Androgen regulation of the largest subunit of RNA polymerase II in the rat ventral prostate

ELL binding regulates U19/Eaf2 intracellular localization, stability, and transactivation

BACKGROUND

U19/Eaf2, an androgen-response gene, is downregulated in advanced human prostate cancer specimens and its overexpression can markedly induce apoptosis in prostate cancer cells. Eleven-nineteen Lysine-rich Leukemia (ELL) is an RNA polymerase II transcription elongation factor, initially identified as a fusion partner gene of MLL in the t(11; 19) (q23; p13.1) chromosomal translocation in acute myeloid leukemia. U19/Eaf2 was previously reported as an ELL-associated factor, a potential transcription factor binds to ELL, forming nuclear speckles in vivo. These findings suggest that ELL-U19/Eaf2 interaction is potentially important in prostate cancer progression and/or acute myeloid leukemia. However, the functional significance of U19/Eaf2 interaction with ELL remains unclear.

METHODS

Using co-transfection, co-immunoprecipitation, protein stability assay and transactivation assay, we characterized the consequence of ELL binding to U19/Eaf2.

RESULTS

We provide further evidence for U19/Eaf2 as a transcription factor and show that ELL binding is required for nuclear speckle formation of human U19/Eaf2, stabilizes U19/Eaf2 and enhances its transactivation activity.

CONCLUSIONS

The above observations indicate ELL may be an important factor required for U19/Eaf2 function because U19/Eaf2 nuclear localization and transactivation activity are essential for its function as a transcription factor.

Identification and characterization of PLZF as a prostatic androgen-responsive gene

BACKGROUND

Promyelocytic leukemia zinc finger protein (PLZF) was initially identified by virtue of its fusion with RARalpha as a result of a variant t(11;17) chromosomal translocation that occurs in a small subset of acute promyelocytic leukemia (APL) patients. PLZF has been reported to have pro-apoptotic and anti-proliferative activity both in vivo and in vitro.

METHODS

Using a modified subtractive hybridization, we identified PLZF as an androgen-responsive gene in the rat ventral prostate. Northern blot and Western blot were used to characterize the regulation of PLZF by androgens in LNCaP cells. Stable transfections of PLZF in LNCaP cells were performed to assay the effect of PLZF overexpression on LNCaP cell proliferation.

RESULTS

PLZF mRNA was transiently up-regulated by androgens in the regressed ventral prostate of castrated adult rat. PLZF was also up-regulated by androgens, at both mRNA and protein levels, in the androgen-responsive human prostate cancer cell line LNCaP. Androgen induction of PLZF mRNA was not inhibited by protein synthesis inhibitor cycloheximide but inhibited by androgen receptor antagonist bicalutamide, indicating that PLZF is a direct androgen-responsive gene. To study the functions of PLZF in androgen action, LNCaP sublines stably overexpressing PLZF were generated. PLZF overexpression inhibited LNCaP proliferation either in the presence or absence of androgen, which is consistent with the reported anti-proliferative activity of PLZF.

CONCLUSIONS

The above observations indicate that PLZF is an androgen-responsive gene with anti-proliferative activity in prostate cancer cells.