RESUMO
The non-receptor tyrosine kinase ABL drives myeloid progenitor expansion in human chronic myeloid leukemia. ABL inhibition by the tyrosine kinase inhibitor nilotinib is a first-line treatment for this disease. Recently, ABL has also been implicated in the transforming properties of solid tumors, including triple negative (TN) breast cancer. TN breast cancers are highly metastatic and several cell lines derived from these tumors display high invasive activity in vitro. This feature is associated with the activation of actin-rich membrane structures called invadopodia that promote extracellular matrix degradation. Here, we investigated nilotinib effect on the invasive and migratory properties of different TN breast cancer cell lines. Nilotinib decreased both matrix degradation and invasion in the TN breast cancer cell lines MDA-MB 231 and MDA-MB 468. However, and unexpectedly, nilotinib increased by two-fold the invasive properties of the TN breast cancer cell line BT-549 and of Src-transformed fibroblasts. Both display much higher levels of ABL kinase activity compared to MDA-MB 231. Similar effects were obtained by siRNA-mediated down-regulation of ABL expression, confirming ABL central role in this process. ABL anti-tumor effect in BT-549 cells and Src-transformed fibroblasts was not dependent on EGF secretion, as recently reported in neck and squamous carcinoma cells. Rather, we identified the TRIO-RAC1 axis as an important downstream element of ABL activity in these cancer cells. In conclusion, the observation that TN breast cancer cell lines respond differently to ABL inhibitors could have implications for future therapies.
Assuntos
Antineoplásicos/farmacologia , Inibidores de Proteínas Quinases/farmacologia , Proteínas Proto-Oncogênicas c-abl/metabolismo , Neoplasias de Mama Triplo Negativas/metabolismo , Comunicação Autócrina , Linhagem Celular Tumoral , Movimento Celular/efeitos dos fármacos , Transformação Celular Neoplásica/genética , Transformação Celular Neoplásica/metabolismo , Feminino , Fibroblastos/metabolismo , Fibroblastos/patologia , Fator de Crescimento Semelhante a EGF de Ligação à Heparina/metabolismo , Humanos , Proteínas Proto-Oncogênicas c-abl/antagonistas & inibidores , Proteínas Proto-Oncogênicas c-abl/genética , Pirimidinas/farmacologia , Neoplasias de Mama Triplo Negativas/genética , Neoplasias de Mama Triplo Negativas/patologia , Proteínas rac1 de Ligação ao GTP/genética , Proteínas rac1 de Ligação ao GTP/metabolismo , Quinases da Família src/genética , Quinases da Família src/metabolismoRESUMO
The Rho GTPases RhoA and Rac1 function as master regulators of cytokinesis by controlling the actomyosin cytoskeleton. RhoA and Rac1 have to be respectively activated and inactivated at the division plane for cytokinesis to occur properly. The inactivation of Rac1 at the cleavage furrow is controlled by MgcRacGAP. However, the guanine-nucleotide exchange factor (GEF) that activates Rac1 during cell division remains unknown. Here, using a siRNA screening approach in HeLa cells, we identify Trio as a mitotic GEF of Rac1. We demonstrate that Trio controls Rac1 activation and subsequent F-actin remodeling in dividing cells. Moreover, Trio depletion specifically rescues the cytokinesis failure induced by MgcRacGAP depletion. Of importance, we demonstrate that this rescue is mediated by the Trio-Rac1 pathway, using GEF-dead mutants of Trio and a specific inhibitor of Rac1 activation by Trio. Overall this work identifies for the first time a GEF controlling Rac1 activation in dividing cells that counteracts MgcRacGAP function in cytokinesis.
