Disease relevance of VPS4A

• Budding of PPxY-containing rhabdoviruses is not dependent on host proteins TGS101 and VPS4A [1].
• Dominant negative mutant Vps4 proteins that inhibit vacuolar protein sorting also arrest HIV-1 and MLV budding [2].
• Potent inhibition of human Hepatitis B virus replication by a host factor Vps4 [3].
• In contrast, wild-type Vps4 at low dose can inhibit HBV replication more effectively in human hepatoblastoma cell line HepG2, than in human hepatoma cell line Huh7 [3].

High impact information on VPS4A

• HIV-1 budding appears to require Vps4 and Tsg101-two proteins that have links to endosomal sorting machinery [4].
• The subsequent dissociation of ESCRT complexes from endosomes requires Vps4, a member of the AAA family of adenosine triphosphatases [5].
• Here, we report the solution structure of the N-terminal VPS4A microtubule interacting and transport (MIT) domain and demonstrate that the VPS4A MIT domain binds the C-terminal half of the ESCRT-III protein, CHMP1B (Kd = 20 +/- 13 microM) [6].
• Finally, a dominant negative mutant of the VPS4 protein was shown to block the enhanced alpha1 microglobulin secretion in ORF3-expressing hepatocytes [7].
• Together with earlier studies, our work suggests that a variety of ESCRT-III-containing polymers can assemble on membranes and recruit SKD1 during formation of the MVB [8].

Biological context of VPS4A

• A BLAST search of the human genome database with the human VPS4A sequence yielded a double match, most likely due to a faulty assembly of sequence contigs in the human draft sequence [9].
• The vacuolar protein sorting defect of vps4 mutant yeast cells was complemented completely by heterologous expressed human VPS4-B protein, and partially by the human VPS4-A protein [10].
• We isolated the mouse SKD1 locus and found that the SKD1 gene is split into 11 exons covering a region of 29kb of the genome [11].
• Analysis of the promoter region, which revealed features common for 'housekeeping genes', is consistent with previous results of a mouse multi-tissue Northern blot, confirming that SKD1 is a ubiquitously expressed gene [11].
• The phenotype described here is largely consistent with the defects in vacuolar sorting associated with class E vps mutants in yeast, and a role for mammalian VPS4 is discussed in this context [12].

Anatomical context of VPS4A

• Sorting of receptors from the early endosome to the recycling compartment or to the trans-Golgi network was not significantly affected, and no mutant hVPS4 associated with these compartments [12].
• To investigate the function of mammalian VPS4 in endosomal trafficking, we have transiently expressed wild-type or ATPase-defective human VPS4 (hVPS4) in cultured cells [12].
• Here, we show that an ATPase-deficient mutant of hVPS4 (hVPS4(EQ)) increases the association of bilayered coats with endosomal vacuoles [13].
• An ATPase-defective Vps4-A mutant, Vps4-A(E228Q), expressed in HeLa cells was accumulated in the early endosomes [14].
• All tested VPS4 fusion proteins were found in the cytosol [9].

Associations of VPS4A with chemical compounds

• Vps4-A associated with both guanosine 5'-[beta-thio]triphosphate-bound active and guanosine 5'-[beta-thio]diphosphate-bound inactive forms of Rnd2 [14].
• SKD1(E235Q) associated with NPC1 on the endosomal membrane, whereas wild-type SKD1 associated with NPC1 only when cells were depleted of cholesterol [15].

Physical interactions of VPS4A

• These results suggest that Rnd2 is involved in the regulation of endosomal trafficking via direct binding to Vps4-A [14].

Other interactions of VPS4A

• 3) Like TGS101, VPS37B became trapped on aberrant endosomal compartments in the presence of VPS4A proteins lacking ATPase activity [16].
• Fluorescent in situ hybridization and radiation hybrid analyses demonstrated that human and mouse VPS4A/a and VPS4B/b are located on syntenic chromosomal regions [9].
• L-domains can functionally interact with cellular proteins involved in vacuolar sorting (VPS4A and TSG101) and endocytic pathways (Nedd4), suggesting involvement of these pathways in virus budding [1].
• Consistent with a role of VPS4A in the budding of both PPPY and PTAP motif-containing viruses, the overexpression of ATPase-defective GFP-VPS4A fusion proteins blocked both wild-type and PSAP mutant virus release [17].

References