SEPT7 Interacts with KIF20A and Regulates the Proliferative State of Neural Progenitor Cells During Cortical Development.

Balanced proliferation and differentiation of neural progenitor cells (NPCs) are critical for brain development, but how the process is regulated and what components of the cell division machinery is involved are not well understood. Here we report that SEPT7, a cell division regulator originally identified in Saccharomyces cerevisiae, interacts with KIF20A in the intercellular bridge of dividing NPCs and plays an essential role in maintaining the proliferative state of NPCs during cortical development. Knockdown of SEPT7 in NPCs results in displacement of KIF20A from the midbody and early neuronal differentiation. NPC-specific inducible knockout of Sept7 causes early cell cycle exit, precocious neuronal differentiation, and ventriculomegaly in the cortex, but surprisingly does not lead to noticeable cytokinesis defect. Our data uncover an interaction of SEPT7 and KIF20A during NPC divisions and demonstrate a crucial role of SEPT7 in cell fate determination. In addition, this study presents a functional approach for identifying additional cell fate regulators of the mammalian brain.

Targeting CD26 suppresses proliferation of malignant mesothelioma cell via downmodulation of ubiquitin-specific protease 22.

Malignant pleural mesothelioma (MPM) is an aggressive malignancy arising from mesothelial lining of pleura. It is associated with a poor prognosis, partly due to the lack of a precise understanding of the molecular mechanisms associated with its malignant behavior. In the present study, we expanded on our previous studies on cell cycle control of MPM cells by targeting CD26 molecule with humanized anti-CD26 monoclonal antibody (HuCD26mAb), focusing particularly on ubiquitin-specific protease 22 (USP22). We showed that USP22 protein expression is detected in clinical specimens of MPM and that USP22 knockdown, as well as CD26 knockdown, significantly inhibits the growth and proliferation of MPM cells in vitro and in vivo. Moreover, depletion of both USP22 and CD26 suppresses MPM cell proliferation even more profoundly. Furthermore, expression levels of USP22 correlate with those of CD26. HuCD26mAb treatment induces a decrease in USP22 level through its interaction with the CD26 molecule, leading to increased levels of ubiquitinated histone H2A and p21. By demonstrating a CD26-related linkage with USP22 in MPM cell inhibition induced by HuCD26mAb, our present study hence characterizes USP22 as a novel target molecule while concurrently suggesting a new therapeutic strategy for MPM.

Glucose metabolism induces mono-ubiquitination of histone H2B in mammalian cells.

Histone modifications play an important role in transcriptional regulation and are intimately involved in important biological and disease processes. Despite their functional significance, whether and how extracellular signals modulate histone modifications are not well defined. Using mono-ubiquitination of histone H2B as a model system, we have previously shown that mono-ubiquitination of histone H2B is induced by glucose through glycolysis in budding yeast Saccharomyces cerevisiae. Because histones are well conserved proteins among eukaryotes and glycolysis is the most conserved metabolic pathway, we reasoned that the glucose-glycolysis-uH2B signal pathway originally discovered in yeast may be conserved in human cells. Using cultured human glioma cells as a model, we show in this report that extracellular media modulated global levels of mono-ubiquitination of histone H2B at K120 (uH2B). Nutrient deprivation removed the ubiquitin moiety of uH2B. Glucose-containing media induced uH2B in the cells while media lacking glucose had no effect on the induction of uH2B, suggesting that glucose was required for inducing uH2B in the cells. In contrast, non-metabolic glucose analogs were defective in inducing uH2B, suggesting that glucose metabolism was required for glucose-induced mono-ubiquitination in the cultured glioma cells. Moreover, shRNA knockdown of PKM2, an essential enzyme for glycolysis in malignant tumors, inhibited mono-ubiquitination of histone H2B in these cells. Taken together, our previous and current results demonstrate that the novel glucose-glycolysis-uH2B signal pathway is well conserved from yeast to mammalian cells, providing an evolutionarily-conserved regulatory mechanism of histone modifications.

Resveratrol induces cellular senescence with attenuated mono-ubiquitination of histone H2B in glioma cells.

