RESUMEN
Proper temporal and spatial activation of stem cells relies on highly coordinated cell signaling. The primary cilium is the sensory organelle that is responsible for transmitting extracellular signals into a cell. Primary cilium size, architecture, and assembly-disassembly dynamics are under rigid cell cycle-dependent control. Using mouse incisor tooth epithelia as a model, we show that ciliary dynamics in stem cells require the proper functions of a cholesterol-binding membrane glycoprotein, Prominin-1 (Prom1/CD133), which controls sequential recruitment of ciliary membrane components, histone deacetylase, and transcription factors. Nuclear translocation of Prom1 and these molecules is particularly evident in transit amplifying cells, the immediate derivatives of stem cells. The absence of Prom1 impairs ciliary dynamics and abolishes the growth stimulation effects of sonic hedgehog (SHH) treatment, resulting in the disruption of stem cell quiescence maintenance and activation. We propose that Prom1 is a key regulator ensuring appropriate response of stem cells to extracellular signals, with important implications for development, regeneration, and diseases.
Asunto(s)
Antígeno AC133/metabolismo , Cilios/metabolismo , Incisivo/citología , Antígeno AC133/genética , Animales , Núcleo Celular/metabolismo , Células Cultivadas , Humanos , Incisivo/metabolismo , Ratones , Modelos Biológicos , Mutagénesis Sitio-Dirigida , Transporte de Proteínas , Transducción de Señal , Células Madre/citología , Células Madre/metabolismoRESUMEN
Huntington's disease (HD) is caused by a polyglutamine (polyQ) expansion in the huntingtin (htt) protein. While aggregation is a pathological hallmark of HD and related polyQ expansion diseases, the role of aggregates has been disputed. Here we report that p21-activated kinase 1 (Pak1) binds to htt in vivo and in vitro. Pak1 colocalized with mutant htt (muhtt) aggregates in cell models and in human HD brains. Pak1 overexpression enhanced the aggregation of muhtt. Furthermore, we observed SDS-soluble wild-type htt (wthtt)-wthtt, wthtt-muhtt and muhtt-muhtt interactions, which were enhanced by the presence of Pak1. We show that Pak1 overexpression enhanced htt toxicity in cell models and neurons in parallel with its ability to promote aggregation, while Pak1 knockdown suppressed both aggregation and toxicity. Overexpression of either kinase-dead or wild-type Pak enhanced both aggregation and toxicity. Our data reveal a novel mechanism regulating muhtt oligomerization and toxicity and suggest that pathology may be at least partly dependent on soluble muhtt-muhtt interactions.