Expression of human liver HSPGs on acute myeloid leukemia. Clin Immunol. 2007;122:194-206. [PMID: 17035092 DOI: 10.1016/j.clim.2006.08.017]

Characterization of a new monoclonal anti-glypican-3 antibody specific to the hepatocellular carcinoma cell line, HepG2

AIM

To characterize the antigen on HepG2 cell that is specifically recognized by a new monoclonal antibody raised against human liver heparan sulfate proteoglycan (HSPG), clone 1E4-1D9.

METHODS

The antigen recognized by mAb 1E4-1D9 was immunoprecipitated and its amino acid sequence was analyzed LC/MS. The transmembrane domain, number of cysteine residues, and glycosylation sites were predicted from these entire sequences. Data from amino acid analysis was aligned with glypican-3 (https://www.ebi.ac.uk/Tools/msa/clustalo/). The competitive reaction of mAb 1E4-1D9 and anti-glypican-3 on HepG2 cells was demonstrated by indirect immunofluorescence and analyzed by flow cytometry. Moreover, co-immunoprecipitation of mAb 1E4-1D9 and anti-glypican-3 was performed in HepG2 cells by Western immunoblotting. The recognition by mAb 1E4-1D9 of a specific epitope on solid tumor and hematopoietic cell lines was studied using indirect immunofluorescence and analyzed by flow cytometry.

RESULTS

Monoclonal antibody 1E4-1D9 reacted with an HSPG isolated from human liver and a band of 67 kD was detected under both reducing and non-reducing conditions. The specific antigen pulled down by mAb 1E4-1D9, having a MW of 135 kD, was analyzed. The results showed two sequences of interest, gi30722350 (1478 amino acid) and gi60219551 (1378 amino acid). In both sequences no transmembrane regions were observed. Sequence number gi30722350 was 99.7% showed a match to FYCO1, a molecule involved in induction of autophagy. Sequence number gi60219551 contained 15 cysteines and 11 putative glycosylation sites with 6 predicted N-glycosylation sites. It was also matched with all PDZ domain proteins. Moreover, it showed an 85.7% match to glypican-3. Glypican-3 on HepG2 cells competitively reacted with both phycoerythrin-conjugated anti-glypican-3 and mAb 1E4-1C2 and resulted in an increase of double-stained cell population when higher concentration of mAb 1E4-1D9 was used. Moreover, antigens precipitated from HepG2 cell by anti-glypican-3 could be detected by mAb 1E4-1D9 and vice versa. The recognition of antigens, on other solid tumor cell lines, by mAb 1E4-1D9 was studied. The results demonstrated that mAb 1E4-1D9 reacted with Huh7, HepG2, HT29, MCF7, SW620, Caco2, B16F1, U937, K562 and Molt4 cells. It was also found to be weakly positive to SW1353 and HL60 and negative to H460 and Hela cell lines.

CONCLUSION

All findings show that mAb 1E4-1D9 specifically recognizes glypican-3. Moreover, a new partner molecule of glypican-3, FYCO1 is proposed based on the results from co-precipitation studies.

Transduction of Recombinant M3-p53-R12 Protein Enhances Human Leukemia Cell Apoptosis

Tumor suppressor protein p53 plays important roles in initiating cell cycle arrest and promoting tumor cell apoptosis. Previous studies have shown that p53 is either mutated or defective in approximately 50% of human cancers; therefore restoring normal p53 activity in cancer cells might be an effective anticancer therapeutic approach. Herein, we designed a chimeric p53 protein flanked with the MyoD N-terminal transcriptional activation domain (amino acids 1-62, called M3) and a poly-arginine (R12) cell penetrating signal in its N-and C-termini respectively. This chimeric protein, M3-p53-R12, can be expressed in E. coli and purified using immobilized metal ion chromatography followed by serial refolding dialysis. The purified M3-p53-R12 protein retains DNA-binding activity and gains of cell penetrating ability. Using MTT assay, we demonstrated that M3-p53-R12 inhibited the growth of K562, Jurkat as well as HL-60 leukemia cells carrying mutant p53 genes. Results from FACS analysis also demonstrated that transduction of M3-p53-R12 protein induced cell cycle arrest of these leukemia cells. Of special note, M3-p53-R12 has no apoptotic effect on normal mesenchymal stem cells (MSC) and leukocytes, highlighting its differential effects on normal and tumor cells. To sum up, our results reveal that purified recombinant M3-p53-R12 protein has functions of suppressing the leukemia cell lines' proliferation and launching cell apoptosis, suggesting the feasibility of using M3-p53-R12 protein as an anticancer drug. In the future we will test whether this chimeric protein can preferentially trigger the death of malignant cancer cells without affecting normal cells in animals carrying endogenous or xenographic tumors.

