Pathological Significance and Therapeutic Implications of ER Non-Genomic Actions.
Authors: Chakravarty D. , Nair S. , Cortez V. , Dandamudi R. , Challa R. , Tekmal R. , Kumar R. , Vadlamudi R. , Lee F. 
Published: December 2010

Background: Emerging evidence suggests that in addition to genomic functions, estrogen receptor (ER) participates in extra-nuclear rapid signaling, commonly termed as nongenomic signaling, via the formation of signaling complexes in the cytoplasm. Although much is known about ER genomic actions, the mechanism and pathobiology of ER-nongenomic actions remains poorly understood. Proline glutamic acid rich protein 1(PELP1), an established ER coregulator that participates both in ER-genomic and nongenomic actions. Recent findings implicate PELP1 as a novel proto-oncogene and its expression correlates well with a poor prognosis and therapeutic resistance. In the present study, we examined pathological significance of ER-PELP1 nongenomic signaling in the development of mammary tumorigenesis.Methods: To evaluate the role of ER-PELP1 nongenomic signaling in tumorigenesis and therapeutic resistance, we have generated the following breast cancer model cells with functional or defective ER-PELP1-Src axis: (1) MCF-7 cells; (2) MCF-7 HER2 that overexpress HER2; (3) MCF7-Tam that acquired resistance to tamoxifen and (4) MCF-7Ca-LTLT that acquired resistance to Letrozole. These model cells were searched for evidence of functional nongenomic signaling using phosphospecific antibodies, and for hormonal responsiveness in the proliferation assays. To establish the physiologic significance of ER-nongenomic action, we have used xenograft- and transgenic-mice (TG) models that express ER coregulator PELP1 in the cytoplasm (PELP1cyto). Combinatorial therapy of endocrine agents along with drugs that block nongenomic signaling including Src inhibitor (Dasatinib, BMS-354825) were tested in various biologic assays.Results: Mechanistic studies using PELP1- or Src-defective models revealed that knockdown of either PELP1 or Src kinase abolishes ER-nongenomic signaling. Pharmacological inhibition of the Src kinase using Dasatinib significantly inhibited activation ER non-genomic actions. Dasatinib also inhibited the tumorigenic potential of breast cancer cells with PELP1 overexpression in xenograft studies, as well as sensitized resistant model cells to hormonal therapy. Cytoplasmic expression of PELP1 promoted excessive activation of Src kinase in the mammary gland of PELP cyto Tg mice. Aging of the PELP1cyto Tg mice (n=60) for 24 months revealed the presence of an excessive activation of ER-nongenomic signaling in the mammary gland, and promoted hyperplasia at the age of 10 weeks with formation of mammary carcinomas beginning at ∼12 months of age. These results suggest that ER-nongenomic signaling has the potential to promote formation of ER-positive mammary carcinomas.Conclusions: Our results suggest that non-genomic signaling components have potential to promote ER-positive breast tumorigenesis and confer therapeutic resistance. Our findings suggest that ER-PELP1-Src axis represents a novel target for blocking ER-nongenomic actions. As ER genomic and nongenomic signaling are involved in tumorigenesis and resistance, combination therapies using tamoxifen or letrozole with Dasatinib that block different pathways may have a better therapeutic efficacy and could delay the on-set of hormonal resistant in the advanced breast tumors.This research was supported by grants CA0095681 and W81XWH-08-1-0604.

Citation Information: Cancer Res 2009;69(24 Suppl):Abstract nr 3127.