Identification of carboxypeptidase of glutamate like-B as a candidate suppressor in cell growth and metastasis in human hepatocellular carcinoma

Purpose: We have previously done large-scale cDNA transfection screening on human hepatocellular carcinoma (HCC) cells and have identified 3,806 cDNA genes that possess the ability of either stimulating or inhibiting cell growth. In this study, we characterized one of these growth suppressor genes, Carboxypeptidase of glutamate like-B (CPGL-B), in HCC.

Experimental design: Semiquantitative reverse-transcription PCR was used to examine the expression levels of CPGL-B. The cellular localization and functions of CPGL-B were investigated by enforced expression of CPGL-B in HCC cells.

Results: From our previous cDNA transfection screening, we identified a gene named CPGL and its isoform, CPGL-B. With computational analysis, CPGL was located at chromosome 18q22.3 and was a homologue of peptidase family M20. CPGL was expressed in all adult and fetal tissues, whereas its isoform, CPGL-B, lacking exons 3 and 4, was expressed in all fetal tissues but only in liver and placenta of adult tissues. In HCC, CPGL-B was frequently underexpressed (35 of 90, 38.9%) in tumorous tissues compared with the corresponding nontumorous livers. Intriguingly, the underexpression was significantly associated with the presence of venous invasion (P=0.018) and tumor microsatellite formation (P=0.004). Stable transfection of CPGL-B in SMMC7721 HCC cells showed significant inhibition in cell viability, colony formation, cell invasion, and tumor formation in nude mice. CPGL-B also down-regulated CXCR3, matrix metalloproteinase 11, and CD44s, which are involved in cell growth and cell migration.

Conclusions: These findings suggest that the frequent underexpression of CPGL-B may be associated with cell growth and metastasis of HCC.