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The RNA‐binding and adaptor protein Sam68 modulates signal‐dependent splicing and transcriptional activity of the androgen receptor
Author(s) -
Rajan P,
Gaughan L,
Dalgliesh C,
ElSherif A,
Robson CN,
Leung HY,
Elliott DJ
Publication year - 2008
Publication title -
the journal of pathology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.964
H-Index - 184
eISSN - 1096-9896
pISSN - 0022-3417
DOI - 10.1002/path.2324
Subject(s) - androgen receptor , lncap , rna splicing , biology , exon , alternative splicing , rna binding protein , ectopic expression , cancer research , microbiology and biotechnology , prostate cancer , rna , gene , genetics , cancer
The RNA‐binding protein Sam68 has been reported to be up‐regulated in clinical cases of prostate cancer (PCa), where it is thought to contribute to cell proliferation and survival. Consistent with this, we observed over‐expression of Sam68 in a panel of clinical prostate tumours as compared with benign controls. Since Sam68 is implicated in a number of signalling pathways, we reasoned that its role in PCa may involve modulation of the androgen receptor (AR) signalling cascade, which drives the onset and progression of PCa. We found that Sam68 interacts with the AR in vivo in LNCaP cells, and is dynamically recruited to androgen response elements within the promoter region of the prostate‐specific antigen ( PSA ) gene. Based on its known functions and nuclear location, Sam68 might either: (a) co‐regulate AR‐dependent transcription positively or negatively; or (b) modulate AR‐dependent alternative splicing by enhancing incorporation of a Sam68‐responsive exon transcribed under the control of an androgen‐responsive promoter. We tested these possibilities using functional assays. Both wild‐type Sam68 protein and the Sam68 V229F mutant, which is impaired in RNA binding, functioned as a ligand‐dependent AR co‐activator on an androgen‐regulated reporter gene. In contrast, splicing of a Sam68‐responsive variable exon, transcribed under control of an androgen‐responsive promoter, was strongly repressed in the presence of AR and androgens. This splicing inhibition was reversed by ectopic expression of Sam68 but enhanced by Sam68 V229F . These results demonstrate that Sam68 has separable effects on AR‐regulated transcriptional activity and alternative splicing, both of which may affect PCa phenotypes. Copyright © 2008 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.