Targeting ABL1 or ARG Tyrosine Kinases to Restrict HIV-1 Infection in Primary CD4+ T-Cells or in Humanized NSG Mice.

BACKGROUND: Previous studies support dasatinib as a potent inhibitor of HIV-1 replication. However, a functional distinction between 2 kinase targets of the drug, ABL1 and ARG, has not been assessed. SETTING: We used primary CD4 T-cells, CD8-depleted peripheral blood mononuclear cells (PBMCs) from a treatment naïve HIV-1 patient, and a humanized mouse model of HIV-1 infection. We assessed the roles of ABL1 and ARG during HIV-1 infection and use of dasatinib as a potential antiviral against HIV-1 in humanized mice. METHODS: Primary CD4 T-cells were administered siRNA targeting ABL1 or ARG, then infected with HIV-1 containing luciferase reporter viruses. Quantitative polymerase chain reaction of viral integration of 4 HIV-1 strains was also assessed. CD8-depleted PBMCs were treated for 3 weeks with dasatinib. NSG mice were engrafted with CD34 pluripotent stem cells from human fetal cord blood, and infected with Ba-L virus after 19 weeks. Mice were treated daily with dasatinib starting 5 weeks after infection. RESULTS: siRNA knockdown of ABL1 or ARG had no effect on viral reverse transcripts, but increased 2-LTR circles 2- to 4-fold and reduced viral integration 2- to 12-fold. siRNA knockdown of ARG increased SAMHD1 activation, whereas knockdown of either kinase reduced RNA polymerase II activation. Treating CD8-depleted PBMCs from a treatment-naïve patient with 50 nM of dasatinib for 3 weeks reduced p24 levels by 99.8%. Ba-L (R5)-infected mice injected daily with dasatinib showed a 95.1% reduction in plasma viral load after 2 weeks of treatment. CONCLUSIONS: We demonstrate a novel nuclear role for ABL1 and ARG in ex vivo infection experiments, and proof-of-principle use of dasatinib in a humanized mouse model of HIV-1 infection.

Endoplasmic Reticulum-Targeted Subunit Toxins Provide a New Approach to Rescue Misfolded Mutant Proteins and Revert Cell Models of Genetic Diseases.

Many germ line diseases stem from a relatively minor disturbance in mutant protein endoplasmic reticulum (ER) 3D assembly. Chaperones are recruited which, on failure to correct folding, sort the mutant for retrotranslocation and cytosolic proteasomal degradation (ER-associated degradation-ERAD), to initiate/exacerbate deficiency-disease symptoms. Several bacterial (and plant) subunit toxins, retrograde transport to the ER after initial cell surface receptor binding/internalization. The A subunit has evolved to mimic a misfolded protein and hijack the ERAD membrane translocon (dislocon), to effect cytosolic access and cytopathology. We show such toxins compete for ERAD to rescue endogenous misfolded proteins. Cholera toxin or verotoxin (Shiga toxin) containing genetically inactivated (± an N-terminal polyleucine tail) A subunit can, within 2-4 hrs, temporarily increase F508delCFTR protein, the major cystic fibrosis (CF) mutant (5-10x), F508delCFTR Golgi maturation (<10x), cell surface expression (20x) and chloride transport (2x) in F508del CFTR transfected cells and patient-derived F508delCFTR bronchiolar epithelia, without apparent cytopathology. These toxoids also increase glucocerobrosidase (GCC) in N370SGCC Gaucher Disease fibroblasts (3x), another ERAD-exacerbated misfiling disease. We identify a new, potentially benign approach to the treatment of certain genetic protein misfolding diseases.

Synthesis of a novel photoactivatable glucosylceramide cross-linker.

The biosynthesis of glucosylceramide (GlcCer) is a key rate-limiting step in complex glycosphingolipid (GSL) biosynthesis. To further define interacting partners of GlcCer, we have made a cleavable, biotinylated, photoreactive GlcCer analog in which the reactive nitrene is closely apposed to the GlcCer head group, by substituting the native fatty acid with d, l-2-aminohexadecanoic acid. Two amino-GlcCer diastereomer cross-linkers (XLA and XLB) were generated. XLB proved an effective lactosylceramide (LacCer) synthase substrate while XLA was inhibitory. Both probes specifically bound and cross-linked the GlcCer binding protein, glycolipid transfer protein (GLTP), but not other GSL binding proteins (Shiga toxin and cholera toxin). GlcCer inhibited GLTP cross-linking. Both GlcCer cross-linkers competed with microsomal nitrobenzoxadiazole (NBD)-GlcCer anabolism to NBD-LacCer. GLTP showed marked, ATP-dependent enhancement of cell-free intact microsomal LacCer synthesis from endogenous or exogenous liposomal GlcCer, supporting a role in the transport/membrane translocation of cytosolic and extra-Golgi GlcCer. GLTP was specifically labeled by either XLA or XLB GlcCer cross-linker during this process, together with a (the same) small subset of microsomal proteins. These cross-linkers will serve to probe physiologically relevant GlcCer-interacting cellular proteins.

