Renal cell carcinoma (RCC) is the most common form of kidney cancer with a limited number of treatment options for the metastatic form. RCC is categorized into various subtypes, with the clear cell RCC (ccRCC) encompassing close to 85% of all RCC tumors . The main risk factor for ccRCC is aberrations in the von Hippel Lindau gene (VHL) [2,3]. Inactivation of the VHL gene results in an increased expression of hypoxia- inducible factor alpha subunits (HIF1? and HIF2?), leading to constitutive activation of hypoxia pathways [4,5]. Poly(ADP-ribose) polymerase 1 (PARP-1)-regulated signaling contributes to the initiation and progression of various human malignancies . PARP-1 regulates transcription of HIF1?- and HIF2 ?-dependent genes, arguably the most critical event in the renal tumorigenesis [7,8]. Given that abnormal expression levels of HIF1? and HIF2? are the pivotal factors in renal tumorigenesis, PARP-1 inhibitors appear to be a promising strategy for the treatment of advanced renal malignancy. The clinical potential of PARP-1 inhibitors has been recognized over the past two decades, prompting intensive research on their therapeutic application , albeit not without some setbacks. Classical PARP-1 inhibitors were developed using the NAD-dependent route of PARP-1 regulation. Since NAD is an abundant and ubiquitous molecule used by numerous enzymes, inhibition of PARP-1 by competing with NAD tends to affect a number of other metabolic processes producing multiple off-target effects . By targeting the histone H4 route of PARP-1 activation, we?ve developed a new class of PARP-1 inhibitors. These inhibitors demonstrate superior in vitro and in vivo antitumor efficacy when compared to the classical NAD-like PARP-1 inhibitors. New PARP-1 inhibitors effectively target PARP-1 dependent transcription. The proposed experiments will examine the molecular mechanism coupling PARP-1 pathway with the induction and maintenance of the RCC malignancy. We will identify PARP-1 binding sites in promoters of RCC-associated genes and confirm that transcription of these genes is PARP-1/PARG-dependent. Our preliminary experiments have demonstrated that pADPr is overproduced in the RCC cells while production of PARG and E-Cadherin is lost. Using cell and animal models of human RCC, we will test whether these aberrations are required for the onset and maintenance of RCC malignancy. We propose the following Specific Aims:
Aim 1. To determine the effects of PARP-1 and PARG deregulation during the onset of RCC.
Aim 2. To investigate the role of PARP-1 localization in promoters.
Aim 3. To determine genomic sites of PARP-1 and poly(ADP-ribose) occupancy in RCC chromatin.
Our goal is to understand how a human cancer cell fine-tunes the induction of proto-oncogene activity by performing a quick, localized, and reversible transcription activation. We will pursue this goal by using the mammalian system of poly(ADP-ribose) metabolism as a model. Understanding how Poly (ADP-ribose) polymerase-1 acts within normal, undamaged chromatin will advance our knowledge of developmental gene regulation, and facilitate the development of new therapeutic drugs for treatment of diseases caused by metabolic deregulation, as well as of methods that allow re-programming genes experimentally.