Abstract 4972: Investigating the role of Syk in TGF-β induced P-bodies and breast cancer metastasis
Authors: Shana D. Hardy, Robert L. Geahlen
Journal: Cancer Research (2015)

Abstract Regulation of mRNA translation and degradation is critical in the control of cell growth and survival. Translational control is often exploited by human cancers and is crucial to cancer development and progression. Translational control processes include mRNA degradation, mRNA surveillance, RNA gene silencing, and translational repression. These processes share several mRNA processing enzymes (mRNPs), all observed to co-localize in discrete cytoplasmic foci referred to as processing bodies (P-bodies). Specifically, it has been shown that colorectal cancer cells promote the assembly of P-bodies to control the translation of specific mRNAs using TGF-β/Smad signaling. TGF-β is a known driver of the epithelial to mesenchymal transition (EMT). This process contributes to the invasive and metastatic potential of breast cancer cells. Syk is an essential protein tyrosine kinase in immune cells but is also present in non-hematopoietic cells such as mammary epithelial cells. Syk appears to have more diverse roles that have not yet been elucidated. What has been observed, however, is lost of Syk expression in invasive breast carcinoma tissue / cell lines and that the reintroduction of Syk into metastatic breast cancer cells suppresses tumor growth and metastasis. We collaborated with Dr. Andy Tao's lab, which specializes in mass spectrometry technologies to identify potential Syk substrates in breast cancer cells. Among these substrates were proteins associated with P-bodies and involved in mRNA metabolic processes. These interactions lead us to hypothesize that Syk co-localizes with P-bodies. To investigate this we used fluorescent microscopy and biochemical methods. We induced P-body formation using several different stimuli that included MG132, Sodium Arsenite, and TGF-β and we observed Syk co-localizing within P-bodies in several cell models. Moreover, we observed tyrosine phosphorylation occurring in P-bodies in a Syk-dependent manner. Interestingly, we found that Syk-expressing cells displayed decreased average number of P-bodies when expose to oxidative stress. Apparently, the presence of Syk enhances P-body clearance, possibly influencing the integrity of P-body function. These findings prompted us to investigate the physiological role of P-bodies in breast cancer cells. We discovered that TGF-β induction of P-bodies increases with EMT. However, once cells are transformed, P-body formation is loss. Moreover, mRNA decaying enzyme and P-body component, Dcp1a decreases in more metastatic cells. When Dcp1a is over-expressed, which results in aberrant P-bodies, EMT is blocked. These findings suggest that the formation of P-bodies contribute to the EMT process. We are now investigating the relationship between Syk's role in the disassembly of P-bodies and its role as a tumor suppressor in breast cancer cells. We are also interested in understanding the mechanistic role for Syk in P-bodies and mRNA metabolism Citation Format: Shana D. Hardy, Robert L. Geahlen. Investigating the role of Syk in TGF-β induced P-bodies and breast cancer metastasis. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 4972. doi:10.1158/1538-7445.AM2015-4972