Merkel Cell Polyomavirus Large T Antigen Disrupts Lysosome Clustering by Translocating Human Vam6p from the Cytoplasm to the Nucleus

Abstract

Merkel cell polyomavirus (MCV) has been recently described as the cause for most human Merkel cell carcinomas. MCV is similar to simian virus 40 (SV40) and encodes a nuclear large T (LT) oncoprotein that is usually mutated to eliminate viral replication among tumor-derived MCV. We identified the hVam6p cytoplasmic protein involved in lysosomal processing as a novel interactor with MCV LT but not SV40 LT. hVam6p binds through its clathrin heavy chain homology domain to a unique region of MCV LT adjacent to the retinoblastoma binding site. MCV LT translocates hVam6p to the nucleus, sequestering it from involvement in lysosomal trafficking. A naturally occurring, tumor-derived mutant LT (MCV350) lacking a nuclear localization signal binds hVam6p but fails to inhibit hVam6p-induced lysosomal clustering. MCV has evolved a novel mechanism to target hVam6p that may contribute to viral uncoating or egress through lysosomal processing during virus replication.

Identification of an overprinting gene in Merkel cell polyomavirus provides evolutionary insight into the birth of viral genes

“…Although the LT expansion could be the result of neutral drift, it may have been selected for to facilitate additional protein-protein interactions. Consistent with this hypothesis, the expanded region in MCPyV LT is required for interactions with hVam6p, a cytoplasmic protein involved in lysosomal processing (30). A second feature that likely facilitated the birth of ALTO/MT was the presence of two highly conserved regions of LT that could encode important functional elements in the ALTO reading frame.…”

High-Affinity Rb Binding, p53 Inhibition, Subcellular Localization, and Transformation by Wild-Type or Tumor-Derived Shortened Merkel Cell Polyomavirus Large T Antigens

“…It thus may be more interesting to consider such a mechanism for other interaction partners of truncated LT-Ags, e.g., cellular proteins that bind to the unique ϳ110-amino-acid region which precedes the LxCxE region. Another interesting case is that of interaction partners that relocalize to the nucleus when complexed with fulllength LT-Ag but fail to do so upon interaction with the truncated protein, such as the lysosomal processing regulator hVam6p (66).…”

CORVET and HOPS tethering complexes–coordinators of endosome and lysosome fusion

“…Multiple interactions between HOPS or CORVET subunits and other proteins have been identified, including binding to actin and tubulin, and the cytoskeletal binding protein HOOK (Richardson et al, 2004;Xu et al, 2008), the interaction with components of the autophagy machinery (Liang et al, 2008), the Arl8 GTPase (Garg et al, 2011), which is involved in lysosomal mobility (Hofmann and Munro, 2006;Mrakovic et al, 2012), Merkel virus (Liu et al, 2011) and the AP-3 complex (Zlatic et al, 2011a). Furthermore, HOPS/CORVET subunits have been identified on clathrin-coated vesicles (Zlatic et al, 2011a), as well as on late endosomes and lysosomes (Poupon et al, 2003;Pols et al, 2012;Sriram et al, 2003;Swetha et al, 2011), which suggests a role for HOPS/CORVET in endosomal fusion and even maturation.…”