RESUMO
Estrogen receptor-alpha (ERalpha) is a major therapeutic target of hormonal therapies in breast cancer, and its expression in tumors is predictive of clinical response. Protein levels of ERalpha are tightly controlled by the 26S proteasome; yet, how the clinical proteasome inhibitor, bortezomib, affects ERalpha regulation has not been studied. Bortezomib selectively inhibits the chymotrypsin-like activity of the proteasome. Unlike other laboratory proteasome inhibitors, bortezomib failed to stabilize ERalpha protein at a dose exceeding 90% inhibition of the chymotrypsin-like activity. Unexpectedly, however, chronic bortezomib exposure caused a reduction of ERalpha levels in multiple ER+ breast cancer cell lines. This response can be explained by the fact that bortezomib induced a dramatic decrease in ERalpha mRNA because of direct transcriptional inhibition and loss of RNA polymerase II recruitment on the ERalpha gene promoter. Bortezomib treatment resulted in promoter-specific changes in estrogen-induced gene transcription that related with occupancy of ERalpha and RNA polymerase II (PolII) on endogenous promoters. In addition, bortezomib inhibited estrogen-dependent growth in soft agar. These results reveal a novel link between proteasome activity and expression of ERalpha in breast cancer and uncover distinct roles of the chymotrypsin-like activity of the proteasome in the regulation of the ERalpha pathway.
Assuntos
Ácidos Borônicos/farmacologia , Receptor alfa de Estrogênio/metabolismo , Inibidores de Proteassoma , Pirazinas/farmacologia , Western Blotting , Bortezomib , Neoplasias da Mama/genética , Neoplasias da Mama/metabolismo , Neoplasias da Mama/patologia , Linhagem Celular Tumoral , Quimotripsina/antagonistas & inibidores , Quimotripsina/metabolismo , Relação Dose-Resposta a Droga , Receptor alfa de Estrogênio/genética , Estrogênios/farmacologia , Feminino , Regulação Neoplásica da Expressão Gênica/efeitos dos fármacos , Humanos , Cinética , Regiões Promotoras Genéticas/genética , Inibidores de Proteases/farmacologia , Complexo de Endopeptidases do Proteassoma/metabolismo , RNA Polimerase II/metabolismo , Reação em Cadeia da Polimerase Via Transcriptase Reversa , Transdução de SinaisRESUMO
The purpose of this article is to provide physicians in private practice with a methodology for shaping their own destinies and to ensure they will be able to cope successfully with the current changes, as well as those yet to come, that will impact on their practices. It attempts to highlight those core techniques employed in long-term and strategic planning, enabling them to understand what the planning process is all about.
