Photoactivable Elimination of Tumorigenic Human Induced Pluripotent Stem Cells by Using a Lectin-Doxorubicin Prodrug Conjugate.

Human pluripotent stem cells (hPSCs) are attractive resources for regenerative medicine, but medical applications are hindered by their tumorigenic potential. Previously, a hPSC-specific lectin probe, rBC2LCN, was identified through comprehensive glycome analysis by using high-density lectin microarrays. Herein, a lectin-doxorubicin (DOX) prodrug conjugate, with controllable photolysis activation for the elimination of tumorigenic human induced pluripotent stem cells, has been developed. rBC2LCN was fused with a biotin-binding protein, tamavidin (BC2Tama), and the fusion protein was expressed in Escherichia coli and purified by means of affinity chromatography. BC2Tama was then conjugated with doxorubicin-photocleavable biotin (DOXPCB). The BC2Tama-DOXPCB conjugates were observed to bind to hPSCs followed by internalization. Upon exposure to ultraviolet light, DOX was released inside the cells, which allowed specific killing of the hPSCs. Thus, BC2Tama-DOXPCB should be useful for the targeted elimination of hPSCs contained in hPSC-derived cell therapy products. This is the first report of the generation of lectin-prodrug conjugates. BC2Tama should be applicable for the targeted delivery of various types of biotinylated compounds into hPSCs.

Plzf drives MLL-fusion-mediated leukemogenesis specifically in long-term hematopoietic stem cells.

Oncogenic transformation requires unlimited self-renewal. Currently, it remains unclear whether a normal capacity for self-renewal is required for acquiring an aberrant self-renewal capacity. Our results in a new conditional transgenic mouse showed that a mixed lineage leukemia (MLL) fusion oncogene, MLL-ENL, at an endogenous-like expression level led to leukemic transformation selectively in a restricted subpopulation of hematopoietic stem cells (HSCs) through upregulation of promyelocytic leukemia zinc finger (Plzf). Interestingly, forced expression of Plzf itself immortalized HSCs and myeloid progenitors in vitro without upregulation of Hoxa9/Meis1, which are well-known targets of MLL fusion proteins, whereas its mutant lacking the BTB/POZ domain did not. In contrast, depletion of Plzf suppressed the MLL-fusion-induced leukemic transformation of HSCs in vitro and in vivo. Gene expression analyses of human clinical samples showed that a subtype of PLZF-high MLL-rearranged myeloid leukemia cells was closely associated with the gene expression signature of HSCs. These findings suggested that MLL fusion protein enhances the self-renewal potential of normal HSCs to develop leukemia, in part through a Plzf-driven self-renewal program.

Glycan profiling of the gut microbiota by Glycan-seq.

Bacterial glycans modulate the cross talk between the gut microbiota and its host. However, little is known about these glycans because of the lack of appropriate technology to study them. In this study, we applied Glycan-seq technology for glycan profiling of the intact gut microbiota of mice. The evaluation of cultured gram-positive (Deinococcus radiodurans) and gram-negative (Escherichia coli) bacteria showed significantly distinct glycan profiles between these bacteria, which were selected and further analyzed by flow cytometry. The results of flow cytometry agreed well with those obtained by Glycan-seq, indicating that Glycan-seq can be used for bacterial glycan profiling. We thus applied Glycan-seq for comparative glycan profiling of pups and adult mice gut microbiotas. The glycans of the pups and adult microbiotas had significantly distinct glycan profiles, which reflect the different bacterial compositions of pups and adult gut microbiotas based on 16S rRNA gene sequencing.α2-6Sia-binders bound specifically to the pups microbiota. Lectin pull-down followed by 16S rRNA gene sequencing of the pups microbiota identified Lactobacillaceae as the most abundant bacterial family with glycans reacting with α2-6Sia-binders. The Glycan-seq system can reveal the glycan profile of the intact bacterial gut microbiota.

Integrated analysis of glycan and RNA in single cells.

