Investigation of Epigenetic Regulation of Tumor Suppressor Genes by Inhibition of Histone Deacetylases and Lipid Raft Signaling in Human Cancers

Abstract

Tumor development and cancer progression are principally guided by predominant role of oncogenes over tumor suppressor genes. Rejuvenation of tumor suppressor genes (TSGs) could be one of the therapeutic strategies against cancer. This thesis attempts to illuminate the regulatory mechanism behind TSG silencing by targeting histone deacetylases (HDACs) and lipid raft signaling. In view of dynamic and reversible nature of histone acetylation and overexpression of HDAC enzymes in cancer, HDACs were targeted by inhibitors that owe the ability to restore the expression of TSGs. The present thesis elucidates a novel property of Thymoquinone (TQ), an active principle of Nigella sativa, as an efficient inhibitor against histone deacetylases (HDACs). It reveals the molecular interaction of TQ with HDACs, especially HDAC1 and HDAC2. TQ could efficiently reactivate the expression of p21, maspin, insulin like growth factor binding protein7 (IGFBP7) and microtubule-associated tumor suppressor gene (MTUS1).

The epigenetic regulation of IGFBP7 in breast cancer has neither been studied adequately nor has its connection with lipid raft been investigated previously. This study reveals that downregulation of IGFBP7 is mostly due to histone modifications rather than DNA methylation in breast cancer. Perturbation of signaling pathways is one of the quintessential factors responsible for aberrant expression of TSGs in cancer. Therefore, modulation of IGFBP7 by lipid raft signaling is examined in breast cancer. It is apparent that lipid raft/RAS-MAPK signaling is involved in epigenetic regulation of IGFBP7 gene.

The role and regulation of MTUS1 in lung cancer is still in its infancy. The study delineates that the regulation of MTUS1 is independent of lipid raft inhibition. However, epigenetic mechanism plays a crucial role in its regulation. Human Males absent on the first (hMOF) and DNA methyltransferase 1 (DNMT1) are frequently over expressed in lung cancer. It is apparent from the results in the thesis that both DNMT1 and hMOF may be correlated with MTUS1 silencing in lung cancer. Further experiments through inhibition of DNMT1 and hMOF demonstrated the expression of MTUS1, which in turn attenuate proliferation and migration of lung cancer cells. Taken together this thesis emphasized TQ as an inhibitor of HDACs that helps expression of TSGs, like p21, Maspin and Bax and describes the importance of lipid raft signaling and epigenetic modulation of IGFBP7 and MTUS1.