Proline-, glutamic acid-, and leucine-rich protein-1 (PELP1) (also known as modulator of non-genomic activity of estrogen receptor, or MNAR) is a novel estrogen receptor (ER) co-regulator. PELP1 modulates ER genomic, as well as non-genomic, functions and its expression is deregulated in a number of tumors. To understand the biological functions of PELP1, we sought to identify its binding partners using yeast two-hybrid screen. In this study, we identified the four and a half LIM-only protein 2 (FHL2) as a novel interacting protein of PELP1 and found evidence of physiological interaction between PELP1 and FHL2. In Gal4-FHL2 reporter assays, PELP1 enhanced the transcriptional activity of FHL2, indicating a direct functional interaction between PELP1 and FHL2. Utilizing co-immunoprecipitation and protein pull-down assays, we mapped the N-terminal region of PELP1 (aa 1- 400) as the FHL2 interacting region. Deletion studies revealed that the third and fourth LIM domains of FHL2 were required for interaction with PELP1. In prostate-specific antigen (PSA) and MMTV promoter-driven luciferase assays, PELP1 enhanced FHL2 mediated Androgen Receptor (AR) transactivation functions. Biochemical and confocal analysis revealed complex formation among PELP1, AR, FHL2, and predominant interaction of PELP1with FHL2 was observed in the nuclear compartment. PELP1 mutant, which lacks a specific chromatin-interacting motif, failed to promote FHL2 transactivation functions. PELP1 is widely expressed in epithelial prostate cancer cell lines. Immunohistological staining of prostate tumors (tissue array n=30) showed increased expression of PELP1 with tumor grade. Our results suggest that ER co-activator PELP1 plays a role in AR transactivation functions through PELP1-FHL2 interactions, and may have role in prostate cancer progression.

[Proc Amer Assoc Cancer Res, Volume 46, 2005]