Loss of chemokine SDF-1alpha-mediated CXCR4 signalling and receptor internalization in human hepatoma cell line HepG2.
Expression of the chemokine stromal cell-derived factor-1alpha (SDF-1alpha) is absent from many carcinomas, including hepatomas. We note an early signalling defect in the hepatocellular carcinoma (HCC) cell line HepG2 that expresses the CXCR4 receptor and binds biotin-labelled SDF, but fails to stimulate downstream signalling events after engagement with SDF. In HepG2, the 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 signalling machinery in HepG2 appears to be intact since transfection of wild-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 signalling.
Mitra
P
P
Department of Biochemistry and Molecular Pharmacology, University of Massachusetts Medical School, Worcester, MA 01655, USA.
De
A
A
Ethier
M F
MF
Mimori
K
K
Kodys
K
K
Shibuta
K
K
Mori
M
M
Madison
J M
JM
Miller-Graziano
C
C
Barnard
G F
GF
D006528:Carcinoma, Hepatocellular; D054377:Chemokine CXCL12; D019743:Chemokines, CXC / Q000378:metabolism*; D015536:Down-Regulation / Q000502:physiology; D005434:Flow Cytometry; D015972:Gene Expression Regulation, Neoplastic; D006801:Humans; D019169:Jurkat Cells; D008113:Liver Neoplasms; D020935:MAP Kinase Signaling System / Q000502:physiology*; D019950:Mitogen-Activated Protein Kinase 1 / Q000378:metabolism; D048052:Mitogen-Activated Protein Kinase 3; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism; D010766:Phosphorylation; D019718:Receptors, CXCR4 / Q000235:genetics / Q000378:metabolism*; D017422:Sequence Analysis, DNA; D014162:Transfection
C515255:CXCL12 protein, human; D054377:Chemokine CXCL12; D019743:Chemokines, CXC; D019718:Receptors, CXCR4; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; D020928:Mitogen-Activated Protein Kinases