Role of multi-hnRNP nuclear complex in regulation of tumor suppressor ANXA7 in prostate cancer cells.

Annexin-A7 (ANXA7) tumor suppressor role has been shown in various tumors, and ANXA7 expression has been particularly lost in androgen-resistant prostate cancers. In this study, we studied ANXA7 regulation in normal prostate versus androgen-sensitive and -resistant prostate cancer cells. Deletion mapping analysis showed lowest ANXA7-promoter activities in androgen-sensitive LNCaP prostate cancer cells. Genomatix analysis of ANXA7 promoter identified a cluster of steroid nuclear hormone receptor elements, including V$GREF (V$GRE.02/ARE.02). Gelshift analysis clearly indicated distinct nuclear protein occupancy at this ANXA7-promoter site (-1086/-890) in prostate cancer (LNCaP, DU145, and PC3) versus normal prostate (PrEC) cells. In matrix-assisted laser desorption time-of-flight mass spectrometry-based search for ANXA7 nuclear regulators, we identified several heterogeneous nuclear ribonucleoproteins (hnRNPs) (A1, A2/B1 and K) attached to the steroid-associated ANXA7-promoter site in the androgen-resistant PC3 prostate cancer cells with high ANXA7 gene copy number, but not in PrEC. The hnPNP role in ANXA7 regulation (that was validated by hnRNPA2/B1 antibody interference) resulted in multiple ANXA7 cDNA and protein products in PC3, but not in PrEC. Ingenuity pathways analysis showed plausible molecular paths between ANXA7 and the hnRNP-associated network in prostate cancer progression. Thus, a multi-hnRNP complex can be responsible for aberrant ANXA7 transcription and splicing, thereby affecting ANXA7 expression pattern and tumor suppressor function in prostate cancer.