Seon Hwan Kim

PHF20 regulates NF-κB signalling by disrupting recruitment of PP2A to p65

Constitutive NF-κB activation in cancer cells is caused by defects in the signalling network responsible for terminating the NF-κB response. Here we report that plant homeodomain finger protein 20 (PHF20) maintains NF-κB in an active state in the nucleus by inhibiting the interaction between PP2A and p65. We show that PHF20 induces canonical NF-κB signalling by increasing the DNA-binding activity of NF-κB subunit p65. In PHF20 overexpressing cells, the termination of tumour necrosis factor-induced p65 phosphorylation is impaired whereas upstream signalling events triggered by tumour necrosis factor are unaffected. This effect strictly depends on the interaction between PHF20 and methylated lysine residues of p65, which hinders recruitment of PP2A to p65, thereby maintaining p65 in a phosphorylated state. We further show that PHF20 levels correlate with p65 phosphorylation levels in human glioma specimens. Our work identifies PHF20 as a novel regulator of NF-κB activation and suggests that elevated expression of PHF20 may drive constitutive NF-κB activation in some cancers.

New players in high fat diet-induced obesity: LETM1 and CTMP

OBJECTIVE Obesity contributes to insulin resistance and is a risk factor for diabetes. C-terminal modulator protein (CTMP) and leucine zipper/EF-hand-containing transmembrane protein 1 (LETM1) have been reported to influence the phosphoinositide 3-kinase (PI3K)/protein kinase B (PKB) signaling pathway via the modulation of PKB activity, a key player for insulin signaling. However, it remains unclear whether CTMP and LETM1 are associated with PI3K/PKB signaling in mouse models of obesity. MATERIALS/METHODS To address this question, we used two different mouse models of obesity, including high-fat diet (HFD)-induced diabetic mice and genetically modified obese mice (ob/ob mice). The levels of insulin-signaling molecules in these mice were determined by immunohistochemical and Western blot analyses. The involvement of CTMP and LETM1 in PI3K/PKB signaling was investigated in HEK293 cells by transient transfection and adenovirus-mediated infection. RESULTS We found that the levels of insulin receptor, phosphorylated PKB, and LETM1 were lower and the level of CTMP was higher in the adipose tissue of obese mice on an HFD compared to lean mice on a chow diet. Similar results were obtained in ob/ob mice. In HEK293 cells, the activation of PKB increased the LETM1 level, and inhibition of PKB increased the CTMP level. The overexpression of CTMP suppressed the insulin-induced increase in PKB phosphorylation, which was abrogated by co-overexpression with LETM1. CONCLUSION These results suggest that CTMP and LETM1 may participate in impaired insulin signaling in the adipose tissue of obese mice, raising the possibility that these parameters may serve as new candidate biomarkers or targets in the development of new therapeutic approaches for diabetes.

Involvement of S6K1 in mitochondria function and structure in HeLa cells

The major biological function of mitochondria is to generate cellular energy through oxidative phosphorylation. Apart from cellular respiration, mitochondria also play a key role in signaling processes, including aging and cancer metabolism. It has been shown that S6K1-knockout mice are resistant to obesity due to enhanced beta-oxidation, with an increased number of large mitochondria. Therefore, in this report, the possible involvement of S6K1 in regulating mitochondria dynamics and function has been investigated in stable lenti-shS6K1-HeLa cells. Interestingly, S6K1-stably depleted HeLa cells showed phenotypical changes in mitochondria morphology. This observation was further confirmed by detailed image analysis of mitochondria shape. Corresponding molecular changes were also observed in these cells, such as the induction of mitochondrial fission proteins (Drp1 and Fis1). Oxygen consumption is elevated in S6K1-depeleted HeLa cells and FL5.12 cells. In addition, S6K1 depletion leads to enhancement of ATP production in cytoplasm and mitochondria. However, the relative ratio of mitochondrial ATP to cytoplasmic ATP is actually decreased in lenti-shS6K1-HeLa cells compared to control cells. Lastly, induction of mitophagy was found in lenti-shS6K1-HeLa cells with corresponding changes of mitochondria shape on electron microscope analysis. Taken together, our results indicate that S6K1 is involved in the regulation of mitochondria morphology and function in HeLa cells. This study will provide novel insights into S6K1 function in mitochondria-mediated cellular signaling.

