Cell biological characterization of the Cohen syndrome‐associated protein COH1 (894.1)

Abstract

Mutations in COH1 (VPS13B) cause autosomal recessive Cohen syndrome, which is mainly characterized by mental retardation, progressive postnatal microcephaly, facial dysmorphism and progressive retinopathy/myopia, and intermittent neutropenia. Recently, our cell biological analysis identified COH1 as peripheral membrane protein of 3997 amino acids at the cytosolic site of the Golgi apparatus. Initial analysis showed that loss of COH1 upon RNAi impairs the ability of the Golgi ribbon to (re)assemble and thus induces fragmentation into mini‐stacks. Subsequential BFA‐treatment indicates that COH1 regulates the formation of Golgi‐derived membrane tubules consistent with a potential function in intracellular membrane traffic. To further investigate the intracellular function of COH1, we will estimate its impact on endo‐ and exocytosis by live cell imaging analysis of well‐established cargo proteins, such as GFP‐VSVGtsO45, Alexa488‐EGF, and Alexa555‐Tf. Complementary, we will assess a COH1‐protein interaction network with special focus on small GTPases, using different methods, e.g. GST‐pull downs and co‐immunoprecipitations followed by Western blot analysis and mass spectroscopy. The hitherto identified interaction partners become investigated related to their function in transportation, cell polarization, cell migration and ways of signal transduction in neuronal cells. In summary, our study until now identifies COH1 as a Golgi matrix protein required for maintaining Golgi integrity and function. We suggest that our results provide an improved insight into the molecular function of COH1 in Golgi‐associated membrane traffic which in the future may help to unravel its role in brain development, neuronal function, and general pathology in patients with Cohen syndrome.