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Michael Mashiba
e-mail address: mmashiba@umich.edu

Mentor: Kathleen Collins, MD, PhD

Research Description

Vpr promotes HIV-1 particle production and Env stability in primary human monocyte-derived macrophages

Vpr is a pleiotropic accessory protein encoded by many lentiviruses, including HIV-1. In HIV-1 infected monocyte-derived macrophages (MDM), Vpr enhances virus production and spread.  However, the molecular mechanism for this observation is unknown.   To better understand the role of Vpr during infection of MDM, we have generated a vpr-null mutant virus from the dual tropic molecular clone 89.6.  In agreement with prior studies, we observed that Vpr enhanced the percentage of MDMs that were infected based on intracellular Gag staining.  Vpr expression also increased virus production based on p24 ELISA. In comparison, the effects of Vpr on infection rate and virus production in primary CD4+ T lymphocytes were less dramatic.  We found that the effects of Vpr on MDM infection rate were largely due to enhanced viral spread as this phenotype was abrogated by antiretroviral drugs and by the use of replication-defective 89.6env- mutant.   In addition, we noted that MDM infected with 89.6vpr- had lower cellular levels of Env gp160, gp120 and gp41 than MDM infected with wild-type 89.6.  The effect of Vpr on cellular Env levels was greater than the effect of Vpr on intracellular Gag levels.  89.6vpr- particles produced in MDM also had lower Env levels than wild-type after normalizing for p24, but this phenotype did not affect infectivity of the particles in our system.  Notably, 89.6vpr- particles produced in 293T cells had wild-type levels of Env, suggesting that Vpr’s effect on Env was specific to the MDM cell type.  We are currently investigating the molecular mechanism responsible for the effects of Vpr on virus production and Env levels.


Mashiba M and Collins KL.  Molecular mechanisms of HIV immune evasion of the innate immune response in myeloid cells.  Viruses.  2013 Jan.  5(1):1-14.

Norman JM, Mashiba M, McNamara LA, Onafuwa-Nuga A, Chiari-Fort E, Shen W, Collins KL. The antiviral factor APOBEC3G enhances the recognition of
HIV-infected primary T cells by natural killer cells. Nat Immunol. 2011 Aug 28.
doi: 10.1038/ni.2087.

Miller DL, Rickards B, Mashiba M, Huang W, Flint SJ. The adenoviral E1B 55-kilodalton protein controls expression of immune response genes but not p53-dependent transcription. J Virol. 2009 Apr;83(8):3591-603. Epub 2009 Feb 11.

Takaoka M, Smith CE, Mashiba MK, Okawa T, Andl CD, El-Deiry WS, Nakagawa H.EGF-mediated regulation of IGFBP-3 determines esophageal epithelial cellular response to IGF-I. Am J Physiol Gastrointest Liver Physiol. 2006 Feb;290(2):G404-16. Epub 2005 Oct 6.


M. Mashiba, D. Collins and K. Collins.  “Vpr promotes HIV-1 particle production and Env stability in primary human monocyte-derived macrophages.”  Meeting on Retroviruses, Cold Spring Harbor Laboratory, Cold Spring Harbor, NY.  May 20-25, 2013.

M. Mashiba and K. Collins.  “Investigating the role of HIV-1 Vpr in the infection of macrophages.”  Meeting on Retroviruses, Cold Spring Harbor Laboratory, Cold Spring Harbor, NY.  May 21-26, 2012.

M. Mashiba and K. Collins.  “HIV-1 accessory proteins Vif and Vpr limit restriction by the innate immune response.”  Michigan Medical Scientist Training Program Retreat, Ralph A MacMullen Conference Center, Roscommon, MI.  July 29-31, 2011.


Rackham Conference Travel Grant, University of Michigan, 2013
Rackham Graduate Student Research Grant, University of Michigan, 2012


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