RESUMEN
Prokaryotic Cas1-Cas2 protein complexes generate adaptive immunity to mobile genetic elements (MGEs), by capture and integration of MGE DNA in to CRISPR sites. De novo immunity relies on naive adaptation-Cas1-Cas2 targeting of MGE DNA without the aid of pre-existing immunity 'interference' complexes-by mechanisms that are not clear. Using E. coli we show that the chaperone DnaK inhibits DNA binding and integration by Cas1-Cas2, and inhibits naive adaptation in cells that results from chromosomal self-targeting. Inhibition of naive adaptation was reversed by deleting DnaK from cells, by mutation of the DnaK substrate binding domain, and by expression of an MGE (phage λ) protein. We also imaged fluorescently labelled Cas1 in living cells, observing that Cas1 foci depend on active DNA replication, and are much increased in frequency in cells lacking DnaK. We discuss a model in which DnaK provides a mechanism for restraining naive adaptation from DNA self-targeting, until DnaK is triggered to release Cas1-Cas2 to target MGE DNA.
Asunto(s)
Proteínas Asociadas a CRISPR , Proteínas de Escherichia coli , Proteínas HSP70 de Choque Térmico , Repeticiones Palindrómicas Cortas Agrupadas y Regularmente Espaciadas , Proteínas Asociadas a CRISPR/metabolismo , Sistemas CRISPR-Cas , ADN/química , Escherichia coli/metabolismo , Proteínas de Escherichia coli/metabolismo , Proteínas HSP70 de Choque Térmico/metabolismoRESUMEN
Efforts to develop more effective therapies for acute leukemia may benefit from high-throughput screening systems that reflect the complex physiology of the disease, including leukemia stem cells (LSCs) and supportive interactions with the bone marrow microenvironment. The therapeutic targeting of LSCs is challenging because LSCs are highly similar to normal hematopoietic stem and progenitor cells (HSPCs) and are protected by stromal cells in vivo. We screened 14,718 compounds in a leukemia-stroma co-culture system for inhibition of cobblestone formation, a cellular behavior associated with stem-cell function. Among those compounds that inhibited malignant cells but spared HSPCs was the cholesterol-lowering drug lovastatin. Lovastatin showed anti-LSC activity in vitro and in an in vivo bone marrow transplantation model. Mechanistic studies demonstrated that the effect was on target, via inhibition of HMG-CoA reductase. These results illustrate the power of merging physiologically relevant models with high-throughput screening.
Asunto(s)
Antineoplásicos/farmacología , Ensayos de Selección de Medicamentos Antitumorales/métodos , Leucemia , Células Madre Neoplásicas/efectos de los fármacos , Línea Celular Tumoral , Células Madre Hematopoyéticas , Humanos , Inhibidores de Hidroximetilglutaril-CoA Reductasas/farmacología , Lovastatina/farmacología , Células Madre Neoplásicas/citología , Células Madre Neoplásicas/fisiologíaRESUMEN
Novel therapeutic approaches are urgently required for multiple myeloma (MM). We used a phenotypic screening approach using co-cultures of MM cells with bone marrow stromal cells to identify compounds that overcome stromal resistance. One such compound, BRD9876, displayed selectivity over normal hematopoietic progenitors and was discovered to be an unusual ATP non-competitive kinesin-5 (Eg5) inhibitor. A novel mutation caused resistance, suggesting a binding site distinct from known Eg5 inhibitors, and BRD9876 inhibited only microtubule-bound Eg5. Eg5 phosphorylation, which increases microtubule binding, uniquely enhanced BRD9876 activity. MM cells have greater phosphorylated Eg5 than hematopoietic cells, consistent with increased vulnerability specifically to BRD9876's mode of action. Thus, differences in Eg5-microtubule binding between malignant and normal blood cells may be exploited to treat multiple myeloma. Additional steps are required for further therapeutic development, but our results indicate that unbiased chemical biology approaches can identify therapeutic strategies unanticipated by prior knowledge of protein targets.