Inhibition of Retromer Activity by Herpesvirus Saimiri Tip Leads to CD4 Downregulation and Efficient T Cell Transformation

Abstract

The mammalian retromer is an evolutionally conserved protein complex composed of a vacuolar protein sorting trimer (Vps 26/29/35) that participates in cargo recognition and a sorting nexin (SNX) dimer that binds to endosomal membranes. The retromer plays an important role in efficient retrograde transport for endosome-to-Golgi retrieval of the cation-independent mannose-6-phosphate receptor (CI-MPR), a receptor for lysosomal hydrolases, and other endosomal proteins. This ultimately contributes to the control of cell growth, cell adhesion, and cell migration. The herpesvirus saimiri (HVS) tyrosine kinase-interacting protein (Tip), required for the immortalization of primary T lymphocytes, targets cellular signaling molecules, including Lck tyrosine kinases and the p80 endosomal trafficking protein. Despite the pronounced effects of HVS Tip on T cell signal transduction, the details of its activity on T cell immortalization remain elusive. Here, we report that the amino-terminal conserved, glutamate-rich sequence of Tip specifically interacts with the retromer subunit Vps35 and that this interaction not only causes the redistribution of Vps35 from the early endosome to the lysosome but also drastically inhibits retromer activity, as measured by decreased levels of CI-MPR and lower activities of cellular lysosomal hydrolases. Physiologically, the inhibition of intracellular retromer activity by Tip is ultimately linked to the downregulation of CD4 surface expression and to the efficient in vitro immortalization of primary human T cells to interleukin-2 (IL-2)-independent permanent growth. Therefore, HVS Tip uniquely targets the retromer complex to impair the intracellular trafficking functions of infected cells, ultimately contributing to efficient T cell transformation.

Retromer: A Master Conductor of Endosome Sorting

“…CSC deficiency plays a role in nonamyloidogenic versus amyloidogenic processing of amyloid precursor protein (APP) (He et al 2005;Small et al 2005;Muhammad et al 2008;Wen et al 2011;Choy et al 2012) and the pathogenesis of Alzheimer's disease (Siegenthaler and Rajendran 2012). In addition, a specific VPS35 mutation, Asp620Asn, has been linked to late-onset autosomal-dominant familial Parkinson's disease (Vilariño-Güell et al 2011;Zimprich et al 2011), the loci for human VPS26A has been genetically associated with type 2 diabetes in South Asians (Kooner et al 2011), and the endosomal transport of various pathogens (Salmonella, Herpesvirus saimiri, Coxiella burnetii, human papillomavirus, Legionella pneumophila) and toxins (Shiga toxin) is also mediated in part by the CSC Popoff et al 2007;Kingston et al 2011;Finsel et al 2013;Lipovsky et al 2013;McDonough et al 2013). …”

Genome-wide siRNA screen identifies the retromer as a cellular entry factor for human papillomavirus

“…The 293T cells were transfected with genes encoding myc-tagged VPS26, VPS29, and VPS35, or an empty vector (44). Thirty hours later, cells were infected with HPV16.L2HA-GFP at an MOI of 50 for 8 h and then lysed in buffer containing 1% Nonidet P-40.…”

The retromer complex – endosomal protein recycling and beyond

“…Snx3 has been implicated in the maturation of Salmonella-containing endosomes, although it is not yet clear whether in this role Snx3 is associated with retromer proteins (Braun et al, 2010). Additionally, the Tip protein of Herpes virus can bind to Vps35 to inhibit retromer function, leading to reduced CIMPR levels and downregulation of CD4 (Kingston et al, 2011), and entry of Vaccinia virus has been shown to require the Fam21 subunit of the WASH complex (Huang et al, 2008).…”