NOVA1 prevents overactivation of the unfolded protein response and facilitates chromatin access during human white adipogenesis.

The molecular mechanism underlying white adipogenesis in humans has not been fully elucidated beyond the transcriptional level. Here, we found that the RNA-binding protein NOVA1 is required for the adipogenic differentiation of human mesenchymal stem cells. By thoroughly exploring the interactions between NOVA1 and its binding RNA, we proved that NOVA1 deficiency resulted in the aberrant splicing of DNAJC10 with an in-frame premature stop codon, reduced DNAJC10 expression at the protein level and hyperactivation of the unfolded protein response (UPR). Moreover, NOVA1 knockdown abrogated the down-regulation of NCOR2 during adipogenesis and up-regulated the 47b+ splicing isoform, which led to decreased chromatin accessibility at the loci of lipid metabolism genes. Interestingly, these effects on human adipogenesis could not be recapitulated in mice. Further analysis of multispecies genomes and transcriptomes indicated that NOVA1-targeted RNA splicing is evolutionarily regulated. Our findings provide evidence for human-specific roles of NOVA1 in coordinating splicing and cell organelle functions during white adipogenesis.

De-dimerization of PTB is catalyzed by PDI and is involved in the regulation of p53 translation.

Polypyrimidine tract-binding protein (PTB) is an RNA binding protein existing both as dimer and monomer and shuttling between nucleus and cytoplasm. However, the regulation of PTB dimerization and the relationship between their functions and subcellular localization are unknown. Here we find that PTB presents as dimer and monomer in nucleus and cytoplasm respectively, and a disulfide bond involving Cysteine 23 is critical for the dimerization of PTB. Additionally, protein disulfide isomerase (PDI) is identified to be the enzyme that catalyzes the de-dimerization of PTB, which is dependent on the CGHC active site of the a' domain of PDI. Furthermore, upon DNA damage induced by topoisomerase inhibitors, PTB is demonstrated to be de-dimerized with cytoplasmic accumulation. Finally, cytoplasmic PTB is found to associate with the ribosome and enhances the translation of p53. Collectively, these findings uncover a previously unrecognized mechanism of PTB dimerization, and shed light on the de-dimerization of PTB functionally linking to cytoplasmic localization and translational regulation.

Human Papillomavirus 16 oncoprotein E7 retards mitotic progression by blocking Mps1-MAP4 signaling cascade.

Human epithelial cells can be infected by more than 200 types of human papilloma viruses (HPVs), and persistent HPV infections lead to cervical cancer or other deadly cancers. It has been established that mitotic progression is critical for HPV16 infection, but the underlying mechanism remains unknown. Here, we report that oncoprotein E7 of HPV16 but not HPV18 retards mitotic progression in host cell by direct binding to the C terminus of Microtubule-Associated Protein 4 (MAP4). MAP4 is a novel bona fide target of HPV16E7 protein which binds and recruits the latter to spindle microtubule in mitosis. HPV16E7 protein promotes MAP4 stability by inhibiting MAP4 phosphorylation- mediated degradation to increase the stability of microtubule polymerization and cause an extend mitotic progression. We further uncovered that Mps1 is a kinase of MAP4, and E7-MAP4 binding blocks Mps1 phosphorylation of MAP4, thereby interrupting phosphorylation-dependent MAP4 degradation. Mutations of MAP4 at T927ES928E partially abolished E7-binding capacity and rescued mitotic progression in host cells. In conclusion, our study reveals a molecular mechanism by which HPV16E7 perturbs host mitotic progression by interfering Mps1-MAP4 signaling cascade, which results in an extended infection window and may facilitate the persistent HPV16 infection.

Suppression of PTBP1 signaling is responsible for mesenchymal stem cell induced invasion of low malignancy cancer cells.

Mesenchymal stem cells (MSCs) hold great promise as attractive vehicles to deliver therapeutic agents against cancer, while the cross-talk between MSCs and cancer cells remains controversial. Here in an indirect co-culture system we observed that MSCs induced the malignancy transformation of low malignancy cancer cells HT29 and MCF7, whereas MSCs were reprogrammed by high malignancy cancer cells HCT116 and MDA-MB-231 without exerting an obvious influence on them. We further demonstrated that the RNA-binding protein polypyrimidine tract-binding protein 1 (PTBP1) was suppressed in low malignancy cancer cells co-cultured with MSCs. Moreover, shRNA mediated silencing of PTBP1 could promote the invasiveness of HT29 cells while over-expression of PTBP1 attenuate the MSC-induced invasion of HT29 cells. Our results suggested that differential effects of MSCs on the invasion of cancer cells partially corresponded to PTBP1 expression in cancer cells and the maintenance of biological characteristics in MSCs, which insight could provide a theoretical basis for evaluating the safety of MSC application and PTBP1 targeting in cancer treatment.

Epigenetic silencing of TET2 and TET3 induces an EMT-like process in melanoma.

