Rap2 regulates androgen sensitivity in human prostate cancer cells.
BACKGROUND
Progression of prostate cancer to a fatal androgen-independent disease is associated with activation of MAP kinase, consistent with chronic stimulation of the Ras-signaling pathway. We have previously shown that Ras activation is sufficient to induce androgen-independent growth of prostate cancer cells. One mechanism of MAP kinase regulation is modulation of Ras signaling by other Ras family members, the Rap gene paralogs Rap1a/b and Rap2a/b. Here we ask if Rap proteins play a role in determining androgen sensitivity of human prostate cancer cells either alone or in the context of an activated Ras.


METHODS
To evaluate the role of Rap proteins in androgen responsiveness we use Rap over-expression with or without mutated Ras co-transfection and Rap siRNA knockdown to evaluate androgen-dependent prostate-specific antigen (PSA) promoter reporter expression and cell growth in androgen-dependent LNCaP and independent C4-2 human prostate cancer cells.


RESULTS
Rap1 is equally expressed between LNCaP and C4-2 cells and thus we focused on Rap2 which is minimally expressed in C4-2. Rap2a affects androgen-dependent PSA reporter expression in a dose-dependent manner in LNCaP and C4-2 cells. Low levels of Rap2a enhance PSA reporter expression, whereas higher concentrations inhibit expression. We show that Rap2a antagonizes the enhanced PSA reporter expression conferred by an active RasV12 gene in prostate cancer cells. siRNA knockdown data indicate that Rap2 has a greater effect on androgen-stimulated growth in LNCaP than in C4-2 cells.


CONCLUSIONS
We show that Rap2 is involved in androgen-mediated transcriptional and growth responses of human prostate cancer cells.
Bigler
Dora
D
Department of Molecular Physiology and Biological Physics, University of Virginia Health Sciences Center, Charlottesville, Virginia 22908, USA.
Gioeli
Daniel
D
Conaway
Mark R
MR
Weber
Michael J
MJ
Theodorescu
Dan
D
D000230:Adenocarcinoma / Q000235:genetics* / Q000378:metabolism / Q000473:pathology; D000728:Androgens / Q000494:pharmacology / Q000502:physiology*; D000818:Animals; D045744:Cell Line, Tumor; D020558:GTP Phosphohydrolases / Q000378:metabolism; D015972:Gene Expression Regulation, Neoplastic; D006801:Humans; D008297:Male; D051379:Mice; D017430:Prostate-Specific Antigen; D011471:Prostatic Neoplasms / Q000235:genetics* / Q000378:metabolism / Q000473:pathology; D012334:RNA, Neoplasm / Q000032:analysis; D034741:RNA, Small Interfering / Q000494:pharmacology; D000089804:Shelterin Complex; D015398:Signal Transduction; D034501:Telomere-Binding Proteins / Q000235:genetics / Q000378:metabolism; D020668:rap GTP-Binding Proteins / Q000235:genetics* / Q000378:metabolism
D000728:Androgens; D012334:RNA, Neoplasm; D034741:RNA, Small Interfering; D000089804:Shelterin Complex; C440809:TERF2IP protein, human; D034501:Telomere-Binding Proteins; D017430:Prostate-Specific Antigen; D020558:GTP Phosphohydrolases; C116756:RAP2A protein, human; D020668:rap GTP-Binding Proteins