Inhibition of Rab prenylation by statins induces cellular glycosphingolipid remodeling.

Statins, which specifically inhibit HMG Co-A reductase, the rate-limiting step of cholesterol biosynthesis, are widely prescribed to reduce serum cholesterol and cardiac risk, but many other effects are seen. We now show an effect of these drugs to induce profound changes in the step-wise synthesis of glycosphingolipids (GSLs) in the Golgi. Glucosylceramide (GlcCer) was increased several-fold in all cell lines tested, demonstrating a widespread effect. Additionally, de novo or elevated lactotriaosylceramide (Lc3Cer; GlcNAcß1-3Galß1-4GlcCer) synthesis was observed in 70%. Western blot showed that GlcCer synthase (GCS) was elevated by statins, and GCS and Lc3Cer synthase (Lc3S) activities were increased; however, transcript was elevated for Lc3S only. Supplementation with the isoprenoid precursor, geranylgeranyl pyrophosphate (GGPP), a downstream product of HMG Co-A reductase, reversed statin-induced glycosyltransferase and GSL elevation. The Rab geranylgeranyl transferase inhibitor 3-PEHPC, but not specific inhibitors of farnesyl transferase, or geranylgeranyl transferase I, was sufficient to replicate statin-induced GlcCer and Lc3Cer synthesis, supporting a Rab prenylation-dependent mechanism. While total cholesterol was unaffected, the trans-Golgi network (TGN) cholesterol pool was dissipated and medial Golgi GCS partially relocated by statins. GSL-dependent vesicular retrograde transport of Verotoxin and cholera toxin to the Golgi/endoplasmic reticulum were blocked after statin or 3-PEHPC treatment, suggesting aberrant, prenylation-dependent vesicular traffic as a basis of glycosyltransferase increase and GSL remodeling. These in vitro studies indicate a previously unreported link between Rab prenylation and regulation of GCS activity and GlcCer metabolism.

Cholesterol masks membrane glycosphingolipid tumor-associated antigens to reduce their immunodetection in human cancer biopsies.

Glycosphingolipids (GSLs) are neoplastic and normal/cancer stem cell markers and GSL/cholesterol-containing membrane rafts are increased in cancer cell plasma membranes. We define a novel means by which cancer cells can restrict tumor-associated GSL immunoreactivity. The GSL-cholesterol complex reorients GSL carbohydrate to a membrane parallel, rather than perpendicular conformation, largely unavailable for antibody recognition. Methyl-ß-cyclodextrin cholesterol extraction of all primary human tumor frozen sections tested (ovarian, testicular, neuroblastoma, prostate, breast, colon, pheochromocytoma and ganglioneuroma), unmasked previously "invisible" membrane GSLs for immunodetection. In ovarian carcinoma, globotriaosyl ceramide (Gb3), the GSL receptor for the antineoplastic Escherichia coli-derived verotoxin, was increased throughout the tumor. In colon carcinoma, Gb3 detection was vastly increased within the neovasculature and perivascular stroma. In tumors considered Gb3 negative (neuroblastoma, Leydig testicular tumor and pheochromocytoma), neovascular Gb3 was unmasked. Tumor-associated GSL stage-specific embryonic antigen (SSEA)-1, SSEA-3, SSEA-4 and globoH were unmasked according to tumor: SSEA-1 in prostate/colon; SSEA-3 in prostate; SSEA-4 in pheochromocytoma/some colon tumors; globoH in prostate/some colon tumors. In colon, anti-SSEA-1 was tumor cell specific. Within the GSL-cholesterol complex, filipin-cholesterol binding was also reduced. These results may relate to the ill-defined benefit of statins on cancer prognosis, for example, prostate carcinoma. We found novel anti-tumor GSL antibodies circulating in 3/5 statin-treated, but not untreated, prostate cancer patients. Lowering tumor membrane cholesterol may permit immune recognition of otherwise unavailable tumor-associated GSL carbohydrate, for more effective immunosurveillance and active/passive immunotherapy. Our results show standard immunodetection of tumor GSLs significantly under assesses tumor membrane GSL content, impinging on the current use of such antigens as cancer vaccines.

Comparison of detection methods for cell surface globotriaosylceramide.

