivating a well-known negative regulator, TRIM28. The role of MK2 and TRIM28 in regulating STAT3 activation in human breast cancer tissue remains unexamined, so we propose initial studies to examine the activity of these factors in breast cancer tissues. Furthermore, preliminary investigations reveal that a drug inhibitor of MK2 impairs the growth of ‘STAT3-addicted’ ER-negative breast cancer cells. Together, these studies have the potential to identify new breast cancer biomarkers, and inform the application of drug inhibitors of MK2 to target STAT3-driven ER-negative breast cancers. Fully characterize MK2-TRIM28-STAT3 signaling in breast cancer cell lines.We have confirmed published reports that STAT3 is constitutively activated in ER-negative breast carcinoma cell lines. We will explore the activity of MK2/TRIM28 in constitutive STAT3 phosphorylation in these cells and primary human mammary epithelial cells (HMECs) by immunoblotting and immune-complex kinase assays. STAT3 target gene expression will be investigated by RT-qPCR.Investigate the effects of MK2 inhibition on breast cancer cell proliferation.We hypothesize that inhibition of MK2 with a selective chemical inhibitor will decrease the levels of phosphorylated TRIM28, and allow TRIM28 to antagonize STAT3 activity. Preliminary investigations in our lab demonstrate that incubation of breast carcinoma cell lines with a drug inhibitor of MK2 selectively kills cells with high STAT3 activity (MDA-MB-468), but does not affect cells with low STAT3 activity (MCF-7). We propose to fully characterize the effects of MK2 inhibitors on STAT3 activity and determine the mechanism of MK2-inhibitor mediated cell death in STAT3-addicted breast cancer cells.Assess the status of MK2-TRIM28-STAT3 in patient-derived breast carcinoma tissue.We hypothesize that MK2 and TRIM28 may play important roles in STAT3 deregulation in breast cancer. To test this hypothesis, we will stain serial sections of normal mammary tissue as well as breast carcinoma tissue for immunohistochemistry with phospho-specific antibodies. If there is a significant correlation between STAT3 phosphorylation and MK2/TRIM28 phosphorylation in breast carcinoma tissue, we will evaluate the utility of p-MK2/p-TRIM28 as breast cancer biomarkers.