Hepatocellular carcinoma (HCC) is the most common and highly lethal form of liver cancer, yet the molecular mechanisms underlying HCC pathogenesis remain poorly understood. Interestingly, disruption of metabolic regulation is frequently observed in HCC patients, suggesting that it may play a causative role in HCC initiation and/or progression. Metabolic regulation principally relies on transcriptional control ad our lab has discovered that Steroid Receptor Coactivator (SRC) family members are major regulators of metabolic gene transcription. In particular, SRC-2 deletion perturbs liver metabolic function through aberrant regulation of gluconeogenesis and bile acid export. My preliminary data suggests that SRC-2 acts as a hepatic tumor suppressor with loss of SRC-2 increasing liver carcinogenesis following diethylnitrosamine (DEN) injection as compared to SRC-2+/+ controls. Recently, we also found that SRC-2 deficiency significantly disrupts the central and peripheral circadian clocks causing abnormal cycling of known circadian and diurnal metabolic genes. Additionally, SRC- 2 can co-activate the primary circadian heterodimeric transcription factor complex Bmal1: clock;and preliminary analysis of liver SRC-2 ChIP-Seq data reveals that SRC-2 and Bmal1 share many targets including those involved in hepatic metabolism and stress response pathways. Previous publications indicate that loss of critical circadian genes including Bmal1, Per1/2, and Cry1/2 results in inapt energy regulation and spontaneous liver tumorigenesis. This proposal aims to better understand the overarching effects of SRC-2 as a tumor suppressor. I plan to investigate the molecular impact of SRC-2 ablation on the circadian clock in Specific Aim 1 by comparing RNA and protein expression of key circadian and circadian controlled metabolic and stress response genes from liver tissue in entrained SRC-2+/+ and SRC-2-/- animals. Additionally, I will investigate possible differences in plasma glucose, bile acid, triglyceride, and hepatic stress markers in entrained SRC- 2+/+ and SRC-2-/- animals. We plan to further investigate the potential interactions of SRC-2 with circadian transcription factor via co-immunoprecipitation and chromatin immunoprecipitation assays.
Specific Aim 2 will investigate the effect of chronic circadian disruption on hepatic stress and tumorigenesis in SRC-2+/+ and SRC-2-/- animals measuring tumor incidence, performing histology for stress markers, and measuring plasma markers of hepatic stress. With the increasing prevalence of HCC, it is imperative that we understand the molecular mechanisms linking circadian rhythms with carcinogenesis. As a well-established energy coregulator, SRC-2 may serve as a primary regulator of the circadian clock and a hepatic tumor suppressor synchronizing hepatic metabolism with the central clock. Therefore, I hypothesize that SRC-2 is an essential hepatic tumor suppressor necessary for regulation of circadian transcription factors to maintain metabolic synchrony in the liver and expect that loss of SRC-2 disrupts the circadian clock causing aberrant metabolic signaling, leading to hepatic stress and eventual hepatocellular carcinoma.
This project aims to meet the goals of the NIH and NCI to improve our understanding of cancer molecular biology and potentially develop therapeutics in the treatment of liver cancer. This proposal studies Steroid Receptor Co-activator 2 as a potential hepatic tumor suppressor involved in circadian regulation of metabolism.
