| The platelet-derived growth factors (PDGFs) and their receptors (PDGFRs) are involved in various steps of cancer development and progression. This has rendered them as major players in tumorigenesis and key targets in selective therapies of various cancer types including gastric cancer. The PDGFs and PDGFRs have also shown to be involved in drug resistance in cancer treatments, numerous gene fusions mainly in hematological malignancies, makers of treatment response of some cancer types, and prognostic indicators of some cancers.To summarize the substantial data accumulating in this research field, a meta-analysis study was undertaken to investigate the association between PDGFs/PDGFRs and clinicopathological features together with their prognostic significance in gastric cancer. Articles that reported PDGF and/or PDGFR in tissues of GC patients and showed survival studies of patients with or without PDGF and/or PDGFR status and/or compared the association of PDGF and/or PDGFR in various clinicopathological features were included in English published literature in February, 2017 or earlier were searched for in the PubMed database. Pooled odd ratios(OR) and hazard ratios(HR)estimates at 95% confidence intervals(CI) were calculated with the fixed or random effect Mantel-Haenszel model using review manager version 5.3 software. The I2 statistic or the fixed-effect Mantel-Haenszel model p-value was employed in the investigation of heterogeneity among studies. The random-effect meta-analyses were employed to account for heterogeneity among studies. Funnel plots using review manager version 5.3 software was used to investigate publication bias. The key results of the meta-analysis were following:1) Association between high or positive PDGFs/PDGFRs status and clinicopathological features of gastric cancer: Of the 13 studies involved in clinicopathological studies, a high or positive PDGF/PDGFR status was shown in nearly half of gastric cancer cases[49.8%(653/1312) were PDGF/PDGFR(+)] but statistically insignificant. Nine studies containing 10 datasets were included in the analysis of association between high or positive PDGF/PDGFR[PDGF/PDGFR(+)] and age together with gender demographic characteristics; 7 studies with 9 datasets were meta-analyzed to evaluate the association between PDGF/PDGFR(+) dichotomous set of degree of differentiation of gastric cancer, well-differentiated and poorly differentiated; 4 studies were involved in the evaluation analysis of the association between PDGF/PDGFR(+) dichotomous set- LSG and SSG; 5 studies containing 7 datasets were included in a meta-analysis of depth of tumor invasion which was categorized into T1 stage and >T2 stage dichotomous set; 5 studies with 7 datasets were meta-analyzed to evaluate the association between PDGF/PDGFR(+) dichotomous set of positive nodal metastasis and negative nodal metastasis in gastric cancer; 4 studies with 6 datasets were included in meta-analysis for the evaluation of association between PDGF/PDGFR(+) and TNM staged gastric cancer patients in dichotomous fashion of >TNM stage 2 and TNM stage 1. Pooled Odd ratio(OR) at 95% Cl for different groups of analysis were as follows: young and middle aged(<70)versus elderly aged(?70) (OR= 0.93, 95% Cl: 0.57-1.50. POR =0.76); males versus females (OR-1.43, 95% Cl: 1.05-1.94, POR=0.02); poorly differentiated versus well-differentiated (OR= 0.88,95% Cl: 0.52-1.50, POR=0.64); large tumor size group(LSG)>6cm versus small tumor size group (SSG) ?6cm (OR= 0.65, 95% CI: 0.34-1.23, POR =0.18); >T2 stage versus T1 stage (OR=2.24, 95% CI: 1.60-3.14, POR <0.00001); nodal metastasis versus no nodal metastasis (OR= 3.15,95% CI: 1.59-6.23, POIR=0.0010); TNM stage ? IT versus TNM stage I (OR= 3.55, 95% CI: 1.89-6.69, POR <0.0001). The above results showed that PDGFs and PDGFRS were highly expressed among gastric cancer patients, significantly associated with prognostic variables including gender, nodal metastasis, and TNM stages with pooled OR values that were greater than or equal to 2.2) mRNA/Protein expression of PDGFs/PDGFRs and gene mutation profile of PDGFR:The 13 studies included in the meta-analysis of clinicopathological features was employed in a subgroup analysis of mRNA expression level and protein expression level methods of PDGF/PDGFR together with gene mutation of PDGFR. Three studies were included in a subgroup analysis of mRNA expression level and 5 studies were included in a subgroup analysis of gene mutation. The remaining 5 containing 7 datasets were included in the protein expression level subgroup analysis. Among patients with mRNA expression level, gene mutation and protein expression level method of detection of PDGF/PDGFR, 44.9% (71/158), 28.5% (71/249)and 56.5% (511/905) were PDGF/PDGFR(+) respectively. The respective subgroup pooled OR for mRNA expression level, gene mutation and protein expression level and pooled OR across the three subgroups were (OR=0.67, 95% Cl: 0.43-1.04,POR=0.07), (OR=0.15, 95% CI: 0.05-0.45,POR=0.0008),(OR=1.70, 95% CI: 0.73-3.94,POR=0.22) and (OR=0.67, 95% CI: 0.34-1.32,POR=0.24). The results of this part of the analysis suggested that PDGFs and PDGFRS were highly expressed in gastric cancer. Furthermore, mRNA expression level and gene mutation detection of PDGF/PDGFR recorded lesser association of PDGF/PDGFR with gastric cancer whereas protein expression level detection method recorded a greater association.3) Association between high or positive PDGFs/PDGFRs status and Asian together with Western gastric cancer patients: The patients included in the