Abstract: Objective:To investigate microRNA- 29c (miR-29c) expression and its relationship with CDC 42in gliomas, as well as to observe its effects on the proliferation of the U 87MG glioma cell line. Methods:The expression levels of miR-29c and CDC 42 were determined by using locked-oligonucleotide-probein situ hybridization and immunohistochemistry in 10cases with nontumor control brain tissues and 60patients with gliomas of 4 pathological grades. Mature mimics of miR-29c and scrambled sequences were chemically synthesized and then transiently transfected into the U 87MG glioma cell line. The miR-29c expression level was quantified by using stem-loop real-time quantitative reverse transcription-polymerase chain reaction (qRT-PCR). The expression levels of CDC 42 mRNA and protein, as well as the proliferation capabilities of U 87MG, were evaluated by qRT-PCR, Western blot, and MTS assay. Results:Locked-oligonucleotide-probeinsitu hybridization showed a downregulation of miR-29c in all glioma samples compared with subjects having nontumor control brain tissues; a continuous decrease was observed as the malignant grade of the tumors increased ( P<0.001). CDC 42immunohistochemistry exhibited the opposite pattern. The Labeling index (LI%) value of CDC 42was the highest in the WHO grade IV group. All between-group differences, except for that between the WHO grade I-II and nontumor control groups, were statistically significant ( P<0.001). The miR- 29c expression levels in miR-29c transcription groups were significantly higher than those in the blank and Scr control groups ( P<0.001). Compared with the values for the control groups, the CDC 42mRNA (P<0.001) and protein (P<0.01) levels were significantly decreased in the miR- 29c transcription groups. The proliferation capabilities of the U 87MG glioma cell line in miR- 29c transcription groups were significantly lower than those of the control groups at 48(P<0.05), 72(P<0.05), and 96h (P<0.001) after transient miR- 29c transfection. Conclusion:miR-29c is an important tumor-suppressive miRNA that could be used as an important marker to assess the malignant degree of gliomas. The aberrant decrease in miR- 29c expression in gliomas resulted in CDC 42 upregulation and facilitated glioma cell immortalization. These findings further confirm that miR-29c downregulation may be a key mechanism for glioblastoma tumorigenesis.