HIV-1 Tat Elongates the G1 Phase and Indirectly Promotes HIV-1 Gene Expression in Cells of Glial Origin

Mondira Kundu,Sunita Sharma,Antonio De Luca,Antonio Giordano,Jay Rappaport,Kamel Khalili,Shohreh Amini

doi:10.1074/jbc.273.14.8130

Abstract

Human immunodeficiency virus type-1 (HIV-1) infection of the central nervous system (CNS) gives rise to many of the neurological complications in patients with AIDS. Infection of microglial cells and astrocytes in the brain promotes the release of HIV-1 Tat and other candidate neurotoxins that may be associated with the widespread neuropathology. To examine the contribution of HIV-1 Tat to the interplay between virus and CNS cells, the human astrocytic cell line, U-87MG, was treated with recombinant Tat protein. Fluorescence-activated cell sorting analysis indicated that Tat induces a G1 arrest in these cells. Consistent with this observation, lower levels of cyclin E-Cdk2 kinase activity and phosphorylated Rb were detected in the Tat-treated cells compared with the control cells. Interestingly, our observations indicate that the underphosphorylated form of Rb that is prevalent in Tat-treated cells promotes HIV-1 transcription by a mechanism involving the NF-kappaB enhancer region. Taken together, the data presented here provide the first evidence that the HIV-1 regulatory protein, Tat, may manipulate the host cell cycle to promote viral gene expression. The significance of these findings relates to the current hypothesis that indirect effects of HIV-1 infection of the CNS may contribute to the neurological complications associated with AIDS dementia complex.

Highlights

Neuropathological features of HIV-11 infection include reactive astrogliosis, neuronal loss, widespread myelin pallor, subtle alteration of neocortical dendritic processes, and formation of multinucleated giant cells [1,2,3]
Since Tat can induce the expression of cytokines that can exert positive and negative effects on the growth of astrocytic cells, we decided to examine the effect of Tat on astrocyte proliferation
Fluorescence-activated cell sorting analysis of synchronized U-87MG cells harvested at various intervals after stimulation with 10% serum and 200 ng/ml glutathione S-transferase (GST) revealed that the normal length of the U-87MG cell cycle is approximately 24 h, with the majority of cells at S phase within 20 h (Fig. 1A)

Summary

Introduction

Neuropathological features of HIV-11 infection include reactive astrogliosis, neuronal loss, widespread myelin pallor, subtle alteration of neocortical dendritic processes, and formation of multinucleated giant cells [1,2,3]. Consistent with this observation, lower levels of cyclin E-Cdk2 kinase activity and phosphorylated Rb were detected in the Tat-treated cells compared with the control cells.

Results

Conclusion