clinicopathological and prognostic significance of high or positive PDGF/PDGFR status among gastric cancer patients were included in the subgroup analysis of the location of patients. With reference to clinicopathological characteristics, 9 studies containing 11 datasets with extractable OR was meta-analyzed in Asian patients, subgroup whilst the remaining 4 studies with extractable OR were included in western patients, subgroup analysis. Subgroup analysis of mRNA/protein level of PDGF/PDGFR together with the mutation of PDGFR between the Asian and Western patients showed an insignificantly lesser association of PDGF/PDGFR among gastric cancer patients (OR=0.67, 95% CI: 0.34-1.32, POR=0.24).4) Prognostic significance of high or positive PDGFs/PDGFRs status among gastric cancer patients: Six studies containing 7 datasets with extractable HR data were included in the subgroup analysis. Three studies were included in OS subgroup, and the remaining 3 studies with 4 datasets were included in RFS subgroup. Subgroup analysis of prognostic significance of high or positive PDGF/PDGFR status recorded an overall insignificant prognostic effect in an overall survival/relapse free survival subgroup and Asian/Western patients' subgroup, (HR=0.96, 95%CI: 0.50-1.84, PHR=O.90) and (HR=0.78, 95% CI: 0.59-1.03, PHR=0.09) respectively. There was a negative but insignificant prognostic effect in OS and Asian patients and a positive but insignificant prognostic effect in RFS and western patients.Now available evidence has shown that PDGFs/PDGFRs are closely related to the occurrence and development of gastric cancers, which is one of the hot focuses in targeting therapy of tumor. Both epithelial growth factor (EGFR) and PDGFR belong to the receptor tyrosine kinase(RTK) family, and the former has high homology with PDGFR. Previous study in our lab indicated that type ? cGMP-dependent protein kinase (PKG ?) inhibited EGFR activation dramatically. Based on it, this study investigated the inhibitory effect of PKG ? on PDGFR activation in gastric cancer cells and the related mechanism. The main results were as follows:1) Inhibitory role of PKG ? on PDGF-BB induced biological activity and the downstream pathways in gastric cancer cells: Western blotting was used to detect the expression profile of PDGFR? in human gastric epithelial cell line (GES-1) and gastric cancer cell lines (AGS,HGC-27,SGC-7901 and BGC-823). The result showed that the expression of PDGFR? was higher in gastric cancer cells than in epithelial cells,especially in AGS and HGC-27. AGS and HGC-27 cells were infected with Ad-PKG ? which encoded PKG ? cDNA and increased the expression of PKG ?. Then the cells were treated with 8-pCPT-cGMP, followed by PDGF-BB.The results showed that activated PKG ? inhibited the PDGF-BB-induced migration by utilizing Transwell migration assay. The data from the CCK8 kit indicated that activated PKG ? inhibited the PDGF-BB initiating proliferation. The result from Giemsa staining assay revealed that activated PKG ? antagonized the pro-apoptotic effect of PDGF-BB. Western blotting results showed that activated PKG ? decreased the expression of PCNA, MMP-7 and the ratio of Bcl-2/Bax. Western blotting also was applied to detect the phosphorylation of key molecular in down signaling transductions of MAPK and PI3K/Akt mediated pathways that were tightly related with migration and proliferation. The phosphorylation of MEK1/2, ERK1/2, PI3K and Akt were all inhibited by activated PKG ?. The above results suggest that PKG ? could inhibit the proliferation and migration stimulated by PDGF-BB in gastric cancer cells, antagonize the antiapoptosis effect of PDGF-BB. Finally, PKG ? blocked the triggering effect of PDGF-BB induction downstream signaling transduction of MAPK and PI3K/Akt.2) PKG ? inhibition on PDGF-BB induced activation of PDGFRp and the related mechanism: AGS and HGC-27 cells were infected with Ad-PKG ? and then the cells were treated with 8-pCPT-cGMP followed by PDGF-BB. Phosphorylation of PDGFR?(Tyr751)activated by PDGF-BB decreased in western blotting result. PKG ? could combine with PDGFR? in AGS cells infected with Ad-PKG ? by using co-immunoprecipitation assay. PKG ?was activated in Ad-PKG ? infecting AGS and HGC-27 cells by 8-pCPT-cGMP. The result from imunoprecipitation indicated that PKG ? increased the phosphorylation of serine/threonine residues of PDGFR?. The possible phosphorylation site was predicted by prediction software. Flag-tagged mutated plasmids PDGFR? (S643A) and PDGGFR?(S712A)were obtained by site-directed mutation. COS-7 cells were transfected with mutated plasmids, and then infected by Ad-PKG ?, followed by 8-pCPT-cGMP activating PKG?. The immunoprecipitation result revealed that serine/threonine phosphorylation of PDGFR? by PKG ? declined dramatically when serine 712 was mutated. The above results suggest that PKG? phosphorylated serine/threonine residue by combination with PDGFR?, and in turn, inhibited the activation of PDGFR?. And the serine 712 was the specific site phosphorylated by PKG ?.In conclusion, the results of meta-analysis of this study shows that PDGFs/PDGFRs are closely related to gastric cancer: highly expressed in tumor tissues and significantly associated with gender, nodal metastasis, and TNM stages of the tumors. The results of laboratory investigation shows that PKG ? can inhibit the activation of PDGFR? and its downstream signaling and biological activities through binding with PDGFR? and causing phosphorylation of Serine 712 of the receptor. |
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