RESUMO
Despite their initial effectiveness in the treatment of melanoma, chemotherapeutic agents are ultimately futile against this most aggressive form of skin cancer, and patients inevitably succumb to the disease. One of the mechanisms by which residual melanoma cells become chemoresistant is via the decreased efficiency of chemotherapeutics through the action of ATP-binding cassette (ABC) proteins that are variably expressed by the tumor cells. The clinical relevance of the ABC transporters in the context of cancer is paramount. Inhibitors of these transporters have been shown to increase the efficacy of standard therapy in experimental systems. Their clinical application requires better understanding of the role individual transporters play in the mechanism and the development of more specific inhibitors with minimal off target effects. ABC transporters in tumor cells have been shown to confer multidrug resistance in many solid tumors. However, their role in melanomas is far from clear. Here, we prospectively identify ABCB8 as a specific and major player in the chemoresistance of several melanoma cell lines. ABCB8 knockdown with shRNA reduced doxorubicin resistance approximately 3- to 4-fold in these cells. Furthermore, we show that this reversal is specific to doxorubicin and not to other commonly used chemotherapeutics. Our results also provide evidence that ABCB8 conferred resistance through the protection of mitochondrial DNA from doxorubicin-induced DNA damage.
Assuntos
Transportadores de Cassetes de Ligação de ATP/genética , DNA Mitocondrial/genética , Doxorrubicina/farmacologia , Resistencia a Medicamentos Antineoplásicos/genética , Genoma/efeitos dos fármacos , Melanoma/genética , Neoplasias Cutâneas/genética , Transportador 1 de Cassete de Ligação de ATP , Transportadores de Cassetes de Ligação de ATP/efeitos dos fármacos , Linhagem Celular Tumoral , Primers do DNA , DNA Mitocondrial/efeitos dos fármacos , Doxorrubicina/uso terapêutico , Humanos , Melanoma/tratamento farmacológico , Reação em Cadeia da Polimerase , RNA Neoplásico/efeitos dos fármacos , RNA Neoplásico/genética , Neoplasias Cutâneas/tratamento farmacológicoRESUMO
We used an in vivo small hairpin RNA (shRNA) screening approach to identify genes that are essential for MLL-AF9 acute myeloid leukemia (AML). We found that Integrin Beta 3 (Itgb3) is essential for murine leukemia cells in vivo and for human leukemia cells in xenotransplantation studies. In leukemia cells, Itgb3 knockdown impaired homing, downregulated LSC transcriptional programs, and induced differentiation via the intracellular kinase Syk. In contrast, loss of Itgb3 in normal hematopoietic stem and progenitor cells did not affect engraftment, reconstitution, or differentiation. Finally, using an Itgb3 knockout mouse model, we confirmed that Itgb3 is dispensable for normal hematopoiesis but is required for leukemogenesis. Our results establish the significance of the Itgb3 signaling pathway as a potential therapeutic target in AML.