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Splice variants of the forkhead box protein AFX exhibit dominant negative activity and inhibit AFXalpha-mediated tumor cell apoptosis.

Authors
 Eun Jig Lee  ;  Jeong Mo Kim  ;  Mi Kyung Lee  ;  J. Larry Jameson 
Citation
 PLOS ONE, Vol.3(7) : e2743, 2008 
Journal Title
 PLOS ONE 
Issue Date
2008
MeSH
Alternative Splicing* ; Apoptosis* ; Cell Line, Tumor ; Cell Nucleus/metabolism ; Cyclin D2 ; Cyclins/metabolism ; Cytoplasm/metabolism ; DNA-Binding Proteins/metabolism ; Forkhead Transcription Factors/metabolism* ; Genes, Dominant ; Genes, Tumor Suppressor ; HeLa Cells ; Humans ; Neoplasms/metabolism* ; Protein Isoforms ; Proto-Oncogene Proteins c-bcl-6 ; Transcription Factors/metabolism*
Keywords
Alternative Splicing* ; Apoptosis* ; Cell Line, Tumor ; Cell Nucleus/metabolism ; Cyclin D2 ; Cyclins/metabolism ; Cytoplasm/metabolism ; DNA-Binding Proteins/metabolism ; Forkhead Transcription Factors/metabolism* ; Genes, Dominant ; Genes, Tumor Suppressor ; HeLa Cells ; Humans ; Neoplasms/metabolism* ; Protein Isoforms ; Proto-Oncogene Proteins c-bcl-6 ; Transcription Factors/metabolism*
Abstract
BACKGROUND: Loss-of-function in the apoptosis-inducing genes is known to facilitate tumorigenesis. AFX (FOXO4), a member of forkhead transcription factors functions as a tumor suppressor and has 2 isoforms, AFXalpha (505 a.a.) and AFXzeta (450 a.a.). In human cancer cells, we identified an N-terminally deleted form of AFXalpha (alpha198-505), translated from a downstream start and 2 short N-terminal AFX proteins (90, and 101 a.a.) produced by aberrant splicing. METHODS AND FINDINGS: We investigated the expression and role of these AFX variants. Cell transduction study revealed that short N-terminal AFX proteins were not stable. Though alpha(198-505) protein expression was detected in the cytoplasm and nucleus, alpha(198-505) expressing cells did not show a nucleocytoplasmic shuttling mediated by PI3 kinase signaling. Whereas, we observed this shuttling in cells expressing either AFXalpha or AFXzeta protein. AFXzeta and alpha(198-505) lost the ability to transactivate BCL6 or suppress cyclin D2 gene expression. These variants did not induce cancer cell death whereas AFXalpha resulted in apoptosis. We found that AFXzeta and alpha(198-505) suppress the AFXalpha stimulation of BCL6 promoter in a dose dependent manner, indicating dominant negative activity. These variants also inhibited AFXalpha induction of apoptosis. CONCLUSIONS: Loss of function by aberrant splicing and the dominant negative activity of AFX variants may provide a mechanism for enhanced survival of neoplastic cells.
Files in This Item:
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DOI
10.1371/journal.pone.0002743
Appears in Collections:
1. College of Medicine (의과대학) > Dept. of Internal Medicine (내과학교실) > 1. Journal Papers
Yonsei Authors
Lee, Eun Jig(이은직) ORCID logo https://orcid.org/0000-0002-9876-8370
URI
https://ir.ymlib.yonsei.ac.kr/handle/22282913/107200
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