The cell surface-expressed glycosphingolipid (GSL), globotriaosylceramide (Gb(3)), is becoming increasingly important and is widely studied in the areas of verotoxin (VT)-mediated cytotoxicity, human immunodeficiency virus (HIV) infection, immunology and cancer. However, despite its diverse roles and implications, an optimized detection method for cell surface Gb(3) has not been determined. GSLs are differentially organized in the plasma membrane which can affect their availability for protein binding. To examine various detection methods for cell surface Gb(3), we compared four reagents for use in flow cytometry analysis. A natural ligand (VT1B) and three different monoclonal antibodies (mAbs) were optimized and tested on various human cell lines for Gb(3) detection. A differential detection pattern of cell surface Gb(3) expression, which was influenced by the choice of reagent, was observed. Two mAb were found to be suboptimal. However, two other methods were found to be useful as defined by their high percentage of positivity and mean fluorescence intensity (MFI) values. Rat IgM anti-Gb(3) mAb (clone 38-13) using phycoerythrin-conjugated secondary antibody was found to be the most specific detection method while the use of VT1B conjugated to Alexa488 fluorochrome was found to be the most sensitive; showing a rare crossreactivity only when Gb(4) expression was highly elevated. The findings of this study demonstrate the variability in detection of Gb(3) depending on the reagent and cell target used and emphasize the importance of selecting an optimal methodology in studies for the detection of cell surface expression of Gb(3).

Induction of HIV-1 resistance: cell susceptibility to infection is an inverse function of globotriaosyl ceramide levels.

To examine the role of the glycosphingolipid (GSL), globotriaosylceramide (Gb(3), CD77, p(k) blood group antigen) in HIV-1 infection, we have pharmacologically modulated Gb(3) metabolism in an X4 HIV-1 infectable monocytic cell line (THP-1) that naturally expresses Gb(3) and in a Gb(3)-expressing glioblastoma cell line (U87) transfected to express both CD4 and CCR5 to permit R5 HIV-1 infection. THP-1 and U87 cells were treated with either a competitive inhibitor of alpha-galactosidase A, 1-deoxygalactonojirimycin (DGJ) to induce Gb(3) accumulation, or a glucosylceramide synthase inhibitor, phenyl-2-palmitylamino-3-pyrrolidino-1-propanol (P4) to deplete cells of Gb(3). HIV susceptibility was determined via measurement of p24(gag) antigen production by ELISA. In addition, total cellular Gb(3) content was determined using thin layer chromatography followed by Verotoxin1 overlay binding. The cell surface expression of Gb(3) was verified by FACS analysis. We found that DGJ significantly decreased THP-1 and U87 cell susceptibility to HIV-1(IIIB) and HIV-1(BaL) infection, respectively, at a concentration of approximately 100 microM. In contrast, P4 (2 microM) substantially increased cellular susceptibility to HIV-1 infection. Total cellular GSL analysis verified increased Gb(3) expression in cells treated with DGJ and considerable reduction of Gb(3) in P4-treated cells as compared to controls. These results show a reciprocal relationship between Gb(3) expression and infection with either X4 HIV-1(IIIB) or R5 HIV-1(Ba-L). These results support previous studies that Gb(3) provides resistance to HIV infection. Variable Gb(3) expression may provide a natural HIV resistance factor in the general population, and pharmacological manipulation of Gb(3) levels may provide an approach to induction of HIV resistance.

Treatment of neutral glycosphingolipid lysosomal storage diseases via inhibition of the ABC drug transporter, MDR1. Cyclosporin A can lower serum and liver globotriaosyl ceramide levels in the Fabry mouse model.

We have shown that the ABC transporter, multiple drug resistance protein 1 (MDR1, P-glycoprotein) translocates glucosyl ceramide from the cytosolic to the luminal Golgi surface for neutral, but not acidic, glycosphingolipid (GSL) synthesis. Here we show that the MDR1 inhibitor, cyclosporin A (CsA) can deplete Gaucher lymphoid cell lines of accumulated glucosyl ceramide and Fabry cell lines of globotriaosyl ceramide (Gb3), by preventing de novo synthesis. In the Fabry mouse model, Gb3 is increased in the heart, liver, spleen, brain and kidney. The lack of renal glomerular Gb3 is retained, but the number of verotoxin 1 (VT1)-staining renal tubules, and VT1 tubular targeting in vivo, is markedly increased in Fabry mice. Adult Fabry mice were treated with alpha-galactosidase (enzyme-replacement therapy, ERT) to eliminate serum Gb3 and lower Gb3 levels in some tissues. Serum Gb3 was monitored using a VT1 ELISA during a post-ERT recovery phase +/- biweekly intra peritoneal CsA. After 9 weeks, tissue Gb3 content and localization were determined using VT1/TLC overlay and histochemistry. Serum Gb3 recovered to lower levels after CsA treatment. Gb3 was undetected in wild-type liver, and the levels of Gb3 (but not gangliosides) in Fabry mouse liver were significantly depleted by CsA treatment. VT1 liver histochemistry showed Gb3 accumulated in Kupffer cells, endothelial cell subsets within the central and portal vein and within the portal triad. Hepatic venule endothelial and Kupffer cell VT1 staining was considerably reduced by in vivo CsA treatment. We conclude that MDR1 inhibition warrants consideration as a novel adjunct treatment for neutral GSL storage diseases.