Identification of a Region within the Cytoplasmic Domain of the Subtype B Vpu Protein of Human Immunodeficiency Virus Type 1 (HIV-1) That Is Responsible for Retention in the Golgi Complex and Its Absence in the Vpu Protein from a Subtype C HIV-1.

E Pacyniak — 2005-06-03T15:46:48-00:00

AIDS Res Hum Retroviruses, Vol. 21, No. 5. (May 2005), pp. 379-394.

The structure of the Vpu protein of human immunodeficiency virus type 1 (HIV-1) is composed of a short Nterminal domain (NTD), a transmembrane domain (TM), and a cytoplasmic domain (CD). Previous studies have shown that the Vpu protein from subtype B HIV-1 is transported predominantly to the rough endoplasmic reticulum (RER)/Golgi complex compartments of the cell and is not incorporated into virions. Using a previously described VpuEGFP reporter system in which the Vpu protein was fused to the gene for enhanced green fluorescent protein (EGFP), we showed that the subtype B Vpu fusion protein was localized to the RER/Golgi region of the cell, similar to the native protein. In the present study, we show that fusion of the subtype C Vpu to EGFP results in a fusion protein that is transported to the cell surface. Using this reporter system, chimeric Vpu proteins in which the CD of the subtype B and C proteins were exchanged showed that the CD was sufficient for targeting the subtype B protein to the Golgi complex of the cell. Following identification of the cytoplasmic domain as being responsible for intracellular targeting, we then generated a series of mutants in which 13, 23, 31, 38, 51, and 56 amino acids were deleted from the cytoplasmic domain of subtype B Vpu. These deletion mutants were analyzed by SDS-PAGE for size, for membrane localization, and intracellular localization by confocal fluorescence microscopy. Our results indicate that the mutant with the carboxyl-terminal 13 amino acids deleted was still localized to the Golgi complex but mutants with 23, 31, 38, 51, and 56 amino acids from the carboxyl-terminus of the subtype B Vpu were transported to the cell surface. These results suggest that a signal for the retention of the subtype B Vpu within the Golgi complex resides in the second alpha-helical domain.

Vpu-mediated CD4 down-regulation and degradation is conserved among highly divergent SIV(cpz) strains.

LM Gomez — 2007-08-02T22:28:08-00:00

Virology, Vol. 335, No. 1. (25 April 2005), pp. 46-60.

Human immunodeficiency virus type 1 (HIV-1) along with simian immunodeficiency viruses from chimpanzees (SIV(cpz)) and three species of Old World monkeys from the genus Cercopithecus have been shown to encode a Vpu protein. To date, the functional characterization of Vpu has been limited to a small number of subtype B and more recently subtype C Vpu proteins. Using a recently developed VpuEGFP reporter system, we have shown that the subtype B and C Vpus are capable of preventing CD4 from being expressed on the cell surface. Using the same reporter system, we report here on the expression and functional analysis of Vpu protein from four SIV(cpz) isolates (CAM13, ANT, TAN1, and GAB1). All four SIV Vpu fusion proteins were efficiently expressed and prevented CD4 expression on the cell surface and induced CD4 degradation. This was surprising as three of the SIV(cpz) Vpu fusion proteins had only one canonical casein kinase II (CK-II) site (CAM13, ANT, TAN1) while previous studies with laboratory adapted HXB2 had indicated that both CK-II sites were required for CD4 degradation. Both ANT and TAN1 Vpu sequences encoded five consecutive negatively charged amino acids residues following the only CKII site (SAIEEDEE for ANT; SGVEEDEE for TAN1). We thus explored the possibility that this stretch of negatively charged amino acids might substitute for the lack of second CK-II site. Substitution of the aspartic acid at position 61 and glutamic acid at position 63 in the SIV(cpz) ANT Vpu within with lysine residues abolished the ability of this protein to down-modulate cell surface expression of CD4. Similarly, change of a serine to an alanine residue following the single consensus CK-II site of the CAM13 Vpu (SGNESDGGEEE) abolished CD4-down-regulation, suggesting that this serine was phosphorylated in the absence of a canonical CK-II site. Our results indicate that the serine was required, suggesting that this serine was phosphorylated by CK-II or possibly another cellular kinase. Taken together, these results show for the first time that Vpu proteins from SIV(cpz) isolates, although quite diverse in sequence and predicted secondary structure from the HIV-1 subtype B protein, are capable of down-regulating CD4, which is one of the major functions of the HIV-1 protein.

CiteULike: matzke Hout

Identification of a Region within the Cytoplasmic Domain of the Subtype B Vpu Protein of Human Immunodeficiency Virus Type 1 (HIV-1) That Is Responsible for Retention in the Golgi Complex and Its Absence in the Vpu Protein from a Subtype C HIV-1.

Vpu-mediated CD4 down-regulation and degradation is conserved among highly divergent SIV(cpz) strains.