Pirin down‐regulates the EAF 2/ U 19 protein and alleviates its growth inhibition in prostate cancer cells

BACKGROUND The tumor suppressor ELL associated factor 2 (EAF2/U19) has been reported to induce apoptosis of LNCaP cells and suppress AT6.1 xenograft prostate tumor growth. EAF2/U19 expression level is down‐regulated in advanced human prostate cancer. EAF2/U19 is also a putative transcription factor with a transactivation domain and capability of sequence‐specific DNA binding. Identification of binding partners and regulators of EAF2/U19 is essential to understand its function in regulating apoptosis/survival of prostate cancer cells. METHODS Through a yeast two‐hybrid screening system, we identified Pirin as a binding partner of EAF2. We further determined the interaction between epitope‐tagged EAF2/U19 and Pirin by co‐immunoprecipitation in mammalian cells. The effect of Pirin on EAF2/U19 inhibition of LNCaP growth was assayed by colony formation. RESULTS Pirin co‐immunoprecipitated with EAF2/U19 and the overexpressed Pirin decreased the expression level of EAF2/U19 protein in prostate cancer cell lines LNCaP and PC3. Furthermore, overexpression of EAF2/U19 suppressed LNCaP colony formation, and co‐expression of Pirin significantly blocked the growth inhibition induced by EAF2/U19 overexpression. CONCLUSION Pirin is a newly identified binding partner of EAF2/U19 capable of down‐regulating EAF2/U19 protein and alleviating its inhibition of prostate cancer cell survival/proliferation. Pirin may play an important role involved in EAF2/U19 function as an androgen‐responsive gene and tumor repressor. Prostate 74:113–120, 2014 . © 2013 Wiley Periodicals, Inc.