**7. Conclusion**

214 Hepatocellular Carcinoma – Basic Research

mitogen/extracellular protein kinase kinases, MEK-1 and MEK-2. MEK proteins then phosphorylate the downstream extracellular signal-regulated kinase (ERK) signaling molecules, ERK-1 and ERK-2. GTPase-Ras is a switch protein which alternates between an active on state with a bound GTP and an inactive off state with a bound GDP (Polakis & McCormick, 1992). Activation of ERK-1 and ERK-2 regulates many target proteins and gene regulation proteins in cytoplasm and nucleus. Ras protein of this pathway is found to involve other signaling pathways such as phosphoinositol-3-kinase/Akt pathway, Phospholipase C/protein kinase C pathway and Ral guanine nucleotide dissociation

The c-raf.1 is a direct downstream effector of ras. The signaling molecule c-raf.1 is one of the three highly conserved members (raf A, raf B and c-raf.1) of the raf gene family, which code for serine threonine-specific protein kinases in ras-mediated signal transduction pathway (Daum et al., 1994; Rapp, 1991; Sebolt-Leopold, 2000). The c-raf.1 has a crucial role in diverse signal transduction pathways (Rapp, 1991). The c-raf.1 protein kinase has oncogenic potential and is found to be up-regulated in tumors (Störm SM et al. 1993; Stanton VP Jr et al. 1987) and highly expressed in hepatocellular carcinoma too (Rapp,1991; Störm et al., 1993). An excessive activation of the MAPK pathway was observed in hepatocellular carcinoma (Rapp,1991). This findings and another findings that shows overexpression of c-raf in hepatocellular carcinoma in all the 30 different tissue specimens as tested by Hwang et al. (Hwang et al., 2004) thus suggest the predominant role of the raf protein as well as ras/raf/MEK/ERK/MAP kinase pathway in hepatocellular carcinoma. In a phase-wise study (initiation/ promotion/ hepatocellular carcinoma) in rat hepatocarcinogenesis model (Mukherjee et al., 2007), we

Fig. 8. A predominant raf-expressed late basophilic lesion (shown by arrows) in animal of

cancer control group. (Das et al. 2009)

stimulator pathway.

Unlike IGF II, c-raf.1 overexpression was observed in the late basophilic lesions associated with hepatocellular carcinoma. Thus, IGF II may have a role in activation of c-raf.1 signaling in the late stage of development of cancer. The role of raf.1 protein in IGF-induced signaling has been reported (Evert et al., 2004). But, when does it happen during the process of development of hepatocellular carcinoma? The c-raf.1 gene overexpression was predominantly found in hepatocellular carcinoma and late basophilic foci. Thus, the overexpression of c-raf.1 has been considered as a late-stage phenomenon during hepatocarcinogenesis (Bannasch, 2010). However, overexpression of c-raf.1 in very early lesion was also reported (He & Gascon- Barre, 1997). In our study, the dissection of animals after 7-8 weeks of carcinogenic insult did not show any raf.1-expressed lesions. Further, it was reported that c-raf.1 expressed in the basophilic tumors (Hwang et al., 2004). IGF II gene overexpression was noticed in the preneoplastic lesions and in hepatocellular carcinoma. On the other hand, overexpression of c-raf.1 gene was seen in the basophilic lesions associated with hepatocellular carcinoma as well as in tumor. While correlating the expression patterns of IGF II and c-raf.1, it suggests that IGF II-induced cellular signaling may be mediated through and/or affected by c-raf.1 in hepatocellular carcinoma and in the late stage of development of cancer. Thus, IGF II mediated c-raf.1 activation may drive late preneoplastic lesions towards neoplasia.
