PELP1--a novel estrogen receptor-interacting protein

Abstract

PELP1 (proline-, glutamic acid-, and leucine-rich protein-1) is a novel estrogen receptor (ER)-interacting protein that has been implicated to be important for mediation of both the genomic and nongenomic signaling of 17beta-estradiol (E2). PELP1 contains ten nuclear receptor-interacting boxes (LXXLL motifs), which allow it to interact with ER and other nuclear hormone receptors, a zinc finger, a glutamic acid-rich domain, and two proline-rich domains. The proline-rich regions contain several consensus PXXP motifs, which allow PELP1 to couple the ER with SH3 domain-containing kinase signaling proteins, such as Src and PI3K P85 regulatory subunit. PELP1 is expressed in many different brain regions, including the hippocampus, hypothalamus, and cerebral cortex. Further work has demonstrated that PELP1 is colocalized with ER-alpha in neurons in various brain regions. PELP1 is primarily expressed in neurons, with some expression also observed in glia. Subcellular localization studies revealed that PELP1 is highly localized in the cell nucleus of neurons, with some cytoplasm localization as well, and PELP1 is also localized at synaptic sites. Work in other tissues has demonstrated that PELP1 is critical for nongenomic and genomic signaling by E2, as PELP1 knockdown studies significantly attenuates E2-induced activation of ERK and Akt signaling pathways, and inhibits E2 genomic transcriptional effects on gene expression in breast cancer cells. Preliminary studies in the brain, suggests that similar roles may exist for PELP1 in the brain, but this remains to be established, and further work to characterize the precise roles and functions of PELP1 in the brain are needed.

Figure 1. Schematic diagram of PELP1/MNAR interacting proteins and functional domains

PXXP, SH3, Src homology3 binding domain; LXXLL, nuclear receptor interacting domain; glu rich, histone binding domain; NLS, nuclear localization signal. Putative PELP1 phosphorylation sites (Ser, serine, Thr, theronine; Tyr, tyrosine) are indicated. Known PELP1 interacting proteins are shown and are grouped based on putative non genomic and genomic functions.

Figure 2. Preliminary co-immunoprecipitation analysis of PELP1-ER-Src and PELP1-ERPI3K- p85 complex in rat hippocampal CA1 from placebo- and 17β-estradiol (E2)-treated ovariectomized rats following 4-vessel global cerebral ischemia

Sample proteins from placebo and E2-treated ovariectomized female rats were collected 30 min after cerebral ischemia, and were separately immunoprecipitated (IP) using antibody against ERα, PELP1 and Src, and then Western blot (WB) performed with indicated antibodies. At the time of ovariectomy, placebo or 17β-estradiol (E2) time-release pellets (0.025mg; 21 day release pellet) were implanted subcutaneously in the upper mid-back region under the skin. The E2 pellets produce diestrus 1 level serum E2 levels (~10 pg/ml), which strongly protects the hippocampus CA1 from cerebral ischemia-induced neuronal cell death. Note that E2 strongly up-regulates PELP1-ER-Src and PELP1-ER-PI3K-p85 complex formation as compared to placebo control.

Figure 3. Subcellular localization of PELP1 in the rat brain

A Low-magnification view of silver-enhanced nanogold labeling of the PELP1 localization in the CA1 pyramidal cell layer of the hippocampus. B Electron micrograph of an individual pyramidal cell from the CA1 area showing nuclear and cytoplasmic compartments as well as various cytoplasmic organelles. C , D High-resolution electron micrographs showing PELP1-positive gold particles localized in nucleus and cytoplasm, respectively. E–H High-resolution electron micrographs showing localization of PELP1-positive gold particles in the dendritic shafts and pre- and postsynaptic terminals. Ds = Dendritic shafts; PSDs = postsynaptic density complexes; PSD = presynaptic dendritic vesicles; Ps = presynaptic vesicles. I Localization of PELP1 in an astrocyte. Scale bars represent 50 nm in A and 200 nm in B–I . With permission from Khan et. al. 2006.