HCC Specific Protein Network Involving Interactions of EGFR with A-Raf and Transthyretin: Experimental Analysis and Computational Biology Correlates.

BACKGROUND: The network interactions link human disease proteins to regulatory cellular pathways leading to better understanding of protein functions and cellular processes. Revealing the network of signaling pathways in cancer through protein-protein interactions at molecular level enhances our understanding of Hepatocellular Carcinoma (HCC). OBJECTIVE: A rodent model for study of HCC was developed to identify differentially expressed proteins at very early stage of cancer initiation and throughout its progression. METHODOLOGY: HCC was induced by administrating N-Nitrosodiethylamine (DEN) and 2-aminoacetylfluorine (2-AAF) to male Wistar rats. Proteomic approaches such as 2D-Electrophoresis, PD-Quest, MALDI-TOF-MS and Western blot analyses have been used to identify, characterize and validate the differentially expressed proteins in HCC-bearing animals vis-a-vis controls. RESULTS: The step-wise analysis of morphological and histological parameters revealed HCC induction and tumorigenesis at 1 and 4 months after carcinogen treatment, respectively. We report a novel protein network of 735 different proteins out of which eight proteins are characterized by MALDI-TOF-MS analysis soon after HCC was chemically induced in rats. We have analyzed four different novel routes representing the association of experimentally identified proteins with HCC progression. CONCLUSION: The study suggests that A-Raf, transthyretin and epidermal growth factor receptor play major role in HCC progression by regulating MAPK signaling pathway and lipid metabolism leading to continuous proliferation, neoplastic transformation and tumorigenesis.

A-Raf: A new star of the family of raf kinases.

The Ras-Raf-MEK-MAPK (mitogen-activated protein kinase)-signaling pathway plays a key role in the regulation of many cellular functions, including cell proliferation, differentiation and transformation, by transmitting signals from membrane receptors to various cytoplasmic and nuclear targets. One of the key components of this pathway is the serine/threonine protein kinase, Raf. The Raf family kinases (A-Raf, B-Raf and C-Raf) have been intensively studied since being identified in the early 1980s as retroviral oncogenes, especially with respect to the discovery of activating mutations of B-Raf in a large number of tumors which led to intensified efforts to develop drugs targeting Raf kinases. This also resulted in a rapid increase in our knowledge of the biological functions of the B-Raf and C-Raf isoforms, which may in turn be contrasted with the little that is known about A-Raf. The biological functions of A-Raf remain mysterious, although it appears to share some of the basic properties of the other two isoforms. Recently, emerging evidence has begun to reveal the functions of A-Raf, of which some are kinase-independent. These include the inhibition of apoptosis by binding to MST2, acting as safeguard against oncogenic transformation by suppressing extracellular signal-regulated kinases (ERK) activation and playing a role in resistance to Raf inhibitors. In this review, we discuss the regulation of A-Raf protein expression, and the roles of A-Raf in apoptosis and cancer, with a special focus on its role in resistance to Raf inhibitors. We also describe the scaffold functions of A-Raf and summarize the unexpected complexity of Raf signaling.