Human immunodeficiency virus type 1 VPU protein affects Sindbis virus glycoprotein processing and enhances membrane permeabilization.

The human immunodeficiency virus type 1 (HIV-1) Vpu is an integral membrane protein that forms oligomeric structures in membranes. Expression of vpu using Sindbis virus (SV) as a vector leads to permeabilization of plasma membrane to hydrophilic molecules and impaired maturation of wild type SV glycoproteins in BHK cells. The 6K protein is a membrane protein encoded in the SV genome that facilitates budding of virus particles and regulates transport of viral glycoproteins through the secretory pathway. Some of these functions were assayed with a SV mutant containing a partially deleted 6K gene. Transfection of BHK cells with pSVDelta6K vector rendered defective SVDelta6K virus, which had lower membrane permeabilization, impaired glycoprotein processing, and deficient virion budding. Replacement of 6K function by HIV-1 Vpu in SVDelta6K was tested by cloning the vpu gene under a duplicated late promoter (pSVDelta6KVpu). The presence of the vpu gene in the 6K-deleted virus enhances membrane permeability, modifies glycoprotein precursor processing, and facilitates infectious virus particle production. Restoration of infectivity of 6K-deleted SV by Vpu was evidenced by increased PFU production and cytopathic effect on infected cells. The modification of SVDelta6K glycoprotein maturation by Vpu was reflected in augmented processing of B precursor and impairment of PE2 cleavage. Taken together, our data support the notion that HIV-1 Vpu and SV 6K proteins share some analogous functions.