Hepatoma cells from mice deficient in glycine N-methyltransferase have increased RAS signaling and activation of liver kinase B1.

Martínez-López N, García-Rodríguez JL, Varela-Rey M, Gutiérrez V, Fernández-Ramos D, Beraza N, Aransay AM, Schlangen K, Lozano JJ, Aspichueta P, Luka Z, Wagner C, Evert M, Calvisi DF, Lu SC, Mato JM, Martínez-Chantar ML
Gastroenterology. 2012 143 (3): 787-798.e13

PMID: 22687285 · PMCID: PMC3429651 · DOI:10.1053/j.gastro.2012.05.050

BACKGROUND & AIMS - Patients with cirrhosis are at high risk for developing hepatocellular carcinoma (HCC), and their liver tissues have abnormal levels of S-adenosylmethionine (SAMe). Glycine N-methyltransferase (GNMT) catabolizes SAMe, but its expression is down-regulated in HCC cells. Mice that lack GNMT develop fibrosis and hepatomas and have alterations in signaling pathways involved in carcinogenesis. We investigated the role of GNMT in human HCC cell lines and in liver carcinogenesis in mice.

METHODS - We studied hepatoma cells from GNMT knockout mice and analyzed the roles of liver kinase B1 (LKB1, STK11) signaling via 5'-adenosine monophosphate-activated protein kinase (AMPK) and Ras in regulating proliferation and transformation.

RESULTS - Hepatoma cells from GNMT mice had defects in LKB1 signaling to AMPK, making them resistant to induction of apoptosis by adenosine 3',5'-cyclic monophosphate activation of protein kinase A and calcium/calmodulin-dependent protein kinase kinase 2. Ras-mediated hyperactivation of LKB1 promoted proliferation of GNMT-deficient hepatoma cells and required mitogen-activated protein kinase 2 (ERK) and ribosomal protein S6 kinase polypeptide 2 (p90RSK). Ras activation of LKB1 required expression of RAS guanyl releasing protein 3 (RASGRP3). Reduced levels of GNMT and phosphorylation of AMPKα at Thr172 and increased levels of Ras, LKB1, and RASGRP3 in HCC samples from patients were associated with shorter survival times.

CONCLUSIONS - Reduced expression of GNMT in mouse hepatoma cells and human HCC cells appears to increase activity of LKB1 and RAS; activation of RAS signaling to LKB1 and RASGRP3, via ERK and p90RSK, might be involved in liver carcinogenesis and be used as a prognostic marker. Reagents that disrupt this pathway might be developed to treat patients with HCC.

Copyright © 2012 AGA Institute. Published by Elsevier Inc. All rights reserved.

MeSH Terms (32)

AMP-Activated Protein Kinases Animals Apoptosis Azacitidine Calcium-Calmodulin-Dependent Protein Kinase Kinase Carcinoma, Hepatocellular Cell Line, Tumor Cell Proliferation Cell Transformation, Neoplastic Cyclic AMP-Dependent Protein Kinases DNA Methylation Enzyme Activation Enzyme Inhibitors Glycine N-Methyltransferase Guanine Nucleotide Exchange Factors Humans Liver Neoplasms Mice Mice, Inbred C57BL Mice, Knockout Mice, Nude Mitogen-Activated Protein Kinase 1 Mitogen-Activated Protein Kinase Kinases Phosphorylation Protein-Serine-Threonine Kinases ras Proteins Ribosomal Protein S6 Kinases, 90-kDa RNA Interference Signal Transduction Time Factors Transfection Tumor Burden

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