Xiaojing Yun

Ribosomal RACK1 promotes chemoresistance and growth in human hepatocellular carcinoma

Coordinated translation initiation is coupled with cell cycle progression and cell growth, whereas excessive ribosome biogenesis and translation initiation often lead to tumor transformation and survival. Hepatocellular carcinoma (HCC) is among the most common and aggressive cancers worldwide and generally displays inherently high resistance to chemotherapeutic drugs. We found that RACK1, the receptor for activated C-kinase 1, was highly expressed in normal liver and frequently upregulated in HCC. Aberrant expression of RACK1 contributed to in vitro chemoresistance as well as in vivo tumor growth of HCC. These effects depended on ribosome localization of RACK1. Ribosomal RACK1 coupled with PKCβII to promote the phosphorylation of eukaryotic initiation factor 4E (eIF4E), which led to preferential translation of the potent factors involved in growth and survival. Inhibition of PKCβII or depletion of eIF4E abolished RACK1-mediated chemotherapy resistance of HCC in vitro. Our results imply that RACK1 may function as an internal factor involved in the growth and survival of HCC and suggest that targeting RACK1 may be an efficacious strategy for HCC treatment.

Knockdown of BCL2L12 leads to cisplatin resistance in MDA-MB-231 breast cancer cells.

BCL2L12, a newly identified member of Bcl-2 family, contains a BH2 domain and a putative BH3 domain. It was found to be highly expressed in normal breast tissues, and was associated with favorable prognosis in breast cancer patients. Here, we reported that the mRNA levels of BCL2L12 and its transcript variant BCL2L12A could be upregulated upon cisplatin treatment in MDA-MB-231 breast cancer cells. Knockdown of BCL2L12 and BCL2L12A dramatically inhibited cisplatin-induced apoptosis. In contrast, ectopic expressions of each of the proteins promoted cisplatin-induced apoptosis. These results indicated that decreased expressions or loss of BCL2L12 and BCL2L12A may contribute to the cisplatin resistance in breast cancer patients. Furthermore, we found that cisplatin-induced downregulation of beta-catenin was partially suppressed in BCL2L12- and BCL2L12A-knocked down MDA-MB-231 cells, which indicated that knockdown of these two proteins may stabilize beta-catenin in cisplatin-induced apoptosis. In short, we proposed that BCL2L12 and BCL2L12A may play an important role in cisplatin-induced apoptosis in MDA-MB-231 breast cancer cells.

Molecular characterization of two novel isoforms and a soluble form of mouse CLEC-2.

CLEC-2 was first identified by sequence similarity to C-type lectin-like molecules with immune functions. Recently, human CLEC-2 has been reported as a receptor for the platelet-aggregating snake venom toxin rhodocytin and the endogenous sialoglycoprotein podoplanin. It has also been reported to facilitate the capture of HIV-1. However, investigation of mouse CLEC-2 (mCLEC-2) has little progressed after its identification. In this study, we identified two novel splicing variants of mCLEC-2 derived from omission of exon 2 and 2/4, respectively. These two variants had different expression profiles and subcellular localization from full-length mCLEC-2. Moreover, we observed that full-length mCLEC-2 could be cleaved probably by proteases sensitive to aprotinin and PMSF into a soluble form that partially existed as a disulfide-linked homodimer. The results presented here represent a further advancement toward the understanding of mCLEC-2.

Identification of β-1,4-galactosyltransferase I as a target gene of HBx-induced cell cycle progression of hepatoma cell ☆

BACKGROUND/AIMS The hepatitis B virus-encoded HBx protein contributes to hepatocarcinogenesis with largely unknown mechanisms. It is widely known that N-linked oligosaccharides on glycoproteins are structurally altered during malignant transformation and these alterations are often associated with malignant transformation of cells. beta-1,4-galactosyltransferase I (GalT I) contributes to the biosynthesis of Galbeta-->4GlcNAc structure in the outer chain moieties of N-glycans. METHODS The difference of GalT I expression between normal liver and hepatoma tissues were investigated; the effect of HBx on GalT I expression was investigated; the role of GalT I in hepatoma cell growth and HBx-induced hepatoma cell growth were investigated. RESULTS GalT I was highly expressed in hepatocellular carcinoma and transcriptionally up-regulated by HBx, and functioned as a positive growth regulator in hepatoma cells. Furthermore, decreasing the expression of GalT I in hepatoma cells reduced the ability of tumor formation in vivo and inhibited HBx-induced cell cycle progression. CONCLUSIONS HBx-induced GalT I expression might contribute to HBx-mediated HCC development and progression.

Down-regulation of β1,4GalT V at protein level contributes to arsenic trioxide-induced glioma cell apoptosis

Arsenic trioxide (As2O3) has considerable efficacy in treating solid tumors with induction of apoptosis with largely unknown mechanisms. Posttranslational processing of proteins by glycosylation could have multiple regulating roles in the process of apoptosis. Here, we found that the expression of beta1,6-linked GlcNAc-bearing N-glycans on cell surface protein was gradually decreased after induction of apoptosis by As2O3-treatment. And, As2O3 significantly decreased the protein expression level of beta1,4GalT V, which effectively galactosylates the beta1,6-GlcNAc branch of N-glycans and functions as a positive regulator in glioma development. Furthermore, interfering with the expression of beta1,4GalT V in human glioma cell markedly promoted As2O3-induced cell apoptosis and beta1,4GalT V overexpression significantly reduced As2O3-induced glioma cell apoptosis. Taken together, our results suggested that down-regulation of beta1,4GalT V expression plays an important role in As2O3-induced apoptosis, providing a new mechanism of As2O3-induced cell apoptosis and indicating that inhibitors of beta1,4GalT V may enhance the therapeutic efficiency of As2O3 for malignant glioma.

