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- Title
Epigenetic Inactivation of <i>Inositol polyphosphate 4-phosphatase B</i> (<i>INPP4B</i>), a Regulator of PI3K/AKT Signaling Pathway in EBV-Associated Nasopharyngeal Carcinoma.
- Authors
Yuen, Jessie Wai-Fong; Chung, Grace Tin-Yun; Lun, Samantha Wei-Man; Cheung, Chartia Ching-Mei; To, Ka-Fai; Lo, Kwok-Wai
- Abstract
Nasopharyngeal carcinoma (NPC) is a common viral-associated neoplasm in which multiple signaling cascades are interfered with by Epstein-Bar virus (EBV) latent proteins and various genetic alterations. Aside from the previously reported PIK3CA amplification, we examined the role of INPP4B, a negative regulator of the PI3K/AKT signaling pathway in the development of NPC. By RT-PCR and Western blotting, we revealed that the expression of INPP4B was down-regulated in all five established EBV-positive tumor lines. While INPP4B was consistently expressed in normal nasopharyngeal epithelial cells, downregulation of INPP4B was found in 32/65 (49.2%) of primary tumors by immunohistochemistry. Furthermore, our study also demonstrated the hypermethylation of the 5′CpG island of INPP4B in the tumors in which INPP4B transcription was downregulated. Notably, the re-expression of INPP4B was detected in the NPC cells treated with the demethylation agent (5-aza-2′deoxycytidine). Our study showed that promoter hypermethylation was the major mechanism for transcriptional silencing of INPP4B in NPC. Furthermore, restoration of INPP4B expression significantly suppressed PI3K/AKT downstream signals in the NPC C666-1 cells. In vivo growth inhibition was clearly demonstrated in the tumor cells stably expressing INPP4B. The findings indicate that epigenetic inactivation of INPP4B is one of the key mechanisms in activating PI3K/AKT signaling cascade and playing a role in the tumorigenesis of NPC.
- Subjects
EPIGENETICS; GENE silencing; POLYPHOSPHATES; GENETIC regulation; PHARYNGEAL cancer; CELLULAR signal transduction; DIAGNOSIS
- Publication
PLoS ONE, 2014, Vol 9, Issue 8, p1
- ISSN
1932-6203
- Publication type
Article
- DOI
10.1371/journal.pone.0105163