Independent and Associative Functions of IKKs and c-Myc in Cancer

Abstract

Cancer related mortality rate is exceptionally high in developing countries including Pakistan. Lack of awareness regarding early warning signs and potential risk factors often contributes to high mortality rate. Complex molecular mechanisms are involved in the pathogenesis of various malignancies. Nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) is one of the key pathways involved in cancer progression by cellular and immune regulation. This pathway is usually kept inactive in cytoplasm of normal cells by another group of proteins known as inhibitor of NF-κB (IκB). Degradation of IκB is regulated by a set of proteins called IκB kinases (IKKs) resulting in deregulated activation of NF-κB pathway in malignant cells. IKKs have been reported to interact with cellular Myelocytomatosis (c-Myc), thereby suggesting NF-κB-independent roles of IKKs in tumors. Fluorescence Resonance Energy Transfer (FRET) microscopy was employed to analyze the association of IKKs and c-Myc in human embryonic kidney (HEK 293) cell line. The current study revealed for the first time that the helix loop helix (HLH) and leucine zipper (LZ) domains of IKKα play an indispensable role in the interaction of IKKα with c-Myc. Further the effect of the IKKs and c-Myc interaction was tested at transcriptional and translational levels. IKKs were not found to affect the c-Myc expression at transcriptional and translational level, but IKKs were found to reduce transcriptional activity of c- Myc, thereby suggesting a possible regulatory role of IKKs on c-Myc and cancer. The interaction of IKKα with c-Myc was found to be comparatively stronger as compared to IKKβ. Therefore, in order to explore the independent role of IKKα in Breast cancer, the paraffin embedded tissue sections were immunohistochemically stained with IKKα. The immunohistochemical analysis of IKKα protein showed its decreased expression in Progesterone receptor (PR) positive BC biopsies suggesting an inverse correlation between the two proteins. An association between IKKα expression with tumor grade was observed but was found to be statistically insignificant. Abstract xxii Proto-oncogenes such as c-Myc are often found to be up-regulated in most of the human neoplasmas often in association with genetic changes including single nucleotide polymorphism (SNPs). Therefore, the effect of 27 non synonymous SNPs (nsSNPs) on the structure and function of c-Myc protein was found through an in silico analysis. Among the various nsSNPs studied; rs114570780 (Tyr47His), rs150308400 (Cys148Tyr), rs137906262 (Leu159Ile) and rs200431478 (Ser362Phe) were found to have noteworthy biological worth and may be considered while developing personalized therapeutic approaches. Taken together, these findings have potential implications in the development of diagnostics and therapeutic approaches against malignancies.