Laminarin-mediated targeting to Dectin-1 enhances antigen-specific immune responses

It has immense potential for immunotherapy and vaccination to target antigens to antigen-presenting cells (APCs). Here we described a method for delivering whole protein antigens to APCs via carbohydrate-mediated targeting of Dectin-1, which is a C-type lectin and mainly expresses on subpopulations of dendritic cells and macrophages. Laminarin, which is a beta-1-3 glucan and a typical ligand for Dectin-1, was chemically coupled to ovalbumin (OVA). Compared to OVA alone, the conjugate was effectively recognized and ingested by CHO cells stably expressing Dectin-1 and bound to bone marrow dendritic cells (BMDCs) via Dectin-1. Laminarin modification led to significant enhancement of OVA-specific CD4(+) T-cell response. Moreover, when used to immunize mice, the conjugate enhanced the primary IgG antibody response to OVA. Taken together, our data suggest that APCs targeting based on glucan-Dectin-1 interaction is a promising approach to improve vaccines.

Cyclin-dependent kinase 11p58 interacts with HBO1 and enhances its histone acetyltransferase activity

CDK11p58, a 58 kDa protein of the PITSLRE kinase family, plays an important role in cell cycle progression, and is closely related to cell apoptosis. To gain further insight into the function of CDK11p58, we screened a human fetal liver cDNA library for its interacting proteins using the yeast two‐hybrid system. Here we report that histone acetyltransferase (HAT) HBO1, a MYST family protein, interacts with CDK11p58 in vitro and in vivo. CDK11p58 and HBO1 colocalize in the cell nucleus. Recombinant CDK11p58 enhances the HAT activity of HBO1 significantly in vitro. Meanwhile, overexpression of CDK11p58 in mammalian cells leads to the enhanced HAT activity of HBO1 towards free histones. Thus, we conclude that CDK11p58 is a new interacting protein and a novel regulator of HBO1. Both of the proteins may be involved in the regulation of eukaryotic transcription.

RACK1 associates with CLEC-2 and promotes its ubiquitin-proteasome degradation

CLEC-2 is a C-type lectin-like receptor and plays an important role in platelet activation. Snake venom toxin rhodocytin and the endogenous sialoglycoprotein podoplanin are identified as ligands for CLEC-2 and function as stimulators in platelet activation. We also previously indentified two splice variants of murine CLEC-2 as well as a soluble fragment cleaved from the full-length form. However, little is known about the interacting partners with the cytoplasmic region of CLEC-2. In this study, we reported that RACK1, the receptor for activated C-kinase 1, associated with the cytoplasmic tail of CLEC-2. Moreover, overexpression of RACK1 decreased the stability of CLEC-2 through promoting its ubiquitin-proteasome degradation, without impairing surface expression and downstream signaling of CLEC-2. Taken together, these results suggest RACK1 as a novel modulator of CLEC-2 expression.

CDK11p58 represses vitamin D receptor-mediated transcriptional activation through promoting its ubiquitin–proteasome degradation

Vitamin D receptor (VDR) is a member of the nuclear receptor superfamily and regulates transcription of target genes. In this study, we identified CDK11(p58) as a novel protein involved in the regulation of VDR. CDK11(p58), a member of the large family of p34cdc2-related kinases, is associated with cell cycle progression, tumorigenesis, and apoptotic signaling. Our study demonstrated that CDK11(p58) interacted with VDR and repressed VDR-dependent transcriptional activation. Furthermore, overexpression of CDK11(p58) decreased the stability of VDR through promoting its ubiquitin-proteasome-mediated degradation. Taken together, these results suggest that CDK11(p58) is involved in the negative regulation of VDR.

Estrogen receptor α (ERα) mediates 17β-estradiol (E2)-activated expression of HBO1

BackgroundHBO1 (histone acetyltransferase binding to ORC1) is a histone acetyltransferase (HAT) which could exert oncogenic function in breast cancer. However, the biological role and underlying mechanism of HBO1 in breast cancer remains largely unknown. In the current study, we aimed to investigate the role of HBO1 in breast cancer and uncover the underlying molecular mechanism.MethodsImmunohistochemistry was applied to detect HBO1 protein expression in breast cancer specimens (n = 112). The expression of protein level was scored by integral optical density (IOD) for further statistical analyses using SPSS. Real-time PCR was used to simultaneously measure mRNA levels of HBO1. The HBO1 protein expression in breast cancer cells was confirmed by western blot.ResultsHBO1 was highly expressed in breast cancer tissues and significantly correlated with estrogen receptor α (ERα) (p < 0.001) and progestational hormone (PR) (p = 0.002). HBO1 protein level also correlated positively with histology grade in ERα positive tumors (p = 0.016) rather than ERα negative tumors. 17β-estradiol (E2) could upregulate HBO1 gene expression which was significantly inhibited by ICI 182,780 or ERα RNAi. E2-increased HBO1 protein expression was significantly suppressed by treatment with inhibitor of MEK1/2 (U0126) in T47 D and MCF-7 cells.ConclusionsHBO1 was an important downstream molecule of ERα, and ERK1/2 signaling pathway may involved in the expression of HBO1 increased by E2.