The Basic Domain of HIV-Tat Transactivating Protein Is Essential for Its Targeting to Lipid Rafts and Regulating Fibroblast Growth Factor-2 Signaling in Podocytes Isolated from Children with HIV-1–Associated Nephropathy

Abstract

Podocyte injury has a critical role in the pathogenesis of HIV-associated nephropathy (HIVAN). The HIV-1 transactivator of transcription (Tat), combined with fibroblast growth factor-2 (FGF-2), can induce the dedifferentiation and proliferation of cultured human podocytes. Cellular internalization of Tat requires interactions with heparan sulfate proteoglycans and cholesterol-enriched lipid rafts (LRs). However, the specific distribution of Tat in human podocytes and its ability to associate with LRs have not been documented. Here, we found that Tat is preferentially recruited to LRs in podocytes isolated from children with HIVAN. Furthermore, we identified arginines in the basic domain (RKKRRQRRR) of Tat as essential for (1) targeting Tat to LRs, (2) Tat-mediated increases in the expression of Rho-A and matrix metalloproteinase-9 in LRs, and (3) Tat-mediated enhancement of FGF-2 signaling in human podocytes and HIV-transgenic mouse kidneys and the exacerbation of renal lesions in these mice. Tat carrying alanine substitutions in the basic domain (AKKAAQAAA) remained localized in the cytosol and did not associate with LRs or enhance FGF-2 signaling in cultured podocytes. These results show the specific association of Tat with LRs in podocytes isolated from children with HIVAN, confirm Tat as a regulator of FGF-2 signaling in LRs, and identify the key domain of Tat responsible for promoting these effects and aggravating renal injury in HIV-transgenic mice. Moreover, these results provide a molecular framework for developing novel therapies to improve the clinical outcome of children with HIVAN.

APOL1-G1 in Nephrocytes Induces Hypertrophy and Accelerates Cell Death

“…In this new animal model, we found that APOL1-G1 cloned from podocytes cultured from a child with HIV-associated nephropathy 40 induced greater cytotoxicity in several tissues, including nephrocytes, when compared with the nonrisk APOL1-G0 allele. Although ubiquitous expression of either APOL1 allele throughout development led to pupa stage lethality, G1 expression caused earlier lethality.…”

“…The APOL1-G1 cDNA was obtained from a cDNA library generated from podocytes cultured from a child with HIV-associated nephropathy. 40 This APOL1-G1 differs from the wild type APOL1-G0 (AAI43040) only at S342 and I384. To generate UAS-APOL1-G0 and UAS-APOL1-G1 constructs, the above cDNAs of APOL1-G0 and G1 alleles were cloned into the pUAST vector and introduced into the germ cells of flies by standard P element-mediated germ line transformation.…”

“…40 Figure 1A shows the domain structure of human APOL1 protein and amino acid changes distinguishing APOL1 encoded by the G0, G1, and G2 alleles. To specify tissue and/or stage specificity of transgene expression we employed the Drosophila UAS-Gal4 system.…”

Exosome-associated release, uptake, and neurotoxicity of HIV-1 Tat protein

“…Unconventional secretion of Tat protein outside the cell has been attributed to Tat interaction with phosphatidylinositol 4, 5-bisphosphate head groups in the phospholipid membranes and with negatively charged lipid groups in the membranes such as dioleoylphosphocholine head groups and lipid raft domains through its positively charged basic domain (Akabori et al 2014; Futaki et al 2001; Rayne et al 2010a; Tyagi et al 2001; Xie et al 2014). Tat has recently been shown to bind endolysosomal membranes resulting in enlarged and dysfunctional lysosomes (Hui et al 2012).…”

Ablation of FGFR2 in Fibroblasts Ameliorates Kidney Fibrosis after Ischemia/Reperfusion Injury in Mice

“…For example, in adult rats, FGF2 treatment caused focal segmental glomerulosclerosis partly via stimulating podocyte mitosis [7,36,37] . Combination of FGF2 with HIV-1 transactivator of transcription could induce the dedifferentiation and proliferation of cultured human podocyte [38] . In addition, administration of FGF7 promoted DNA synthesis in cultured renal proximal tubule epithelial cells [23] .…”