Recognition of transmembrane protein 39A as a Tumor-Specific marker in brain tumor

Transmembrane protein 39A (TMEM39A) belongs to the TMEM39 family. TMEM39A gene is a susceptibility locus for multiple sclerosis. In addition, TMEM39A seems to be implicated in systemic lupus erythematosus. However, any possible involvement of TMEM39A in cancer remains largely unknown. In the present report, we provide evidence that TMEM39A may play a role in brain tumors. Western blotting using an anti-TMEM39A antibody indicated that TMEM39A was overexpressed in glioblastoma cell lines, including U87-MG and U251-MG. Deep-sequencing transcriptomic profiling of U87-MG and U251-MG cells revealed that TMEM39A transcripts were upregulated in such cells compared with those of the cerebral cortex. Confocal microscopic analysis of U251-MG cells stained with anti-TMEM39A antibody showed that TMEM39A was located in dot-like structures lying close to the nucleus. TMEM39A probably located to mitochondria or to endosomes. Immunohistochemical analysis of glioma tissue specimens indicated that TMEM39A was markedly upregulated in such samples. Bioinformatic analysis of the Rembrandt knowledge base also supported upregulation of TMEM39A mRNA levels in glioma patients. Together, the results afford strong evidence that TMEM39A is upregulated in glioma cell lines and glioma tissue specimens. Therefore, TMEM39A may serve as a novel diagnostic marker of, and a therapeutic target for, gliomas and other cancers.

Mitochondrial transcription factor A (TFAM) is upregulated in glioma

Mitochondrial transcription factor A (TFAM), which was initially discovered as a transcription factor for mitochondrial DNA, has known to be critical for the regulation of mitochondrial DNA. However the possible involvement of TFAM in cancer is largely unknown. In this study, we have provided some evidence that TFAM may have a potential role in brain tumor. Western blot analysis with anti‑TFAM antibody indicated that TFAM is overexpressed in glioblastoma cell lines including U87MG and U251MG. Transcriptome profiling of U87MG and U251MG cells by using deep‑sequencing revealed that TFAM transcripts were upregulated in these cells compared to its of cerebral cortex. Confocal microscopic analysis of U251MG cells with anti‑TFAM antibody showed that TFAM is located to the dot‑like structure close to nucleus, probably mitochondria and endosome. Immunohistochemical analysis of glioma tissue specimens indicated that TFAM is highly upregulated. Bioinformatical analysis with Rembrandt knowledgebase also supported that TFAM mRNA is upregulated in glioma patients. Taken together, the results presented in this study obviously provided the evidence that TFAM was upregulated in glioma cell line and glioma tissue specimens. Therefore TFAM may be a novel diagnostic marker and therapeutic target for glioma and other cancer.

The roles of TRIO and F-actin-binding protein in glioblastoma cells

TRIO and F-actin-binding protein (TrioBP), which was initially discovered as a binding partner of Trio and F-actin, is a critical factor associated with hearing loss in humans. However, the function of TrioBP in cancer has not been investigated. In the present study, TrioBP expression was indicated to be highly elevated in U87-MG and U343-MG cells. Furthermore, the TrioBP mRNA expression level was markedly increased in U87-MG and U251-MG cells compared with that in cerebral cortex cells, as determined by deep sequencing. Comprehensive analysis of a public TCGA dataset confirmed that TrioBP expression is elevated in patients with glioblastoma. In summary, the present data indicate that TrioBP expression is increased in glioblastoma cell lines and in patients with glioma, suggesting that TrioBP has potential as a diagnostic marker or therapeutic agent for glioma.

Expression of PGC1α in glioblastoma multiforme patients

Peroxisome proliferator-activated receptor γ coactivator 1α (PGC1α) is a key modulator of mitochondrial biogenesis. It is a coactivator of multiple transcription factors and regulates metabolic processes. However, little is known about the expression and function of PGC1α in glioblastoma multiforme (GBM), the most prevalent and invasive type of brain tumor. The purpose of the present study was to investigate the biological function, localization and expression of PGC1α in GBM. It was observed that PGC1α expression is increased in the tumor cells, and a higher level of expression was observed in the mitochondria. Bioinformatics analyses identified that metabolic and mitochondrial genes were highly expressed in GBM cells, with a high PGC1α mRNA expression. Notably, mitochondrial function-associated genes were highly expressed in cells alongside high PGC1α expression. Collectively, the results of the present study indicate that PGC1α is associated with mitochondrial dysfunction in GBM and may have a role in tumor pathogenesis and progression.