Final Report Summary - ARL13B TRAFFICKING (Role of Arl13b in endocytic trafficking)
The aims of this project were to: a) determine the function of Arl13b in primary cilium cargo trafficking; b) define the mechanism by which Arl13b regulates endocytic trafficking; and c) identify Arl13b effectors.
We found that Arl13b interacts with the non-muscle myosin heavy chain IIA, or Myh9 and that this interaction is necessary for the binding of Arl13b to actin. Since Myh9 interacts with Arl13b in its GTP-bound form, we can conclude that Myh9 is the first bona fide effector found for Arl13b. Moreover, we found that Arl13b colocalizes with Myh9 in circular dorsal ruffles, which are actin-dependent structures that are involved in macropinocytosis and recycling of molecules such as integrins, as well as in cell migration. Interestingly, we showed that Arl13b is necessary for cell migration both in vitro and in vivo.
Strikingly, we discovered another effector for Arl13b, namely a subunit of the exocyst, a complex involved in tethering vesicles from the Golgi and the endocytic recycling compartment (ERC). Interestingly, it has recently been found that the exocyst is required for ciliogenesis and proper localization of ciliary cargo [6,7]. Hence, the interaction of Arl13b with the exocyst could represent the mechanism by which Arl13b regulates the trafficking of ciliary cargo between the ERC and cilia.
In conclusion, we found two bona fide effectors of Arl13b that could link its function in endocytic recycling, described by us, and in ciliogenesis, described by others.
References:
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2. Barral DC, Garg S, Casalou C, Watts GF, Sandoval JL, et al. (2012) Arl13b regulates endocytic recycling traffic. Proc Natl Acad Sci U S A 109: 21354-21359.
3. Cantagrel V, Silhavy JL, Bielas SL, Swistun D, Marsh SE, et al. (2008) Mutations in the Cilia Gene ARL13B Lead to the Classical Form of Joubert Syndrome. Am J Hum Genet.
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6. Fogelgren B, Lin SY, Zuo X, Jaffe KM, Park KM, et al. (2011) The Exocyst Protein Sec10 Interacts with Polycystin-2 and Knockdown Causes PKD-Phenotypes. PLoS Genet 7: e1001361.
7. Zuo X, Guo W, Lipschutz JH (2009) The exocyst protein Sec10 is necessary for primary ciliogenesis and cystogenesis in vitro. Mol Biol Cell 20: 2522-2529.