A Study On The Expression Of Cdk3 In Colon Cancer And The Molecular Mechanism

Objective: To investigate the Cdk3 expression profile in coloncarcinogenesis and abnormal activation in the colon cancer, and identifythe mechanism of Cdk3 enhances cell malignant transformation throughmediating AP-1 activation involved in cell the mechanism ofcarcinogenesis.Methods: Using immunohistochemistry assay and in situhybridization assay, Cdk3 protein and mRNA expression were detected in22 cases of colon cancers, 22 cases of colonic adenomas and 24 cases ofcolonic polyps; To investigate that Cdk3 enhances cells transformation,plasmids of Cdk3, c-Jun and other constructs were transfected into 3T3Swiss albino cells, the cell transformation were detected using cell platefoci formation assay; Plasmids of Cdk3, c-Jun and AP-1 werecotransfected into HEK293 cells, AP-1 activity in the transfects weredetected using luciferase reporter gene assay to conform Cdk3 increasedAP-1 activity.Results: (1) The results of immunohistochemistry assay shows thatCdk3 protein expressed in cytoplast and cytoplasm of colonic polyps,colonic adenoma and colon cancer tissue, mainly expressed in cytoplasm.Image analysis revealed that the mean optical density of Cdk3 protein incolon cancer tissues (0.80±0.36) was significantly higher than that incolon polyps (0.48±0.22) and colon adenoma tissues (0.25±0.13) (P ＜0.05), the mean optical density of colonic adenomas was significantlyhigher than colon polyps (P＜0.05). (2) The results of in situ hybridizationassay shows that Cdk3 mRNA expressed in cytoplast and cytoplasm ofcolonic polyps, colonic adenoma and colon cancer tissue, mainlyexpressed in cytoplasm. Image analysis revealed that the mean opticaldensity of Cdk3 mRNA in colonic polyps (0.33±0.07), colonic adenomas(0.25±0.04) and colon cancer (0.26±0.08) have no significant difference(P＞0.05). But under the microscope, Cdk3 mRNA density in coloncancer tissue was higher than that in colonic polyps and colonicadenomas, these imply that Cdk3 play an important role in coloncarcinogenesis. (3) Cell plate foci formation assay, significantly more fociwere observed in cells transfected with H-ras+Cdk3 (53+12.7) comparedwith H-ras (34+14.7) alone (P＜0.05), the most foci were detected inH-ras+Cdk3+c-Jun (115±25.3) group in all other condition, significantlyfewer foci were in H-ras+Cdk3+c-Jun Mutant (52±8.5) thanH-ras+Cdk3+c-Jun group (P＜0.05). These data showed that Cdk3enhance cell foci formation through c-Jun. (4) Luciferase activity assay incontransfects with Cdk3, Cdk3-DN, AP-1 and c-Jun constructs showedthat AP-1 luciferase activity significantly increased in cells with Cdk3(11.87±3.48) compared with the group with Cdk3-DN (0.99±0.18) orCdk2 (0.97±0.31) and control (1.27±0.35) (P＜0.05). AP-1 luciferaseactivity significantly increased in cells with Cdk3+cyclin C (18.12±2.14) compared with the group with Cdk3-DN or control (P＜0.05)Conclusions: (1) Cdk3 expression in the course of coloncancerization gradual increases. (2) AP-1 activity is up-regulated byCdk3. (3) Cdk3 enhances H-ras-mediated cell malignant transformation.(4) Cdk3 may involve in colon carcinogenesis by increasing AP-1 activitythrough c-Jun. These data imply that Cdk3 up-regulates AP-1 activity.