Cytoplasmic trapping of CXCR4 in hepatocellular carcinoma cell lines.
OBJECTIVE
The chemokine receptor CXCR4 plays a role in the metastasis and progression of a broad range of malignant tumors; however, its influence on hepatocellular carcinoma (HCC) is not well defined. Thus, we analyzed the expression of CXCR4 and its functions in HCC cell lines in vitro.


METHODS
Five HCC cell lines (HepG2, Hep3B, SK-HEP-1, NCI-H630 and PLC/PRF5) were investigated. The CXCR4 expression was analyzed by RT-PCR, Western blotting, flow cytometry and immunofluorescence staining. In addition, the effects of stromal cell-derived factor-1 (SDF-1) on the migration, proliferation and survival of the cells were investigated, as well as the SDF-1-induced phosphorylation of signaling molecules.


RESULTS
All five cell lines had abundant CXCR4 in their cytoplasm, whereas a cell surface CXCR4 expression was only detected in a very small population of PLC/PRF5 cells. In contrast, SDF-1 bound to all the cells. SDF-1 induced the phosphorylation of AKT and ERK1/2 in the PLC/PRF5 cells and the phosphorylation of Stat3, AKT and ERK1/2 in the Hep3B cells. Nonetheless, SDF-1 did not induce migration or proliferation in any of the cells, nor did it rescue the cells from serum deprivation-induced apoptosis. Recruitment of CXCR4 from the cytoplasm to the cell surface was not elicited by dexamethasone, proinflammatory cytokines or VEGF. Hypoxia increased both the cytoplasmic and cell surface expressions of CXCR4 in only the PLC/PRF5 cells.


CONCLUSIONS
CXCR4 is trapped in the cytoplasm and it is not recruited to the cell surface by standard extrinsic stimuli in the majority of HCC cell lines, and the result of this is a negligible response to SDF-1.
Kim
Seong-Woo
SW
Division of Hematology/Oncology, Department of Internal Medicine, College of Medicine, Chungnam National University, Daejeon, Korea.
Kim
Ha-Yon
HY
Song
Ik-Chan
IC
Jin
Seon-Ah
SA
Lee
Hyo-Jin
HJ
Yun
Hwan-Jung
HJ
Kim
Samyong
S
Jo
Deog-Yeon
DY
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