Resveratrol (3,4',5-trihydroxy-trans-stilbene), a polyphenol naturally occurring in grapes and other plants, has cancer chemo-preventive effects and therapeutic potential. Although resveratrol modulates multiple pathways in tumor cells, how resveratrol or its affected pathways converge on chromatin to mediate its effects is not known. Using glioma cells as a model, we showed here that resveratrol inhibited cell proliferation and induced cellular hypertrophy by transforming spindle-shaped cells to enlarged, irregular and flatten-shaped ones. We further showed that resveratrol-induced hypertrophic cells expressed senescence-associated-ß-galactosidase, suggesting that resveratrol-induced cellular senescence in glioma cells. Consistent with these observations, we demonstrated that resveratrol inhibited clonogenic efficiencies in vitro and tumor growth in a xenograft model. Furthermore, we found that acute treatment of resveratrol inhibited mono-ubiquitination of histone H2B at K120 (uH2B) in breast, prostate, pancreatic, lung, brain tumor cells as well as primary human cells. Chronic treatment with low doses of resveratrol also inhibited uH2B in the resveratrol-induced senescent glioma cells. Moreover, we showed that depletion of RNF20, a ubiquitin ligase of histone H2B, inhibited uH2B and induced cellular senescence in glioma cells in vitro, thereby recapitulated the effects of resveratrol. Taken together, our results suggest that uH2B is a novel direct or indirect chromatin target of resveratrol and RNF20 plays an important role in inhibiting cellular senescence programs that are intact in glioma cells.

Regulation of cancer stem cell properties by CD9 in human B-acute lymphoblastic leukemia.

Although the prognosis of acute lymphoblastic leukemia (ALL) has improved considerably in recent years, some of the cases still exhibit therapy-resistant. We have previously reported that CD9 was expressed heterogeneously in B-ALL cell lines and CD9(+) cells exhibited an asymmetric cell division with greater tumorigenic potential than CD9(-) cells. CD9(+) cells were also serially transplantable in immunodeficient mice, indicating that CD9(+) cell possess self-renewal capacity. In the current study, we performed more detailed analysis of CD9 function for the cancer stem cell (CSC) properties. In patient sample, CD9 was expressed in the most cases of B-ALL cells with significant correlation of CD34-expression. Gene expression analysis revealed that leukemogenic fusion proteins and Src family proteins were significantly regulated in the CD9(+) population. Moreover, CD9(+) cells exhibited drug-resistance, but proliferation of bulk cells was inhibited by anti-CD9 monoclonal antibody. Knockdown of CD9 remarkably reduced the leukemogenic potential. Furthermore, gene ablation of CD9 affected the expression and tyrosine-phosphorylation of Src family proteins and reduced the expression of histone-deubiquitinase USP22. Taken together, our results suggest that CD9 links to several signaling pathways and epigenetic modification for regulating the CSC properties of B-ALL.

Identification of cancer stem cell markers in human malignant mesothelioma cells.

Malignant mesothelioma (MM) is an aggressive and therapy-resistant neoplasm arising from the pleural mesothelial cells and usually associated with long-term asbestos exposure. Recent studies suggest that tumors contain cancer stem cells (CSCs) and their stem cell characteristics are thought to confer therapy-resistance. However, whether MM cell has any stem cell characteristics is not known. To understand the molecular basis of MM, we first performed serial transplantation of surgical samples into NOD/SCID mice and established new cell lines. Next, we performed marker analysis of the MM cell lines and found that many of them contain SP cells and expressed several putative CSC markers such as CD9, CD24, and CD26. Interestingly, expression of CD26 closely correlated with that of CD24 in some cases. Sorting and culture assay revealed that SP and CD24(+) cells proliferated by asymmetric cell division-like manner. In addition, CD9(+) and CD24(+) cells have higher potential to generate spheroid colony than negative cells in the stem cell medium. Moreover, these marker-positive cells have clear tendency to generate larger tumors in mouse transplantation assay. Taken together, our data suggest that SP, CD9, CD24, and CD26 are CSC markers of MM and could be used as novel therapeutic targets.

Inactivation of Ras function by allele-specific peptide aptamers.