HIV-1 entry in SupT1-R5, CEM-ss, and primary CD4+ T cells occurs at the plasma membrane and does not require endocytosis

Cytoplasmic entry of HIV-1 requires binding of the viral glycoproteins to the cellular receptor and coreceptor, leading to fusion of viral and cellular membranes. Early studies suggested that productive HIV-1 infection occurs by direct fusion at the plasma membrane. Endocytotic uptake of HIV-1 was frequently observed but was considered to constitute an unspecific dead-end pathway. More recent evidence suggested that endocytosis contributes to productive HIV-1 entry and may even represent the predominant or exclusive route of infection. We have analyzed HIV-1 binding, endocytosis, cytoplasmic entry, and infection in T-cell lines and in primary CD4(+) T cells. Efficient cell binding and endocytosis required viral glycoproteins and CD4, but not the coreceptor. The contribution of endocytosis to cytoplasmic entry and infection was assessed by two strategies: (i) expression of dominant negative dynamin-2 was measured and was found to efficiently block HIV-1 endocytosis but to not affect fusion or productive infection. (ii) Making use of the fact that HIV-1 fusion is blocked at temperatures below 23 °C, cells were incubated with HIV-1 at 22 °C for various times, and endocytosis was quantified by parallel analysis of transferrin and fluorescent HIV-1 uptake. Subsequently, entry at the plasma membrane was blocked by high concentrations of the peptidic fusion inhibitor T-20, which does not reach previously endocytosed particles. HIV-1 infection was scored after cells were shifted to 37 °C in the presence of T-20. These experiments revealed that productive HIV-1 entry occurs predominantly at the plasma membrane in SupT1-R5, CEM-ss, and primary CD4(+) T cells, with little, if any, contribution coming from endocytosed virions.

IMPORTANCE

HIV-1, like all enveloped viruses, reaches the cytoplasm by fusion of the viral and cellular membranes. Many viruses enter the cytoplasm by endosomal uptake and fusion from the endosome, while cell entry can also occur by direct fusion at the plasma membrane in some cases. Conflicting evidence regarding the site of HIV-1 fusion has been reported, with some studies claiming that fusion occurs predominantly at the plasma membrane, while others have suggested predominant or even exclusive fusion from the endosome. We have revisited HIV-1 entry using a T-cell line that exhibits HIV-1 endocytosis dependent on the viral glycoproteins and the cellular CD4 receptor; results with this cell line were confirmed for another T-cell line and primary CD4(+) T cells. Our studies show that fusion and productive entry occur predominantly at the plasma membrane, and we conclude that endocytosis is dispensable for HIV-1 infectivity in these T-cell lines and in primary CD4(+) T cells.

Interference with RUNX1/ETO leukemogenic function by cell-penetrating peptides targeting the NHR2 oligomerization domain

The leukemia-associated fusion protein RUNX1/ETO is generated by the chromosomal translocation t(8;21) which appears in about 12% of all de novo acute myeloid leukemias (AMLs). Essential for the oncogenic potential of RUNX1/ETO is the oligomerization of the chimeric fusion protein through the nervy homology region 2 (NHR2) within ETO. In previous studies, we have shown that the intracellular expression of peptides containing the NHR2 domain inhibits RUNX1/ETO oligomerization, thereby preventing cell proliferation and inducing differentiation of RUNX1/ETO transformed cells. Here, we show that introduction of a recombinant TAT-NHR2 fusion polypeptide into the RUNX1/ETO growth-dependent myeloid cell line Kasumi-1 results in decreased cell proliferation and increased numbers of apoptotic cells. This effect was highly specific and mediated by binding the TAT-NHR2 peptide to ETO sequences, as TAT-polypeptides containing the oligomerization domain of BCR did not affect cell proliferation or apoptosis in Kasumi-1 cells. Thus, the selective interference with NHR2-mediated oligomerization by peptides represents a challenging but promising strategy for the inhibition of the leukemogenic potential of RUNX1/ETO in t(8;21)-positive leukemia.

A pH-sensitive heparin-binding sequence from Baculovirus gp64 protein is important for binding to mammalian cells but not to Sf9 insect cells

Binding to heparan sulfate is essential for baculovirus transduction of mammalian cells. Our previous study shows that gp64, the major glycoprotein on the virus surface, binds to heparin in a pH-dependent way, with a stronger binding at pH 6.2 than at 7.4. Using fluorescently labeled peptides, we mapped the pH-dependent heparin-binding sequence of gp64 to a 22-amino-acid region between residues 271 and 292. Binding of this region to the cell surface was also pH dependent, and peptides containing this sequence could efficiently inhibit baculovirus transduction of mammalian cells at pH 6.2. When the heparin-binding peptide was immobilized onto the bead surface to mimic the high local concentration of gp64 on the virus surface, the peptide-coated magnetic beads could efficiently pull down cells expressing heparan sulfate but not cells pretreated with heparinase or cells not expressing heparan sulfate. Interestingly, although this heparin-binding function is essential for baculovirus transduction of mammalian cells, it is dispensable for infection of Sf9 insect cells. Virus infectivity on Sf9 cells was not reduced by the presence of heparin or the identified heparin-binding peptide, even though the peptide could bind to Sf9 cell surface and be efficiently internalized. Thus, our data suggest that, depending on the availability of the target molecules on the cell surface, baculoviruses can use two different methods, electrostatic interaction with heparan sulfate and more specific receptor binding, for cell attachment.