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Open Access Research article

Knocking down CDK4 mediates the elevation of let-7c suppressing cell growth in nasopharyngeal carcinoma

Zhen Liu12, Xiaobin Long245, Cheng Chao245, Chen Yan2, Qiangyun Wu2, Shengni Hua2, Yajie Zhang12*, Aibing Wu23* and Weiyi Fang26*

Author Affiliations

1 Department of Pathology, Guangzhou Medical University, Guangzhou 510182, China

2 Cancer Research Institute, Southern Medical University, Guangzhou 510515, China

3 Cancer Center of Affiliated Hospital, Guangdong Medical College, Zhanjiang 524001 PR, China

4 Otorhinolaryngology of Zhujiang Hospital, Southern Medical University, Guangzhou 510282 PR, China

5 Pediatric Center of Zhujiang Hospital, Southern Medical University, Guangzhou 510282 PR, China

6 Tumor Center of Integrated Chinese and Western medicine Hospital, Southern Medical University, Guangzhou 510315 PR, China

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BMC Cancer 2014, 14:274  doi:10.1186/1471-2407-14-274

Published: 21 April 2014

Abstract

Background

CDK4 is a protein kinase in the CDK family important for G1/S phase cell cycle progression. However, the roles and molecular mechanisms of CDK4 triggering nasopharynx carcinogenesis are still unclear.

Methods

Lentiviral-vector mediated shRNA was used to suppress CDK4 expression and examine its molecular mechanisms. Using immunohistochemistry, we analyzed CDK4 protein expression in clinicopathologically characterized nasopharyngeal carcinoma (NPC) cases and nasopharyngeal tissues (NPs). Survival curves were plotted by the Kaplan-Meier method and compared using the log-rank test.

Results

In this investigation, we knocked down CDK4 expression and observed that NPC cell growth and cell cycle progression were significantly blocked by suppressing expression of CCND1, CDK6, and E2F1 as well as elevated p21 expression. Further, we found that reduced CDK4 expression elevated the expression of let-7c, a tumor-suppressive miRNA modulated by E2F1. We found that let-7c was markedly downregulated in NPC tissues compared to NPs and suppressed cell growth and cell cycle progression by modulating p15/p16/CDK4/E2F1 pathway. Finally, CDK4 protein was observed to be overexpressed in NPC tissues and could be considered an unfavorable prognosis factor for NPC patients although its independent prognostic value did not reach statistical significance (pā€‰=ā€‰0.087).

Conclusions

Our results demonstrated that overexpressed CDK4 is an unfavorable prognostic factor which suppresses the expression of tumor suppressive-factor let-7c through p21/CCND1/CDK6/E2F1 signaling, and inhibits cell proliferation by p15/p16/CDK4/E2F1 feedback signaling in NPC.

Keywords:
NPC; CDK4; let-7c; Prognosis