Epithelial-Mesenchymal Transition (EMT) is a critical step in the progression of cancer. Malignant melanoma, a cancer developed from pigmented melanocytes, metastasizes through an EMT-like process. Ten-eleven translocation (TET) enzymes, catalyzing the conversion of 5-methylcytosine (5mC) to 5-hydroxylmethylcytosine (5-hmC), are down regulated in melanoma. However, their roles in the progression and the EMT-like process of melanoma are not fully understood. Here we report that DNA methylation induced silencing of TET2 and TET3 are responsible for the EMT-like process and the metastasis of melanoma. TET2 and TET3 are down regulated in the TGF-ß1-induced EMT-like process, and the knocking down of TET2 or TET3 induced this EMT-like process. A DNA demethylating agent antagonized the TGF-ß-induced suppression of TET2 and TET3. Furthermore, a ChIP analysis indicated that enhanced recruitment of DNMT3A (DNA Methyltransferase 3A) is the mechanism by which TGF-ß induces the silencing of TET2 and TET3. Finally, the overexpression of the TET2 C-terminal sequence partially rescues the TGF-ß1-induced EMT-like process in vitro and inhibits tumor growth and metastasis in vivo. Hence, our data suggest an epigenetic circuitry that mediates the EMT activated by TGF-ß. As an effector, DNMT3A senses the TGF-ß signal and silences TET2 and TET3 promoters to induce the EMT-like process and metastasis in melanoma.

A Preliminary Study on RCN3 Protein Expression in Non-small Cell Lung Cancer.

BACKGROUND: Reticulocalbin 3 (RCN3), a member of CREC (Cab45/reticulocalbin/ ERC-45/calumenin) family protein, is located in the secretory pathway of endoplasmic reticulum (ER) of living cells. Disruption of RCN3 leads to failure of lung function in the mouse model. Although ER stress has been associated with the development of a variety of tumors, the role of RCN3 in development of non-small cell lung cancer (NSCLC) in human is unknown at present. METHODS: In this study a total of 41 paired NSCLC specimens (cancer group) and the adjacent normal tissues (control group) were obtained from patients undergoing lung lobectomy or pneumonectomy surgeries in Beijing Shijitan Hospital, Capital Medical University. The RCN3 mRNA and protein level in each clinical sample was determined using quantitative real time-PCR and immunoblotting, respectively. Immunohistochemistry analysis was utilized to compare the protein expressional patterns of RCN3 between the two clinical sample groups. RESULTS: Immunoblotting showed that levels of RCN3 protein in the NSCLC tissues were significantly lower than those in the control group (p < 0.001), suggesting ER stress is closely associated with the cancer cells. Accordingly, the ER stress protein GRP78 (glucose-regulated protein 78, also known as BIP) was remarkably upregulated in the cancer group (p < 0.05). Within the cancer group, a significant difference in RCN3 protein expression was observed in squamous cell carcinoma versus adenocarcinoma (p < 0.05). In the lung cancer group, however, RCN3 protein levels were not correlated with the age and the gender. In addition, RCN3 mRNA levels showed no significant difference between the cancer and the control groups, suggesting that the differential regulation of RCN3 is likely at post-transcription stage in NSCLC. CONCLUSIONS: Our study showed that RCN3 protein level was significantly down regulated in NSCLC, suggesting a potential correlation between RCN3 protein depletion and development of NSCLC. Although the exact cause-effect relationship between RCN3 and NSCLC needs to be further investigated, the study helps to shed additional lights on the molecular regulation of the lung cancer.

Effects of co-culturing BMSCs and auricular chondrocytes on the elastic modulus and hypertrophy of tissue engineered cartilage.

Co-culture of BMSCs and chondrocytes is considered as a promising strategy to generate tissue engineered cartilage as chondrocytes induce the chondrogenesis of BMSCs and inhibit the hypertrophy of engineered cartilage. Because the tissue specific stem/progenitor cells have been isolated from mature tissues including auricular cartilage, we hypothesized that adding stem cells to auricular chondrocytes in co-culture would also enhance the quality of engineered cartilage. In the present study, using the histological assay, biomechanical evaluation, and quantitative analysis of gene expression, we compared different strategies of auricular chondrocytes, BMSCs induction, and co-culture at different ratios on PGA/PLA scaffolds to construct tissue engineered elastic cartilage in vitro and in vivo. The up-regulation of RUNX2 and down-regulation of SOX9 were found in BMSCs chondrogenic induction group, which might imply a regulatory mechanism for the hypertrophy and potential osteogenic differentiation. Engineered cartilage in co-culture 5:5 group showed the densest elastic fibers and the highest Young's modulus, which were consistent with the expression profile of cartilage matrix-related genes including DCN and LOXL2 genes. Moreover, the better proliferative and chondrogenic potentials of engineered cartilage in co-culture 5:5 group were demonstrated by the stronger expression of Ki67 and Dlk1.