Abstract
Estrogen receptor α (ERα) functions as a ligand dependent transcription factor that directly binds specific estrogen responsive elements, thus regulating the transcription of estrogen sensitive genes. ERα has also been shown to be associated with the plasma membrane (membrane associated ERα, mERα), concentrated in lipid rafts, plasma membrane microdomains with a distinct lipid composition, where it transduces membrane-initiated estrogen-dependent activation of the mitogen-activated protein (MAP) kinase signaling pathway. Two isoforms of ERα have been described: the “traditional” ERα66 (66 kDa) and a lower molecular weight variant: the ERα46 (46 kDa). More recently, a novel ERα variant with a molecular mass of 36 kDa (ERα36) has been discovered. Notably, ERα36 has been found expressed in different human tumor cells, including both ER- positive and ER- negative breast cancer cells. Estrogen signaling at the cell membrane via ERα36 appears as capable of activating multiple pathways of importance for cancer aggressiveness and metastatic potential. The presence of serum autoantibodies reacting with mERα (anti-ERα Abs) in a large percentage of patients with breast cancer has recently been reported by our group. These anti-ERα Abs seem to act as estrogen agonists rapidly triggering MAP kinase pathway activation thus inducing tumor cell proliferation and overcoming cell resistance to anti-estrogen drug tamoxifen. In this review, we describe the involvement of ERα36 in different tumors. We also report the potential pathogenetic activity of anti-ERα Abs and their implication in drug resistance.
Highlights
The biological effects of estrogen are mediated by specific receptors designated as estrogen receptors (ERs) [1]
A positive correlation between ERα36 and epidermal growth factor receptor (EGFR) expression levels has been observed in Hec1A cultured cells suggesting the involvement of ERα36 in the activation of the extracellular signaling linked to EGFR in endometrial carcinoma [45]
Summarazing, it can be hypothesized that ERα36 could play an important role in estrogen signaling during the development and progression of several forms of cancer
Summary
The biological effects of estrogen are mediated by specific receptors designated as estrogen receptors (ERs) [1]. The ERβ is 530 amino acids in length, with a molecular weight of 59 kDa and it is encoded by the gene estrogen receptor 2 (ESR2), located on chromosome 14, locus 14q23.2 [14]. This unique amino acid sequence in ER36 may alter the ligand binding domain, which explains why ER36 has a different binding affinity This receptor is mainly located in cytoplasm and at the plasma membrane of several different cancer cell types [19,20,21] and even in healthy tissues, among which ovarian, breast, kidney, lung, heart and bone [22]. Whether ERα36 could play a role in other human cancers is still scarcely investigated and cannot be ruled out
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