title: The chemokine receptor CXCR4 regulates cell-cycle proteins in neurons.
abstract: Neurons express a variety of chemokine receptors that regulate neuronal signaling and survival, including CXCR4 and CCR5, the two major human immunodeficiency virus (HIV) coreceptors. However, the role of chemokine receptors in HIV neuropathology and neuroinflammatory disorders is still unclear. This study aims to determine whether chemokine receptors regulate the activity of cell-cycle proteins in neurons and evaluate the possibility that alterations of these proteins are involved in HIV neuropathogenesis. The authors studied the effect of the chemokine stromal cell-derived factor (SDF)-1alpha, the natural CXCR4 ligand, and an X4-using variant of gp120 on the activity of cell-cycle proteins involved in neuronal apoptosis and differentiation, such as Rb and E2F-1. Changes in expression, localization, and phosphorylation/activation of Rb and E2F-1 induced by SDF-1alpha (20 nM) gp120(IIIB) (200 pM) were analyzed in primary cultures of rat neurons and in a human cell line expressing recombinant CXCR4. The data indicate that changes in the nuclear and cytosolic levels of Rb--which result in the functional loss of this protein--are associated with apoptosis in hippocampal or cerebellar granule neurons and in cell lines. SDF-1alpha, which is able to rescue these neurons from apoptosis, induces a time-dependent increase of total Rb expression while decreasing the nuclear content of phosphorylated (Ser780/Ser795) Rb and the transcriptional activity of E2F-1. The HIV envelope protein gp120(IIIB) exerts opposite effects at the nuclear level. These data indicate that CXCR4 affects cell-cycle proteins in neurons and raise the possibility that chemokines may contribute to neuronal survival by repressing the activity of E2F-dependent apoptotic genes and maintaining neurons in a highly differentiated and quiescent state. This state may be altered during neuroinflammatory conditions and/or by HIV-derived proteins.
authors.affiliation: Department of Pharmacology and Physiology, Drexel University College of Medicine, Philadelphia, Pennsylvania 19102, USA.
authors.forename: Muhammad Zafrullah
authors.initials: MZ
authors.lastname: Khan
authors.forename: Renato
authors.initials: R
authors.lastname: Brandimarti
authors.forename: Brian Joseph
authors.initials: BJ
authors.lastname: Musser
authors.forename: Danielle Marie
authors.initials: DM
authors.lastname: Resue
authors.forename: Alessandro
authors.initials: A
authors.lastname: Fatatis
authors.forename: Olimpia
authors.initials: O
authors.lastname: Meucci
mesh_terms: D000818:Animals; D017209:Apoptosis / Q000187:drug effects; D018797:Cell Cycle Proteins / Q000378:metabolism*; D002454:Cell Differentiation / Q000187:drug effects; D002460:Cell Line; D002467:Cell Nucleus / Q000378:metabolism; D002531:Cerebellum / Q000166:cytology; D054377:Chemokine CXCL12; D019743:Chemokines, CXC / Q000494:pharmacology* / Q000502:physiology; D003513:Cycloheximide / Q000494:pharmacology; D004268:DNA-Binding Proteins; D050684:E2F Transcription Factors; D050687:E2F1 Transcription Factor; D015699:HIV Envelope Protein gp120 / Q000494:pharmacology; D006624:Hippocampus / Q000166:cytology; D006801:Humans; D009419:Nerve Tissue Proteins / Q000378:metabolism*; D009474:Neurons / Q000378:metabolism*; D010766:Phosphorylation / Q000187:drug effects; D011499:Protein Processing, Post-Translational / Q000187:drug effects; D011500:Protein Synthesis Inhibitors / Q000494:pharmacology; D051381:Rats; D019718:Receptors, CXCR4 / Q000187:drug effects / Q000235:genetics / Q000502:physiology*; D011993:Recombinant Fusion Proteins / Q000502:physiology; D016160:Retinoblastoma Protein / Q000378:metabolism; D015398:Signal Transduction; D014157:Transcription Factors / Q000378:metabolism; D014162:Transfection
chemical_list: C515255:CXCL12 protein, human; D018797:Cell Cycle Proteins; D054377:Chemokine CXCL12; D019743:Chemokines, CXC; D004268:DNA-Binding Proteins; D050684:E2F Transcription Factors; D050687:E2F1 Transcription Factor; C493753:E2F1 protein, human; C493755:E2f1 protein, rat; D015699:HIV Envelope Protein gp120; D009419:Nerve Tissue Proteins; D011500:Protein Synthesis Inhibitors; D019718:Receptors, CXCR4; D011993:Recombinant Fusion Proteins; D016160:Retinoblastoma Protein; D014157:Transcription Factors; D003513:Cycloheximide