Loss of chemokine SDF-1 alpha-mediated CXCR4 signalling and receptor internalization in human hepatoma cell line HepG2

Expression of the chemokine stromal cell-derived factor-1 alpha (SDF-1 alph a) is absent from many carcinomas, including hepatomas. We note an early si gnalling defect in the hepatocellular carcinoma (HCC) cell line HepG2 that expresses the CXCR4 receptor and binds biotin-labelled SDF, but fails to st imulate downstream signalling events after engagement with SDF. In HepG2, t he SDF/CXCR4 interaction did not result in calcium influx. phosphorylation and internalization of CXCR4, nor in a rapid phosphorylation of p44/42 MAP kinase. There were no CXCR4 mutations in the second chemokine binding loop or C terminal phosphorylation and internalization domains. The downstream s ignalling machinery in HepG2 appears to be intact since transfection of wil d-type CXCR4 restored functional responsiveness. We conclude that HepG2 is unresponsive to SDF stimulation because of a defect located after receptor binding but before the activation of the signalling cascade. A hypothetical blocking molecule could hinder receptor internalization or CXCR4 signallin g. (C) 2001 Elsevier Science Inc. All rights reserved.