Human Papillomavirus L2 Facilitates Viral Escape from Late Endosomes via Sorting Nexin 17

Abstract

The Human Papillomavirus (HPV) L2 capsid protein plays an essential role during the early stages of viral infection, but the molecular mechanisms underlying its mode of action remain obscure. Using a proteomic approach we have identified the adaptor protein, Sorting Nexin 17 (SNX17) as a strong interacting partner of HPV L2. This interaction occurs through a highly conserved SNX17 consensus binding motif, which is present in the majority of HPV L2 proteins analysed. Using mutants of L2 defective for SNX17 interaction, or siRNA ablation of SNX17 expression we demonstrate that the interaction between L2 and SNX17 is essential for viral infection. Furthermore, loss of the L2-SNX17 interaction results in enhanced turnover of the L2 protein and decreased stability of the viral capsids, and concomitantly there is a dramatic decrease in the efficiency with which viral genomes transit to the nucleus. Indeed, using a range of endosomal and lysosomal markers we show that capsids defective in their capacity to bind SNX17 transit much more rapidly to the lysosomal compartment. These results demonstrate that the L2-SNX17 interaction is essential for viral infection and facilitates the escape of the L2-DNA complex from the late endosomal/lysosomal compartments.

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

“…However, the retromer is in the cytoplasm whereas the incoming virus is initially in the lumen of the endosome. We speculate either that the virus "piggybacks" a ride with a cellular retromer cargo or adapter protein [such as sorting nexin 17 (22,40)], which extends across the endosomal membrane, or that conformational changes in the capsid during disassembly in the endosome lumen expose a hydrophobic segment of L1 or L2, which can embed in the endosomal membrane and protrude into the cytoplasm where it can bind to the retromer. A transmembrane domain exists in the N terminus of L2 (41), and escape of HPV from the endosome and subsequent transport to the nucleus requires a hydrophobic C-terminal segment of the L2 protein, which can disrupt membranes and target proteins to membranes (21).…”

“…One study concluded that HPV16 traffics through the endoplasmic reticulum (ER) (11). The L2 protein appears to be important for proper intracellular trafficking, as does binding of sorting nexin 17 to an internal segment of L2 (21)(22)(23).…”

The Cytoskeletal Adaptor Obscurin-Like 1 Interacts with the Human Papillomavirus 16 (HPV16) Capsid Protein L2 and Is Required for HPV16 Endocytosis

“…DiGiuseppe and coworkers revealed that L2 amino acid residues 64 to 81 and 163 to 170 and the L2 C-terminal exposure on the cytosolic side of intracellular membranes enable interaction with cytosolic host cell factors (39). Interactions of L2 with actin (40), components of the retrograde transport machinery (37,41,42), sorting nexins 17 and 27, TSG101, ␥-secretase, and Hsc70, as well as the microtubule network, have been reported (37,(41)(42)(43)(44)(45)(46)(47)(48). These interactions result in trafficking to the Golgi network (37,41,42,47), transport toward the nucleus (43,44), and accumulation at nuclear substructures (49)(50)(51)(52)(53).…”

Incoming human papillomavirus type 16 genome resides in a vesicular compartment throughout mitosis

“…Host cell cyclophilins release the majority of L1 from the L2 protein, which remains in complex with the viral genome (2,23,24). A large portion of the L2 protein translocates across the endocytic membrane to engage factors, including the retromer complex, dynein, sorting nexins, and rab GTPases, that mediate transport to the trans-Golgi network (TGN) (25)(26)(27)(28)(29)(30)(31)(32)(33)). An siRNA screen has suggested that nuclear pore complexes are not required for nuclear entry, but that nuclear envelope breakdown during mitosis is necessary (34,35).…”