REGULATION OF BENIGN AND MALIGNANT HEPATOCYTE GROWTH

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DESCRIPTION (provided by applicant): Hepatocellular cancer (HCC) leads to the death of more than 35,000 Americans annually in addition to being one of the leading causes of cancer death worldwide. Surgical resection is the best treatment available to patients with HCC but is a viable option for only 20-40% of those diagnosed. The failure to develop alternative treatments for HCC is due to our lack of understanding of the disease etiology at the cellular and molecular level. Previous reports from our laboratory have identified components of a mitogen activated protein kinase (MAPK) cascades as a focal point in processing signals of diverse origin including those associated with guanine nucleotide regulatory protein (C-protein) coupled and tyrosine kinase-linked receptors. Specifically, we have demonstrated altered expression and function of inhibitory G-proteins (Giproteins) in more than 80% of human HCC analyzed. Furthermore, activation of Gi-proteins in human and animal models of HCC leads to enhanced mitogenesis via a mitogen activated protein kinase (MAPK) cascade, an effect not observed in non-transformed hepatocytes. Other data from our laboratory demonstrate changes in hepatic insulin-like growth factor-I (IGF-l) expression in HCC and non-tumorigenic, histologically normal hepatic tissue in tumor burdened animals. Stimulation of HCC cells with IGF-l leads to increased cell mitogenesis via a MAPK pathway, an effect abrogated by inhibition of Gi-protein signaling.Based on these observations the central hypothesis of this proposal is that a MAPK cascade represents a focal link between transmembrane signals of diverse origin, regulation of which directly affects hepatic tumor proliferation at multiple levels and is intrinsically linked to the increased cell mitogenesis characteristic of HCC. It is the aim of this NIH-R01 First Award to "determine the mechanisms by which MAPK components regulate cell mitogenesis at the membrane, cytoplasmic and nuclear levels." Specifically we will (i) over-express constitutively active or dominant negative components of G-protein/IGF-l-MAPK signaling pathways in conjunction with specific pharmacological agents that stimulate or inhibit these pathways. These data will determine the role of C-protein subunits and TK-linked receptors and their associated second messengers in regulating cytoplasmic (MAPK) signaling pathways in HCC. (ii) determine the role of G-protein/IGF-l-MAPK pathways in regulating nuclear transcription factors and cell proliferation and survival in normal and transformed (HCC) hepatocytes.Because the mortality associated with HCC is so high, deciphering the mechanisms by which cell growth and tumor progression occurs is clearly of major clinical importance and significance. Accordingly, elucidation of the mechanisms controlling cell proliferation at the cytoplasmic and nuclear level represents a potential breakthrough in the development of new treatments for non-resectable HCC.