Studies On The Roles Of MiR-18a In Radiation-Induced Death In Colorectal Cancer Cell

Colorectal cancer is one of the most common maligncy of digestive tract with almostone million new diagnosed cases worldwide each year. Treatment of colorectal cancerinclude surgery, chemotherapy, radiation therapy and hormone therapy. Radiation therapyplays an important role in cancer therapy. However, due to the different responses toradiotherapy in population, treatment effects are limited. Therefore, improvingradiosensitivity becomes one of the significant problems in the current treatment ofcolorectal cancer.miRNAs are small (18-25nucleotide length)non coding RNA, which bind to3’UTR of target genes and up-regulate or down-regulate expression of target genes.Many studies have confirmed that miR-18a is highly expressed in a series of tumors,such as gastric cancer, liver cancer, colorectal cancer and other tumors, indicatng thatmiR-18a plays an important role in tumor. However, few studies have reported therole and machnism of miR-18a in radiation induced cancer colorectal cell death.Objective:To explore the role of miR-18a in ionizing radiation induced colorectal cancercell death, and the possible mechanism how miR-18a effect on colorectal cancer cellsensitivity to radiation. Our study aims at optimizing the clinical treatment ofcolorectal cancer and providing a theoretical basis of new therapeutic targets.Methods:(1) Human colorectal cancer cell line SW116and SW480were used in thisstudy;(2) qRT-PCR detected cellular expression of miR-18a;(3) Western Blotdetected changes of protein expressing level;(4) colony formation assay detectedcell sensitivity to radiation;(5) flow cytometry detected cell cycle, rate of apoptosiscell and rate of cell autophagy;(6) Quantity One software was used to calculate theband value. Result:1.Effects of miR-18a on IR induced cell death, cell cycle, apoptosis andautophagy in SW480cells(1).Effect of miR-18a on IR induced cell death in SW480cellsColony formation assay revealed that after IR treatment, cell viability of mimicgroup was increased compared with NC group; cell viability of inhibitor group didn’tchange a lot, suggesting that overexpression of miR-18a could decrease IR inducedcell death in SW480cells.(2).Effect of miR-18a on IR induced cell cycle in SW480cells.G2/M phase cell percentage of mimic+4Gy group was higher than NC+4Gygroup(p<0.05), G2/M phase cell percentage of NC+4Gy group was lower thanmimic group(p<0.05). The result indicated that miR-18a could suppress IR inducedSW480G2/M phase arrest.(3).Effect of miR-18a on IR induced apoptosis in SW480cells.Apoptosis rate in mimic+4Gy group was significantly higher than NC+4Gygroup. Apoptosis rate in NC+4Gy was1.26%higher than NC group, and apoptosisrate in mimic+4Gy group was0.38%higher than mimic group. Apoptosis rate inmimic inhibitor group didn’t change a lot compared with NC inhibitor group. Thissuggested that overexpression of miR-18a could suppress IR induced apoptosis inSW480cells.(4).Effect of miR-18a on IR induced autophagy in SW480cells.Compared with NC group, autophagy rate in mimic group was slightly increased;after IR treatment, autophagy rate in mimic+4Gy group was significantly lower thanNC+4Gy Group.Compared with NCi group, autophagy rate in inhibitor+4Gy wassignificantly higher than NCi+4Gy group(p<0.05). The result suggested thatoverexpression of miR-18a could suppress IR induced autophagy in SW480cells.2. Effects of miR-18a on IR induced cell death, cell cycle, apoptosis andautophagy in SW116cells(1).Effect of miR-18a on IR induced cell death in SW116cellsColony formation assay revealed that after IR treatment, cell viability of mimicgroup was decreased compared with NC group(p<0.05), suggesting thatoverexpression of miR-18a could increase IR induced cell death in SW116cells.(2).Effect of miR-18a on IR induced cell cycle in SW116cells.G2/M phase cell percentage of NC+4Gy group was4.25%higher than NC group. G2/M phase cell percentage of mimic+4Gy group was8.71%higher thanmimic group. The result indicated that overexpression of miR-18a could enhance IRinduced G2/M phase arrest in SW116cells.(3).Effect of miR-18a on IR induced apoptosis in SW116cellsCompared with NC group, apoptosis rate in mimic group was significantlyincreased; after treatment of IR, apoptosis rate in mimic+4Gy group was significantlyhigher than NC+4Gy group. This suggested that expression of miR-18a could induceapoptosis in SW116cells.(4).Effect of miR-18a on IR induced autophagy in SW116cells.Autophagy rate in NC+4Gy group was significantly3.64%higher than NC+4Gy group. Autophagy rate in mimic+4Gy group was7.67%higher than mimicgroup(p<0.05). The result suggested that overexpression of miR-18a could enhanceIR induced autophagy in SW116cells.3. miR-18a regulate the expression ofATM in two colorectal cancer cells(1).miR-18a upregulatedATM expression level in SW480cellsWestern Blot showed that ATM expression level was a slightly higher in mimicgroup than in NC group, and ATM expression level was higher in mimic+4Gy groupthan in NC+4Gy group. The result indicated that miR-18a up-regulated ATMexpression level in SW480cells.(2).miR-18a downregulatedATM expression level in SW116cellsWestern Blot showed that ATM expression level was lower in mimic group thanin NC group,and ATM expression level was lower in mimic+4Gy group than inNC+4Gy group. The result indicated that miR-18a down-regulated ATM expressionlevel in SW116cells.Conclusion:1.Overexpression of miR-18a decreases sensitivity to IR and G2/M phase arrestin SW480cells, but increases sensitivity to IR and G2/M phase arrest in SW116cells.2.miR-18a plays different roles in autophagy between SW480cells and SW116cells. miR-18a suppresses IR induced autophagy in SW480cells. In the converse,miR-18a enhances IR induced autophagy in SW116cells.3. miR-18a suppresses IR induced apoptosis in SW480cells. 4. miR-18a up-regulates ATM expression level in SW480cells. In the converse,miR-18a down-regulates ATM expression level in SW116cells.