Uces receptor-mediated TAM resistance and transcriptional activity in ER+ breast cancer cells. We propose that ERK-mediated phosphorylation of ERR is a key determinant of TAM resistance in ER+ breast cancer cells where this receptor is expressed and drives the resistant phenotype. To our know-how this is the first demonstration of direct, functional consequences of phospho-regulation of a member in the ERR household. Ariazi et al. initially showed that ERR transcriptional activity in ER+ breast cancer cells is enhanced by HER2 endogenous amplification (BT474) or exogenous expression (MCF7), and that pharmacological inhibition of AKT or MAPK reduces this activity . In addition they offer evidence, via in vitro kinase assays applying GST-tagged ERR constructs, that several receptor sites (especially within the carboxy-terminus) may be phosphorylated by AKT and MAPK. Having said that, Chang et al. reported that in SKBR3 (a HER2-amplified, ER- breast cancer cell line), expression of endogenous ERR target genes is repressed by AKT, but not MAPK, inhibitors via regulation from the co-activator PGC1 . Moreover, they state that mapping and mutation from the proposed phosphorylation web sites in ERR has no effect on receptor transcriptional activity, which is in direct PDE3 Modulator supplier contrast to our getting that mutation of three ERK consensus web sites in ERR substantially impairs transcriptional activity and receptormediated TAM resistance. That ERR and ERR, in spite of their high sequence similarity and overlapping target genes, have differential functions in breast cancer is SIK3 Inhibitor drug definitely an concept that hasFEBS J. Author manuscript; readily available in PMC 2015 May 01.Heckler et al.Pagegained considerable traction lately [11, 44], and one that our future studies will address, particularly with respect to ERE- and ERRE-containing endogenous target gene selection (see below). We have been surprised by the apparent specificity of ERK for optimistic regulation of ERR in ER + breast cancer cells. All 3 members with the MAPK household (ERK, JNK, p38) can phosphorylate exactly the same S-P core motif, but our data show that only pharmacological inhibition of ERK reduces ERR protein. It need to be noted that beneath these experimental situations, p38 and JNK are expressed but their activation (phosphorylation) is minimal (Fig 2A, correct panels). We hence can’t rule out the possibility that in other contexts, ERR might have the capacity to be regulated by these other members on the MAPK household. It is not but clear how inhibition of ERK, or the S57,81,219A ERR mutation, in the end leads to a reduce in receptor levels. 1 reasonable explanation is really a change in proteasomalmediated degradation from the receptor such that phosphorylation of serines 57, 81, and/or 219 by ERK slows or prevents ubiquitination and degradation of ERR. Our information showing that a brief, 2 hour stimulation with EGF is adequate to improve ERR (HA) expression would be constant with this. Comparable to what we observe right here, MEK/ERK-mediated stabilization on the GLI2 oncoprotein final results in reduced ubiquitination of GLI2 that needs intact GSK3 phosphorylation internet sites . Parkin may be the only E3 ubiquitin ligase which has so far been shown to ubiquitinate ERR (and also other members in the ERR family members) , but understanding of whether/how parkin is impacted by ERK signaling in breast cancer is restricted. In neurons parkin and MAPKs do act in opposition to regulate microtubule depolymerization , and in numerous breast cancer cell lines parkin has been reported to bind microt.