Biological Significance Of PI3K/AKT Signal Pathway And Related Gene Alteration In Gastric Cancer

PI3K/Akt signal pathway is found to be an important process, which may lie inthe center of cell growth regulation. After its activation by growth factors, it exertsregulation on cell cycle, proliferation and apoptosis, as well as the angiogenesis, thetelomerase activity and cell invasion, etc. In previous studies, variations of multiplegenes in PI3K/Akt pathway had been proved in carcinogenesis, and its relationship totumor initiation and developlent had been recognized.In our former studies, the expression pattern of gastric cancer (GC) genes was setup by Oligo microarray analysis, in which, the discrepant expression of PI3K and Aktfamily were found. After the building up of protein expression pattern in colon cancer,a relationship between Galetin-3/MFAP3L(a novel protein gene) and PI3K/Akt wasproved with high expression.In order to explore the expression changes of PI3K/Akt pathway related genes,PIK3CA, AKT2, Galetin-3 and their mutual relationship, RT-PCR, Western-blot andmicroarray IHC were used to testify their manifestation in gastric cancer cell lines andprimary stomach tumors. The results showed that: PIK3CA and its protein werehighly expressed in gastric cancer cell lines and primary tumor (higher mRNAexpression in primary tumors 70% 19/29, P=0.01); the MFAP3L, Galetin-3 proteinwere highly expressed in gastric cancer micro tissue array (IHC positively stainingrates:70.8%, 17/24, P=0.027; 64.0%, 16/25, P=0.017 respectively).Based on above results, PCR-DHPLC, DNA sequencing techniques were used todetect the point mutation and polymorphism of PIK3CA and AKT2 gene in the gastric cancer cell lines and tumor tissues. The results were as follows: A point mutation A→C in exon 1634 (gastric cell lines 10%, 1/10; tumor tissue 0%, 0/30) in PIK3CA gene;Another point mutation A→G in exon 2730 (gastric cell lines 30%, 3/10; tumor tissue3.3%, 1/30); A polymorphie locus in exon 652 of AKT2 gene with the frequency ofwild type A/A 98% (49/50), and frequency of mutation type G/G 2% (1/50). A pointmutation G→C in intron 43377 (gastric cell lines 10%, 1/10; tumor tissue 2%, 1/50);a polymorphic locus in intron 48877 with the frequency of wild type A/A 82% (41/50),and frequency ofhomozygote type A/G 18% (9/50).This study demostrated that in the PI3K/Akt signal pathway, the related genes ofPI3KCA, AKT2, MFAP3L and Galectin-3 had significantly high expression whichmay be closely related to the initiation of gastric cancer. PI3KCA gene had mutationhot spots while AKT2 gene was relatively conservative. This may suggest that thevariation of PI3KCA gene plays an important role on activation of kinase. Moreover,the high expression of PI3KCA's upstream gene MFAP3L and AKT2's downstreamgene Galectin-3 may suggest the mutual regulation among this gene group. Furtherstudies may be needed to clarify the above findings in future.