RESUMO
Induction of estrogen-regulated gene transcription by estrogen receptors ERalpha and ERbeta plays an important role in breast cancer development and growth. High expression of the chemokine receptor CXCR4 and its ligand CXCL12/stromal cell-derived factor 1 (SDF-1) has also been correlated with aggressive breast tumor phenotypes. Here, we describe a positive regulatory loop between the CXCR4/SDF-1 signaling pathway and ER transcriptional competence in human breast cancer cells. Treatment of breast carcinoma MCF-7 cells with SDF-1 increased ER transcriptional activity and expression of ER target genes, including SDF-1 itself. These effects were blocked by the antiestrogen ICI-182780 and by CXCR4 silencing and, conversely, estrogen-induced gene expression and growth of MCF-7 cells were impaired on CXCR4 inhibition. Both ERalpha and ERbeta were activated by SDF-1 in the presence of CXCR4 and by overexpression of a constitutively active CXCR4, indicating that CXCR4 signals to both receptors. In particular, ERbeta was able to translate the effects of SDF-1 on its own expression, as well as enhance activator protein 1 (AP-1) containing genes cyclin D1 and c-Myc in the presence of tamoxifen. This correlated with an increased ERbeta occupancy of responsive promoters at both estrogen-responsive and AP-1 elements. Ser-87, a conserved mitogen-activated protein kinase site in ERbeta, was highly phosphorylated by SDF-1, revealing an essential role of the AF-1 domain in response to CXCR4 activation. These results identify a complete autocrine loop between the CXCR4/SDF-1 and ERalpha/ERbeta signaling pathways that dictates ER-dependent gene expression and growth of breast cancer cells.
Assuntos
Quimiocina CXCL12/genética , Receptores CXCR4/genética , Receptores de Estrogênio/genética , Transdução de Sinais/genética , Sítios de Ligação/genética , Western Blotting , Linhagem Celular , Linhagem Celular Tumoral , Quimiocina CXCL12/metabolismo , Quimiocina CXCL12/farmacologia , Receptor alfa de Estrogênio/genética , Receptor alfa de Estrogênio/metabolismo , Receptor beta de Estrogênio/genética , Receptor beta de Estrogênio/metabolismo , Estrogênios/farmacologia , Regulação Neoplásica da Expressão Gênica/efeitos dos fármacos , Humanos , Fosforilação/efeitos dos fármacos , Receptores de Estrogênio/metabolismo , Reação em Cadeia da Polimerase Via Transcriptase Reversa , Serina/genética , Serina/metabolismo , Transdução de Sinais/efeitos dos fármacos , Tamoxifeno/farmacologia , Fatores de Tempo , Fator de Transcrição AP-1/metabolismoRESUMO
A new class of mu selective receptor antagonists has been developed using a combinatorial approach based on previously reported Dmt-Tic dipeptide ligands. Modified tetrahydroisoquinoline (Tiq) residues were reacted with different electrophiles in order to create novel molecules that would mimic the original dipeptide. A specific class of thioureas bearing basic pyrrolidine residues were shown to give good binding affinities. Further alkylation of the pyrrolidine ring with benzyl derivatives also proved to increase the mu binding affinity. In addition, it was demonstrated that mu binding was enhanced by the presence of polar groups around the benzyl ring having hydrogen-bonding character (donor/acceptor). This new class of ligands represents a novel scaffold in the development of opioid analogues.