One challenge facing biology is the elucidation of the function of the estimated 30 000 human genes and their polymorphic variants. Reagents that affect the activity of specific genes will be useful in the dissection of cellular regulatory networks. Here, as a test case, we used a two-bait two-hybrid system to identify peptide aptamers that distinguish allelic forms of H-Ras. Some of these anti-Ras aptamters inhibit the interaction of oncogenic Ras with c-Raf1 in vitro, and abolish EGF-stimulated activation of c-Raf1 in vivo. These experiments show that the inactivation of protein function by peptide aptamers represents a viable approach to the understanding and control of signaling pathways and oncogenic missense alleles.

Coupling of glucose deprivation with impaired histone H2B monoubiquitination in tumors.

Metabolic reprogramming is associated with tumorigenesis. However, glucose metabolism in tumors is poorly understood. Here, we report that glucose levels are significantly lower in bulk tumor specimens than those in normal tissues of the same tissue origins. We show that mono-ubiquitinated histone H2B (uH2B) is a semi-quantitative histone marker for glucose. We further show that loss of uH2B occurs specifically in cancer cells from a wide array of tumor specimens of breast, colon, lung and additional 23 anatomic sites. In contrast, uH2B levels remain high in stromal tissues or non-cancerous cells in the tumor specimens. Taken together, our data suggest that glucose deficiency and loss of uH2B are novel properties of cancer cells in vivo, which may represent important regulatory mechanisms of tumorigenesis.

High-density cell microarrays for parallel functional determinations.

Whole-genome sequencing projects have generated a wealth of gene sequences from a variety of organisms. A major challenge is to rapidly uncover gene regulatory circuits and their functional manifestations at the cellular level. Here we report the coupled fabrication of nanocraters ranging in size from 100 pL to 1.5 nL on permeable membranes for culturing cells. Using this approach, we developed bacterial and yeast cell microarrays that allowed phenotypic determinations of gene activities and drug targets on a large scale. Cell microarrays will therefore be a particularly useful tool for studying phenotypes of gene activities on a genome-wide scale.

Carbohydrates induce mono-ubiquitination of H2B in yeast.

Histone modifications have emerged to be a major regulatory mechanism for gene expression (1-4). However, it is not clear how histone modifications are physiologically regulated. Here, we show that mono-ubiquitinated H2B at lysine 123 (uH2B) in the yeast (Saccharomyces cerevisiae) is present in exponential phase and absent in stationary phase. A wide array of carbohydrates or sugars, including glucose, fructose, mannose, and sucrose, are capable of inducing uH2B in stationary phase yeast. In contrast, non-metabolic glucose analogs are defective in inducing uH2B. Furthermore, uH2B induction is inhibited by iodoacetate, an inhibitor of glyceraldehyde-3-phosphate dehydrogenase in glycolysis. Moreover, uH2B induction is markedly impaired in yeast mutants, in which glycolytic genes are deleted. These data indicate that glycolysis is required for the carbohydrate-induced mono-ubiquitination of H2B at lysine 123. Therefore, our study reveals a novel paradigm of metabolic regulation of histone modifications.

Activation of p53 by protein inhibitor of activated Stat1 (PIAS1).

The tumor suppressor protein p53 functions as a transcriptional factor that activates genes controlling cell cycle arrest and apoptosis. Here, we report that protein inhibitor of activated Stat1 (PIAS1) interacts with the tetramerization and C-terminal regulatory domains of p53 in yeast two-hybrid analyses. Endogenous PIAS1 is also associated with endogenous p53 in mammalian cells. Ectopic expression of PIAS1 activates p53-mediated expression in mouse embryonic fibroblast cells (p53(-/-)) as well as a variety of other cell lines. Furthermore, ectopic expression of PIAS1 induces p53-mediated expression of cyclin-dependent kinase inhibitor p21 and G(1) arrest of the cell cycle in H1299 cells. In addition, a PIAS1 mutant without the RING-finger domain required for sumoylation could still activate p53-mediated gene expression, indicating that activation of p53 by PIAS1 does not require the RING-finger domain. Taken together, our results suggest that PIAS1 is a novel activator of p53.