miR-18a inhibits CDC42 and plays a tumour suppressor role in colorectal cancer cells.
The miR-17-92 cluster of microRNAs is elevated in colorectal cancer, and has a causative role in cancer development. Of the six miR-17-92 cluster members, miR-19a and b in particular are key promoters of cancer development and cell proliferation, while preliminary evidence suggests that miR-18a may act in opposition to other cluster members to decrease cell proliferation. It was hypothesised that miR-18a may have a homeostatic function in helping to contain the oncogenic effect of the entire miR-17-92 cluster, and that elevated miR-17-92 cluster activity without a corresponding increase in miR-18a may promote colorectal tumour progression. In colorectal cancer samples and corresponding normal colorectal mucosa, miR-18a displayed lower overall expression than other miR-17-92 cluster members. miR-18a was shown to have an opposing role to other miR-17-92 cluster members, in particular the key oncogenic miRNAs, miR-19a and b. Transfection of HCT116 and LIM1215 colorectal cancer cell lines with miR-18a mimics decreased proliferation, while a miR-18a inhibitor increased proliferation. miR-18a was also responsible for decreasing cell migration, altering cell morphology, inducing G1/S phase cell cycle arrest, increasing apoptosis, and enhancing the action of a pro-apoptotic agent. CDC42, a mediator of the PI3K pathway, was identified as a novel miR-18a target. Overexpression of miR-18a reduced CDC42 expression, and a luciferase assay confirmed that miR-18a directly targets the 3'UTR of CDC42. miR-18a mimics had a similar effect on proliferation as a small molecule inhibitor of CDC42. Inhibition of CDC42 expression is likely to be a key mechanism by which miR-18a impairs cancer cell growth, with a target protector experiment revealing miR-18a influences proliferation via direct inhibition of CDC42. Inhibition of CCND1 by miR-18a may also assist in this growth-suppression effect. The homeostatic function of miR-18a within the miR-17-92 cluster in colorectal cancer cells may be achieved through suppression of CDC42 and the PI3K pathway.
Flinders Centre for Innovation in Cancer, School of Medicine, Flinders University, Flinders Medical Centre, Adelaide, South Australia, Australia.
Karen J
KJ
Humphreys
Flinders Centre for Innovation in Cancer, School of Medicine, Flinders University, Flinders Medical Centre, Adelaide, South Australia, Australia.
Ross A
RA
McKinnon
Flinders Centre for Innovation in Cancer, School of Medicine, Flinders University, Flinders Medical Centre, Adelaide, South Australia, Australia.
Michael Z
MZ
Michael
D020413:3' Untranslated Regions; D045744:Cell Line, Tumor; D049109:Cell Proliferation; D003106:Colon / Q000473:pathology*; D015179:Colorectal Neoplasms / Q000235:genetics* / Q000473:pathology*; D015972:Gene Expression Regulation, Neoplastic; D006801:Humans; D035683:MicroRNAs / Q000235:genetics*; D012007:Rectum / Q000378:metabolism / Q000473:pathology*; D020764:cdc42 GTP-Binding Protein / Q000235:genetics*
D020413:3' Untranslated Regions; C522576:MIRN18A microRNA, human; D035683:MicroRNAs; D020764:cdc42 GTP-Binding Protein