RESUMEN
Maintenance of the intestinal epithelium requires constant self-renewal and regeneration. Tight regulation of proliferation and differentiation of intestinal stem cells within the crypt region is critical to maintaining homeostasis. The transcriptional co-factors ß-catenin and YAP are required for proliferation during normal homeostasis as well as intestinal regeneration after injury: aberrant signaling activity results in over proliferation and tumorigenesis. Although both YAP and ß-catenin activity are controlled along canonical pathways, it is becoming increasingly clear that non-canonical regulation of these transcriptional regulators plays a role in fine tuning their activity. We have shown previously that MAMDC4 (Endotubin, AEGP), an integral membrane protein present in endosomes, regulates both YAP and ß-catenin activity in kidney epithelial cells and in the developing intestinal epithelium. Here we show that MAMDC4 interacts with members of the signalosome and mediates cross-talk between YAP and ß-catenin. Interestingly, this cross-talk occurs through a non-canonical pathway involving interactions between AMOT:YAP and AMOT:ß-catenin.
Asunto(s)
Proteínas Adaptadoras Transductoras de Señales , Endosomas , Factores de Transcripción , Vía de Señalización Wnt , beta Catenina , Humanos , beta Catenina/metabolismo , Endosomas/metabolismo , Factores de Transcripción/metabolismo , Factores de Transcripción/genética , Animales , Proteínas Adaptadoras Transductoras de Señales/metabolismo , Proteínas Adaptadoras Transductoras de Señales/genética , Proteínas Señalizadoras YAP/metabolismo , Fosfoproteínas/metabolismo , Fosfoproteínas/genética , Ratones , Proteínas de la Membrana/metabolismo , Proteínas de la Membrana/genética , Células HEK293 , Proteínas de Ciclo Celular/metabolismo , Proteínas de Ciclo Celular/genética , Unión ProteicaRESUMEN
During postnatal intestinal development, the intestinal epithelium is highly proliferative, and this proliferation is regulated by signaling in the intervillous and crypt regions. This signaling is primarily mediated by Wnt, and requires membrane trafficking. However, the mechanisms by which membrane trafficking regulates signaling during this developmental phase are largely unknown. Endotubin (EDTB, MAMDC4) is an endosomal protein that is highly expressed in the apical endocytic complex (AEC) of villus enterocytes during fetal and postnatal development, and knockout of EDTB results in defective formation of the AEC and giant lysosome. Further, knockout of EDTB in cell lines results in decreased proliferation. However, the role of EDTB in proliferation during the development of the intestine is unknown. Using Villin-CreERT2 in EDTBfl/fl mice, we deleted EDTB in the intestine in the early postnatal period, or in enteroids in vitro after isolation of intervillous cells. Loss of EDTB results in decreased proliferation in the developing intestinal epithelium and decreased ability to form enteroids. EDTB is present in cells that contain the stem cell markers LGR5 and OLFM4, indicating that it is expressed in the proliferative compartment. Further, using immunoblot analysis and TCF/LEF-GFP mice as a reporter of Wnt activity, we find that knockout of EDTB results in decreased Wnt signaling. Our results show that EDTB is essential for normal proliferation during the early stages of intestinal development and suggest that this effect is through modulation of Wnt signaling.
Asunto(s)
Proliferación Celular/genética , Glicoproteínas/genética , Intestinos/embriología , Animales , Diferenciación Celular/genética , Proliferación Celular/fisiología , Endosomas/metabolismo , Enterocitos/metabolismo , Femenino , Glicoproteínas/metabolismo , Mucosa Intestinal/metabolismo , Intestinos/metabolismo , Masculino , Ratones , Ratones Noqueados , Proteínas de Microfilamentos/genética , Proteínas Wnt/metabolismo , Vía de Señalización Wnt/fisiologíaRESUMEN
Membrane trafficking establishes and maintains epithelial polarity. Rab22a has a polarized distribution in activated T-cells, but its role in epithelial polarity has not been investigated. We showed previously that Rab14 acts upstream of Arf6 to establish the apical membrane initiation site (AMIS), but its interaction with Rab22a is unknown. Here we show that Rab14 and Rab22a colocalize in endosomes of both unpolarized and polarized MDCK cells and Rab22a localizes to the cell:cell interface of polarizing cell pairs. Knockdown of Rab22a results in a multi-lumen phenotype in three-dimensional culture. Further, overexpression of Rab22a in Rab14 knockdown cells rescues the multi-lumen phenotype observed with Rab14 knockdown, suggesting that Rab22a is downstream of Rab14. Because of the relationship between Rab14 and Arf6, we investigated the effect of Rab22a knockdown on Arf6. We find that Rab22a knockdown results in decreased active Arf6 and that Rab22a co-immunoprecipitates with the Arf6 GEF EFA6. In addition, EFA6 is retained in intracellular puncta in Rab22a KD cells. These results suggest that Rab22a acts downstream of Rab14 to traffic EFA6 to the AMIS to regulate Arf6 in the establishment of polarity.