Extra-nuclear estrogen signaling

E2-evoked extra-nuclear signaling is independent of the transcriptional activity of estrogen receptors and occurs within seconds to minutes following E2 administration to target cells. Extra-nuclear signaling consists of the activation of a plethora of signaling pathways including the RAF/MAP kinase cascade and the PI3K/AKT signaling cascade and governs processes such as apoptosis, cellular proliferation and metastasis (reviewed in Hammes et al, 2007; Handa et al, 2012; Lange et al, 2007; Losel et al, 2003; Arnal et al, 2017; Le Romancer et al, 2011). ESR-mediated signaling also cross-talks with receptor tyrosine kinase, NF- kappa beta and GPCR signaling pathways by modulating the post-translational modification of enzymes and other proteins and regulating second messengers (reviewed in Arnal et al, 2017; Schwartz et al, 2016; Boonyaratanakornkit, 2011; Biswas et al, 2005). In the nervous system, E2 affects neural functions such as cognition, behaviour, stress responses and reproduction in part by inducing such rapid extra-nuclear responses, while in endothelial cells, non-genomic ESR-dependent signaling also regulates vasodilation through the eNOS pathway (reviewed in Levin, 2011).

Extra-nuclear signaling additionally cross-talks with nuclear estrogen receptor signaling and is required to control ER protein stability (La Rosa et al, 2012)

Recent data have demonstrated that the membrane ESR1 can interact with various endocytic proteins to traffic and signal within the cytoplasm. This receptor intracellular trafficking appears to be dependent on the phyical interaction of ESR1 with specific trans-membrane receptors such as IGR-1R and beta 1-integrin