Rab11A forms a complex with Interferon Regulatory Factor 6 in recycling endosomes

Abstract

Interferon Regulatory Factor 6 (IRF6) is a transcription factor essential for regulating keratinocyte migration, proliferation and differentiation. Structurally, the IRF6 protein includes a DNA binding domain (DBD), a protein binding domain (PBD), and a serine rich autoinhibitory region (SRR). Historically, IRF6 has been assumed to play its role by regulating gene expression, however growing evidence suggest that some of its functions may be dependent on protein‐protein interactions. Although the effect of such interactions on the regulated proteins remains to be elucidated, some groups have proposed a protective role for IRF6 preventing protein degradation. Alternatively, we hypothesize that IRF6 may also play a scaffolding function regulating the subcellular localization of effector proteins. We recently demonstrated that IRF6 is required for the delivery of E‐cadherin to the plasma membrane. More specifically, we found that recycling of E‐cadherin was defective in absence of IRF6. Interestingly, the total E‐cadherin levels were not altered in the absence of IRF6, and under culture conditions used to test keratinocyte adhesion behavior, IRF6 was not detected in the nucleus. To explore the molecular mechanism used by IRF6 to regulate E‐cadherin at the plasma membrane, we investigated whether IRF6 colocalized with NME1 and NME2, two proteins known to internalize E‐cadherin towards recycling endosomes and regulate the secretory pathway, respectively. We found that in our experimental conditions NME2 does not colocalize with IRF6. However, by immunofluorescence, IRF6 and NME1 colocalize and their mutual coimmunoprecipitation suggest they are part of the same complex. Because NME1 is necessary for E‐cadherin recycling, we hypothesized that IRF6‐NME1 regulates recycling endosome function. To test our hypothesis, we evaluated the interaction between E‐cadherin, IRF6 and Rab11A, a required promoter of recycling endosome. Our results show that Rab11A colocalizes with all these proteins in recycling endosomes, and that IRF6, Rab11A and NME1 coimmunoprecipitated with each other, suggesting that they belong to the same complex. Overall, our results suggest that IRF6 participate in a complex with Rab11A and NME1, potentially modulating recycling endosome function and promoting the recyling of Ecadherin.