Junction-mediating and regulatory protein (JMY) was originally identified as a transcriptional co-factor in the p53-response to DNA damage. Aside from this nuclear function, recent years have uncovered an additional function of JMY, namely in cytoskeleton remodelling and actin assembly. The C-terminus of JMY comprises a canonical VCA-module, the sequence signature of Arp2/3 complex activators. Furthermore, tandem repeats of 3 WH2 (V, or more recently also W) domains render JMY capable of Arp2/3 independent actin assembly. The motility promoting cytoplasmic function of JMY is abrogated upon DNA-damage and nuclear translocation of JMY. To address the precise cellular function of JMY in cellular actin rearrangements, we have searched for potential new interaction partners by mass spectrometry. We identified several candidates and correlated their localization with the subcellular dynamics of JMY. JMY is localized to dynamic vesiculo-tubular structures throughout the cytoplasm, which are decorated with actin and Arp2/3 complex. Moreover, JMY partially colocalizes and interacts with VAP-A, which is involved in vesicle-based transport processes. Finally, overexpression of JMY results in Golgi dispersal by loss from the trans-site and affects VSV-G transport. These analyses, together with biochemical experiments, indicate that JMY drives vesicular trafficking in the trans-Golgi region and at ER-membrane contact sites (MCS), distinct from other Arp2/3 activators involved in vesicle transport processes such as the related WHAMM or WASH.
Keywords: Actin dynamics; Arp2/3 complex; Golgi; JMY; NPF; Nucleation promoting factors; Tubular vesicles; Vesicle traffic; WHAMM.
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