OBJECTIVETo screen for novel gene(s) associated with tumor metastasis, and to investigate the effect of overexpression of phosphoprotein associated with glycosphingolipid microdomains 1 (PAG1) on the biological behaviors of human prostatic cancer cell line PC-3M-1E8 in vitro.

METHODSFour cDNA microarrays were constructed using cDNA library of prostatic cancer cells PC-3M-1E8 (high metastatic potential), PC-3M-2B4 (low metastatic potential), lung cancer cells PG-BE1 (high metastatic potential)and PG-LH7 (low metastatic potential)to screen genes which were differentially expressed according to their different metastatic properties. From a battery of differentially expressed genes, PAG1, which was markedly downregulated in both high metastatic sublines of PC-3M and PG was chosen for further investigation. Real-time PCR and Western blot were used to confirm the gene expression of PAG1 at mRNA and protein levels. Full-length coding sequence of human PAG1 was subcloned into plasmid pcDNA3.0 and the recombinant plasmids were stably transfected into PC-3M-1E8. The cell proliferation ability, anchorage-independent growth, cell cycle distribution, apoptosis rates and invasive ability were detected by MTT, and in addition, soft agar colony formation, flow cytometry analysis and matrigel invasion assay using Boyden chamber were also carried out respectively. All experiments contained pcDNA3.0-PAG1-transfected clones, vector transfected clones and non-transfected parental cells.

RESULTSA total of 327 differentially expressed genes were obtained between the high and low metastatic sublines of PC-3M cells, including 123 upregulated and 204 downregulated genes in PC-3M-1E8. A total of 281 genes, including 167 upregulated and 114 downregulated genes were obtained in PG-BE1 cells. Nine genes were simultaneously downregulated and 8 genes were upregulated in both high metastatic cell lines of PC-3M and PG. The expression of PAG1 at mRNA and protein level were decreased in the high metastatic subline PC-3M-1E8. Western blot revealed that PAG1 protein was downregulated in PC-3M-1E8 cell line which was in agreement with the gene expression at mRNA level. The proliferation ability and clonogenicity of PAG1 overexpression cells by stable transfection were markedly decreased in comparing with that of the control cells (P < 0.05). Colonies formed in stably PAG1-transfected cells, the vector-transfected clones and parental cells were 26.7 ± 5.2, 47.2 ± 3.2 and 52.3 ± 3.4 respectively (P < 0.05). Flow cytometry analysis showed that the stable PAG1-transfected cells at G₀-G₁ phase were significantly more than that of the control cells (P < 0.05). However, no difference of the apoptosis rate was found between PAG1-transfected cells and control cells (P > 0.05). The number of cells passing through the matrigel and multipore membrane was also decreased in the stable PAG1-transfected cells (35.1 ± 4.9) compared with those of the vector-transfected clones (127.6 ± 6.6) and parental cells (135.0 ± 5.0, P < 0.05).

CONCLUSIONSUsing cDNA microarray technique and differential gene expression analysis of sublines of the parental cancer cell lines enable of revealing the metastasis-related genes, among which PAG1 represents one of those under-expressed genes in the high metastatic subline PC-3M-1E8. Transfection expression of PAG1 suppresses cell proliferation, anchorage-independent growth and invasive ability of PC-3M-1E8 cells in vitro. Conclusively, PAG1 may play an important role in inhibiting the proliferation, invasion and metastasis of the cancer cells.