Regulatory function of the P295-T311 motif of the estrogen receptor α - does proteasomal degradation of the receptor induce emergence of peptides implicated in estrogenic responses?

The way in which estrogen receptor α (ERα) mediates gene transcription and hormone-dependent cancer cell proliferation is now being largely reconsidered in view of several recent discoveries. ERα-mediated transcription appears to be a cyclic and transient process where the proteasome - and thus receptor degradation - plays a pivotal role. In view of our recent investigations, which demonstrate the estrogenic activity of a synthetic peptide corresponding to a regulatory motif of the receptor (ERα17p), we propose that ERα proteasomal degradation could induce the emergence of regulatory peptide(s). The latter would function as a signal and contribute to the ERα activation process, amplifying the initial hormonal stimulation and giving rise to sustained estrogenic response

Molecular basis of agonistic activity of ERa17p, a synthetic peptide corresponding to a sequence located at the N-terminal part of the estrogen receptor a ligand binding domain

info:eu-repo/semantics/publishe

Molecular basis of agonistic activity of ERα17p, a synthetic peptide corresponding to a sequence located at the N-terminal part of the estrogen receptor α ligand binding domain

SCOPUS: ar.jinfo:eu-repo/semantics/publishe

Specificity and reversibility of the transpeptidation reaction catalyzed by the Streptomyces R61 D-Ala-D-Ala peptidase

The specificity of the Streptomyces R61 penicillin-sensitive D-Ala-D-Ala peptidase has been re-examined with the help of synthetic substrates. The products of the transpeptidation reactions obtained with Gly-L-Xaa dipeptides as acceptor substrates are themselves poor substrates of the enzyme. This is in apparent contradiction with the classically accepted specificity rules for D-Ala-D-Ala peptidases. The Gly-L-Xaa dipeptide is regenerated by both the hydrolysis and transpeptidation reactions. The latter reaction is observed when another Gly-L-Xaa peptide or D-Alanine are supplied as acceptors. Utilization of substrates in which the terminal -COO− group has been esterified or amidated shows that a free carboxylate is not an absolute prerequisite for activity. The results are discussed in the context of the expected reversibilty of the transpeptidation reaction

Trophic effect in MCF-7 cells of ERalpha17p, a peptide corresponding to a platform regulatory motif of the estrogen receptor alpha--underlying mechanisms.

As yet, estrogen receptor alpha (ERalpha) inhibitors used in clinical practice target a unique site, i.e. the hormone-binding pocket. With the aim of discovering other potential therapeutic targets in the receptor, we studied its AF-2a domain, a site that proves to be critical for ligand-independent ERalpha activity. Previous studies from our laboratory highlighted an auto-inhibitory action associated with a site included in this domain, i.e. the P295-T311 sequence. Accordingly, a deletion of this sequence produces a constitutively activated receptor mutant. More interestingly, a synthetic peptide with the P295-T311 sequence (ERalpha17p) elicits in breast cancer cell lines estrogenic responses that may be ascribed to a competitive mechanism towards the P295-T311-associated auto-inhibition of ERalpha. In the present study, we show that ERalpha17p sustains MCF-7 cell growth in estrogen-depleted culture medium by inducing molecular events promoting G1/S phase transition. We demonstrate, moreover, that this proliferative activity is associated with receptor down regulation (acceleration of ERalpha degradation and repression of ESR1 gene transcription), similar to that induced by estrogen agonists. Complementary studies suggest that our observations may be, at least in part, relevant to a competitive inhibition affecting ERalpha-Hsp70 association. Hence, the design of drugs able to stabilize ERalpha-Hsp70 complexes - where the receptor is in an inactive conformation - may be of therapeutic value.Journal ArticleResearch Support, Non-U.S. Gov'tSCOPUS: ar.jinfo:eu-repo/semantics/publishe

Calmodulin-independent, agonistic properties of a peptide containing the calmodulin binding site of estrogen receptor α

Calmodulin (CaM) contributes to estrogen receptor α (ER)-mediated transcription. In order to study the underlying mechanisms, we synthesized a peptide including the CaM binding site: ERα17p (P295-T311). This peptide inhibited ER-CaM association, unlike two analogs in which two amino acids required for CaM binding were substituted. Exposure of MCF-7 cells to ERα17p down regulated ER, stimulated ER-dependent transcription and enhanced the proliferation of ER-positive breast cancer cell lines. Interestingly, ERα17p analogs unable to bind to CaM induced similar responses, demonstrating that ERα17p-mediated effects are mainly relevant to mechanisms independent of ER-CaM dissociation. The P295-T311 motif is indeed a platform for multiple post-translational modifications not necessarily CaM-dependent. The additional finding that deletion of the P295-T311 sequence in ER produced a constitutive transcriptional activity revealed that this platform motif has autorepressive functions. With regard to cell function, association of CaM to ER would counteract this autorepression, leading thereby to enhanced ER-mediated transactivation. © 2007 Elsevier Ireland Ltd. All rights reserved.SCOPUS: ar.jinfo:eu-repo/semantics/publishe