IncRNA PLAC2 Upregulates CDK6 by Directly Targeting miR-29C to Promote Cell Proliferation in Lung Squamous Cell Carcinoma.

Long noncoding RN (IncRNA) placenta-specific 2 (PLAC2) plays a critical role in many cancer types. A previous study found that PLAC2 expression dysregulated in non-small cell lung cancer (NSCLC). However, its function in LSCC is not entirely known. The present study enrolled 68 lung squamous cell carcinoma (LSCC, a major subtype of NSCLC) patients (gender: 39 males and 29 females; age: 36 to 67 years old; mean age: 53.2 ± 5.5 years old). The expression levels of PLAC2 in two types of tissue (non-tumor and LSCC) were measured by quantitative PCR. LSCC cells H1581 and H1993 were transfected with PLAC2 and cyclin-dependent kinase 6 (CDK6) expression vectors and small interfering RNAs (siRNAs), as well as microRNA-29C (miR-29C) mimic and inhibitor to perform overexpression and knock-down experiment, respectively. PLAC2 was upregulated in LSCC and positively correlated with CDK6 but negatively correlated with miR-29C. During a 5-year follow-up, high expression levels of PLAC2 were found to be closely associated with poor survival. PLAC2 and CDK6 were significantly upregulated in LSCC cells, while miR-29C was remarkably downregulated. miR-29C was predicted to be a potential target of PLAC2, and RNA pull-down assay confirmed their direct interaction. Overexpression of PLAC2 led to upregulation of CDK6 and downregulation of miR-29C, while knock-down of PLAC2 showed opposite effects. Overexpression of miR-29C downregulated CDK6, while knock-down of miR-29C increased the expression levels of CDK6. However, the expression of PLAC2 was not affected by overexpression or knock-down of miR-29C. Overexpression of PLAC2 and CDK6 enhanced LSCC cell proliferation and cell cycle progression, while knock-down showed opposite effects. In addition, overexpression of miR-29C inhibited cell proliferation and cell cycle progression, while its knockdown display opposite effects. Moreover, overexpression of miR-29C suppressed the role of overexpression of PLAC2 in cell proliferation and cell cycle progression. In conclusion, PLAC2 upregulates CDK6 by downregulating miR-29C to promote LSCC cell proliferation.