Proteins Involved in HDACi Induced Decay of ERBB2 Transcripts in Breast Cancer
ERBB2-positive breast cancer is an aggressive disease form that can result in rapid tumor growth and metastasis driven by the overexpression of ERBB2 growth factor receptors present on the cell surface. Currently, approved agents can target and disable ERBB2 receptor function, but as few as 30% of patients with disseminated ERBB2-positive breast cancer will respond to these targeted therapeutics when given as single agents. Even then, many initial responders will soon develop resistance to these agents. Histone deacetylase inhibitors (HDACi) are a powerful new class of epigenetic therapeutics that have demonstrated potent antitumor activity. However, there are several concerns that need to be addressed regarding the clinical usage of pan-HDACi therapeutics, such as the standard clinical prototype hydroxamic acid, trichostatin-A (TSA). These include the many genomic and non-genomic targets of pan-HDACi, the off-target side effects, and the lack of proven HDAC-dependent cancer pathways predictive of tumor responsiveness. Early observations in our laboratory have shown that in vitro TSA treatment of breast cancer cell line models promotes accelerated decay of polyribosomally associated ERBB2 mRNA, calling attention to a previously unrecognized transcript decay mechanism that could be exploited to develop new cancer therapeutics. Further studies have found that U-rich sequences in the 3’untranslated region (UTR) of ERBB2 transcripts are an important component of this transcript decay pathway. Based on these observations, we hypothesize that polyribosomally associated proteins, subject to regulation by HDAC-modulated protein acetylation, bind to the 3’UTR of ERBB2 mRNA within hours of TSA treatment, and mediate its rapid degradation. Using the ERBB2-overexpressing human breast cancer cell line SKBR3 and an ERBB2 3’UTR mRNA construct and assay designed to precipitate protein complexes, we attempt to identify proteins physically associated with and potentially mediating the polysome-associated ERBB2 mRNA decay pathway. Progress in this effort is expected to lead to a cancer treatment strategy more effective and selective than the use of pan-HDACi for the treatment to of ERBB2 overexpressing malignancies.
Breast Cancer, HER2, ERBB2, HDACi, SKBR3, hnNRPK, Biology
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