Oncogene-induced NAD+ depletion in tumorigenesis

A proto-oncogene (hereafter simplified as oncogene) has the potential to initiate cancer. Oncogenes are often mutated and/or their products are expressed at high levels in various types of cancer. Several mechanisms and features of oncogenesis have been extensively discussed in the review of Hanahan and Weinberg “hallmarks of cancer: the next generation” [1]. Fundamentally, oncogenes give an unlimited proliferative advantage to cells which generates replicative stress and, leads to the genetic heterogeneity of the cell population. Thus, cancer is the disease of the genome and, targeting the terminal phase often results in cancer recurrence. Several ongoing preclinical studies and clinical trials propose to target the proliferation process [2,3]. Specific inhibitors of the replicative stress were successfully validated for cancer treatment in mice [4]. This type of therapy clearly induces cancer cell death but unfortunately creates an irreversible genotoxic stress in healthy cells, which may lead to their transformation, consequent cellular dysfunctions and secondary cancer. There is a clear need of developing new therapies. Understanding the critical early event and dissecting the step-wise progression of tumorigenesis would help us to design more efficient therapeutic interventions to prevent and treat cancer. In particular because, metabolic alterations are common fundamental characteristics of oncogenes and in this context, represent an essential hallmark of cancer, tackling primary metabolic defects can be an elegant approach to prevent and cure cancer. We summarize in this short editorial a recent example reported in Tummala et al. of how targeting the metabolic defects prior to the high cellular proliferation and DNA damage can eradicate hepatocellular carcinoma (HCC) and prevent pancreatic cancer development [5]. HCC is the most frequent primary liver neoplasm which often arises in the predisposing liver disease states. HCC accounts for approximately 800,000 deaths each year and, making it the second most lethal cause of cancer worldwide (GLOBOCAN 2008 v2.0). Various therapeutic approaches to the treatment of advanced HCC have been unsuccessfully implemented. One of the most beneficial HCC treatment is so far the well known kinase inhibitor Sorafenib that improves patient survival of a maximum of 2 to 3 months [2,6]. Thus, limited and inefficient therapeutic options render the curative treatment of the disease almost impossible. Although several pathways and molecular players were reported in HCC development, the lack of animal models that recapitulate the full spectrum of the human disease progression may impede the development of suitable therapies. Despite detailed etiological and clinical features, the pathogenesis of HCC is not well understood. The comprehension of the disease, identifying clinically relevant therapeutic targets and the generation of efficient medicines require powerful genetic tools that mimic the human clinical stages. In a recent study of our lab, we generated genetically engineered mouse models (GEMMs) of Unconventional prefoldin RPB5 interactor (URI) lossand gain-of-function [5,7]. Development of tumors in the murine liver after ectopic URI expression in the whole body motivated us to study its role and function in liver disease. Hepatocytic specific URI expression leads to spontaneous, heterogenous and aggressive tumors after 65 weeks of age, through a multistep process that recapitulate the human features of HCC. We propose that URI is as an oncogene essential for liver tumorigenesis and, URI GEMMs represent unique genetic models to appropriately address the mechanisms of HCC development and explore novel therapeutic avenues. Editorial