Single-cell sequencing has emerged as an indispensable technology to dissect cellular heterogeneity but never been applied to the simultaneous analysis of glycan and RNA. Using oligonucleotide-labeled lectins, we first established lectin-based glycan profiling of single cells by sequencing (scGlycan-seq). We then combined the scGlycan-seq with single-cell transcriptome profiling for joint analysis of glycan and RNA in single cells (scGR-seq). Using scGR-seq, we analyzed the two modalities in human induced pluripotent stem cells (hiPSCs) before and after differentiation into neural progenitor cells at the single-cell resolution. The combination of RNA and glycan separated the two cell types clearer than either one of them. Furthermore, integrative analysis of glycan and RNA modalities in single cells found known and unknown lectins that were specific to hiPSCs and coordinated with neural differentiation. Taken together, we demonstrate that scGR-seq can reveal the cellular heterogeneity and biological roles of glycans across multicellular systems.

Oriented immobilization of rBC2LCN lectin for highly sensitive detection of human pluripotent stem cells using cell culture supernatants.

Human pluripotent stem cells (hPSCs) are considered ideal cell sources for regenerative medicine, but their clinical and industrial applications are hindered by their tumorigenic potential. We previously identified an hPSC-specific lectin, rBC2LCN, that recognizes the podocalyxin glycoprotein secreted by undifferentiated hPSCs into the culture media. Using biotinylated rBC2LCN and a peroxidase-labeled R-10G antibody, we developed a sandwich assay for the detection of tumorigenic hPSCs. In this assay, the lectin is randomly immobilized on streptavidin-coated microplates to capture hPSC-derived podocalyxin. In the present study, rBC2LCN was genetically fused with polystyrene-binding peptides (PS-tags) for direct, site-specific, and oriented immobilization on polystyrene microplates. rBC2LCN lectins fused with PS-tags at the C-terminus were successfully overexpressed as a soluble form in Escherichia coli and then purified by affinity chromatography. We optimized the various parameters (protein and NaCl concentration, buffer pH, and blocking agents) of the sandwich assay by using PS-tagged rBC2LCN and the R-10G antibody. Finally, the lower limit of detection (LLOD) of the sandwich assay for hPSCs was examined. The LLOD was 2.2-fold lower than that achieved with the previous method. Considering that the developed method does not require the precoating of polystyrene microplates with streptavidin, it provides a cost-effective approach for the highly sensitive detection of hPSCs residing in hPSC-derived cell therapeutics.

Elimination of tumorigenic human pluripotent stem cells by a recombinant lectin-toxin fusion protein.

The application of stem-cell-based therapies in regenerative medicine is hindered by the tumorigenic potential of residual human pluripotent stem cells. Previously, we identified a human pluripotent stem-cell-specific lectin probe, called rBC2LCN, by comprehensive glycome analysis using high-density lectin microarrays. Here we developed a recombinant lectin-toxin fusion protein of rBC2LCN with a catalytic domain of Pseudomonas aeruginosa exotoxin A, termed rBC2LCN-PE23, which could be expressed as a soluble form from the cytoplasm of Escherichia coli and purified to homogeneity by one-step affinity chromatography. rBC2LCN-PE23 bound to human pluripotent stem cells, followed by its internalization, allowing intracellular delivery of a cargo of cytotoxic protein. The addition of rBC2LCN-PE23 to the culture medium was sufficient to completely eliminate human pluripotent stem cells. Thus, rBC2LCN-PE23 has the potential to contribute to the safety of stem-cell-based therapies.

Identification of RHOXF2 (PEPP2) as a cancer-promoting gene by expression cloning.

Multiple mutations contribute to establish cancers. We have searched for potential oncogenes by screening cDNA libraries derived from gastric cancer cell lines, pancreatic cancer cell lines and glioma cell lines, using retrovirus-mediated expression cloning. Two types of interleukin-3 (IL-3)-dependent cell lines, Ba/F3 and HF6, were transduced with the cDNA libraries and several genes that render these cells factor-independent were identified including PIM-1, PIM-2, PIM-3, GADD45B and reproductive homeobox genes on the X chromosome gene F2 (RHOXF2). Although no mutation in these genes was found, these molecules were highly expressed in cancer cell lines and they may play important roles in cell transformation. Among them, we focused on a transcriptional repressor RHOXF2. Transduction of RHOXF2 rendered HF6 cells factor-independent, while knockdown of RHOXF2 inhibited growth of the HGC27 gastric cancer cell line which highly expresses RHOXF2. In addition, RHOXF2-transduced HF6 cells quickly induced leukemia when transplanted into sublethally irradiated mice. Moreover, RHOXF2 is highly expressed in some leukemia cell lines and a variety of human cancer samples including colon and lung cancers. Thus, these results indicate that RHOXF2 is involved in carcinogenesis.