Identification of the universal cofactor (auxilin 2) in clathrin coat dissociation

A Umeda, A Meyerholz, E Ungewickell - European journal of cell biology, 2000 - Elsevier
A Umeda, A Meyerholz, E Ungewickell
European journal of cell biology, 2000Elsevier
Uncoating of clathrin-coated vesicles in neuronal cells requires hsc70 in concert with the
cofactor auxilin which contains a J-domain as well as a domain with homology to dual
specific phosphatases and tensin, known as PTEN. The question of whether an analogous
factor operates in other cell types has until now remained unanswered. Here we show that it
is the recently discovered and widely expressed cyclin G-associated protein kinase which
fulfils the function of neuronal auxilin in hsc70-mediated clathrin coat dissociation. GAK …
Summary
Uncoating of clathrin-coated vesicles in neuronal cells requires hsc70 in concert with the cofactor auxilin which contains a J-domain as well as a domain with homology to dual specific phosphatases and tensin, known as PTEN. The question of whether an analogous factor operates in other cell types has until now remained unanswered. Here we show that it is the recently discovered and widely expressed cyclin G-associated protein kinase which fulfils the function of neuronal auxilin in hsc70-mediated clathrin coat dissociation. GAK possesses a J-domain, which stimulates the hsc70 ATPase, it competes with auxilin for clathrin binding and at sufficiently high concentrations acts as a clathrin assembly protein. Moreover, GAK binds to the γ- and α-appendage domains of the adaptor proteins AP-1 and AP-2 in vitro and phosphorylates their medium chains. Cells that transiently overexpress GAK are impaired in respect of receptor-mediated endocytosis. In transfected cells clathrin is dislodged from coated pits/vesicles and co-localizes with GFP-GAK in the form of large aggregates. The cellular distribution of membrane-associated adaptors was unaffected by overexpression of GAK. Our results point to a hsc70/auxilin-based uncoating system as a ubiquitous feature of eukaryotic cells.
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