Osteopontin enhances HIV replication and is increased in the brain and cerebrospinal fluid of HIV-infected individuals.

Department of Neurology, Johns Hopkins University School of Medicine, Baltimore, MD 21287-7131, USA.
Journal of NeuroVirology (Impact Factor: 3.32). 05/2011; 17(4):382-92. DOI: 10.1007/s13365-011-0035-4
Source: PubMed

ABSTRACT Despite effective and widely available suppressive anti-HIV therapy, the prevalence of mild neurocognitive dysfunction continues to increase. HIV-associated neurocognitive disorder (HAND) is a multifactorial disease with sustained central nervous system inflammation and immune activation as prominent features. Inflammatory macrophages, HIV-infected and uninfected, play a central role in the development of HIV dementia. There is a critical need to identify biomarkers and to better understand the molecular mechanisms leading to cognitive dysfunction in HAND. In this regard, we identified through a subtractive hybridization strategy osteopontin (OPN, SPP1, gene) an inflammatory marker, as an upregulated gene in HIV-infected primary human monocyte-derived macrophages. Knockdown of OPN in primary macrophages resulted in a threefold decrease in HIV-1 replication. Ectopic expression of OPN in the TZM-bl cell line significantly enhanced HIV infectivity and replication. A significant increase in the degradation of the NF-κB inhibitor, IκBα and an increase in the nuclear-to-cytoplasmic ratio of NF-κB were found in HIV-infected cells expressing OPN compared to controls. Moreover, mutation of the NF-κB binding domain in the HIV-LTR abrogated enhanced promoter activity stimulated by OPN. Interestingly, compared to cerebrospinal fluid from normal and multiple sclerosis controls, OPN levels were significantly higher in HIV-infected individuals both with and without neurocognitive disorder. OPN levels were highest in HIV-infected individuals with moderate to severe cognitive impairment. Moreover, OPN was significantly elevated in brain tissue from HIV-infected individuals with cognitive disorder versus those without impairment. Collectively, these data suggest that OPN stimulates HIV-1 replication and that high levels of OPN are present in the CNS compartment of HIV-infected individuals, reflecting ongoing inflammatory processes at this site despite anti-HIV therapy.

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    ABSTRACT: Osteopontin (OPN) is a secreted phosphoprotein, originally characterized in malignant-transformed epithelial cells. OPN is associated with tumor metastasis of several tumors and overexpressed in hepatocellular carcinoma (HCC) tissue involving HCC invasion and metastasis. Importantly, OPN is significantly upregulated in liver injury, inflammation and hepatitis C virus (HCV)-associated HCC. However, the underlying mechanisms of OPN activation and its role in HCV-mediated liver disease pathogenesis are not known. In this study, we investigated the mechanism of OPN activation in HCV-infected cells. We demonstrate that HCV-mediated Ca+2 signaling, elevation of reactive oxygen species (ROS), and activation of cellular kinases such as p38 MAPK, JNK, PI3K and MEK1/2 are involved in OPN activation. Incubation of HCV-infected cells with the inhibitors of AP-1 and Sp1, and site-directed mutagenesis of AP-1 and Sp1 binding sites on OPN promoter suggest the critical role of AP-1 and Sp1 in OPN promoter activation. In addition, we show the in vivo interactions of AP-1 and Sp1 with OPN promoter using chromatin immunoprecipitation (ChIP) assay. We also show the calpain mediated processing of precursor OPN (~75 kDa) into ~55 kDa, ~42 kDa and ~36 kDa forms of OPN in HCV-infected cells. Furthermore, we demonstrate the critical role of HCV-induced OPN in increased phosphorylation of Akt, GSK-3β followed by the activation of β-catenin, which can lead to EMT of hepatocytes. Taken together, these studies provide an insight into the mechanisms of OPN activation which is relevant to the metastasis of HCV-associated HCC.
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