Han-chun Chen

Twist: a molecular target in cancer therapeutics

Twist, the basic helix-loop-helix transcription factor, is involved in the process of epithelial to mesenchymal transitions (EMTs), which play an essential role in cancer metastasis. Overexpression of Twist or its promoter methylation is a common scenario in metastatic carcinomas. Twist is activated by a variety of signal transduction pathways, including Akt, signal transducer and activator of transcription 3, mitogen-activated protein kinase, Ras, and Wnt signaling. Activated Twist upregulates N-cadherin and downregulates E-cadherin, which are the hallmarks of EMT. Moreover, Twist plays an important role in some physiological processes involved in metastasis, like angiogenesis, invadopodia, extravasation, and chromosomal instability. Twist also protects cancer cells from apoptotic cell death. In addition, Twist is responsible for the stemness of cancer cells and the generation of drug resistance. Recently, targeting Twist has gained significant interests in cancer therapeutics. The inactivation of Twist by small RNA technology or chemotherapeutic approach has been proved successful. Moreover, several inhibitors which are antagonistic to the upstream or downstream molecules of Twist signaling pathways have also been identified. Development of potential treatment strategies by targeting Twist has a great promise in cancer therapeutics.

Anticancer activities of Nigella sativa (black cumin).

Nigella sativa has been used as traditional medicine for centuries. The crude oil and thymoquinone (TQ) extracted from its seeds and oil are effective against many diseases like cancer, cardiovascular complications, diabetes, asthma, kidney disease etc. It is effective against cancer in blood system, lung, kidney, liver, prostate, breast, cervix, skin with much safety. The molecular mechanisms behind its anticancer role is still not clearly understood, however, some studies showed that TQ has antioxidant role and improves bodys defense system, induces apoptosis and controls Akt pathway. Although the anti-cancer activity of N. sativa components was recognized thousands of years ago but proper scientific research with this important traditional medicine is a history of last 2∼3 decades. There are not so many research works done with this important traditional medicine and very few reports exist in the scientific database. In this article, we have summarized the actions of TQ and crude oil of N. sativa against different cancers with their molecular mechanisms.

Regulatory effects of resveratrol on antioxidant enzymes: A mechanism of growth inhibition and apoptosis induction in cancer cells

Resveratrol (RSV) is a natural polyphenol that is known as a powerful chemopreventive and chemotherapeutic anticancer molecule. This study focused on the effects of RSV on the activities and expression levels of antioxidant enzymes in the cancer cells. Prostate cancer PC-3 cells, hepatic cancer HepG2 cells, breast cancer MCF-7 cells and the non-cancerous HEK293T kidney epithelial cells were treated with a wide range of RSV concentrations (10-100 μM) for 24–72 h. Cell growth was estimated by trypan blue staining, activities of the antioxidant enzymes were measured spectrophotometrically, expression levels of the antioxidant enzymes were quantified by digitalizing the protein band intensities on Western blots, and the percentage of apoptotic cells was determined by flow cytometry. Treatment with a low concentration of RSV (25 μM) significantly increased superoxide dismutase (SOD) activity in PC-3, HepG2 and MCF-7 cells, but not in HEK293T cells. Catalase (CAT) activity was increased in HepG2 cells, but no effect was found on glutathione peroxidase (GPX) upon RSV treatment. RSV-induced SOD2 expression was observed in cancer cells, although the expression of SOD1, CAT and GPX1 was unaffected. Apoptosis increased upon RSV treatment of cancer cells, especially in PC-3 and HepG2 cells. Together, our data demonstrated that RSV inhibits cancer cell growth with minimal effects on non-cancerous cells. We postulate that the disproportional up-regulation of SOD, CAT and GPX expression and enzymatic activity in cancer cells results in the mitochondrial accumulation of H2O2, which in turn induces cancer cell apoptosis.

Genetic polymorphisms of metabolic enzymes—CYP1A1, CYP2D6, GSTM1, and GSTT1, and gastric carcinoma susceptibility

Genetic polymorphisms in metabolic enzymes are associated with numerous cancers. In this study, the relationships between genetic polymorphisms of phase I metabolic enzymes including cytochrome P450 1A1 (CYP1A1), CYP2D6 and phase II metabolic enzymes such as glutathione S-transferase M1 (GSTM1) and GSTT1 and gastric carcinoma susceptibility were investigated. Genomic DNA was isolated from the peripheral blood of 129 healthy controls and 123 gastric carcinoma patients from Han ethnic group of Hunan Province located in Central South China. The genetic polymorphisms of the above mentioned enzymes were analyzed using PCR-RFLP techniques. There was no significant difference among the frequencies of CYP1A1 and/or CYP2D6 gene’s wild type, heterozygous or homozygous mutations between the gastric carcinoma group and control group. But the differences among the frequencies of GSTM1 and GSTT1 null genotype between the gastric carcinoma and control group were significant (both P < 0.05). Also there were significant differences in the frequencies of GSTM1 null in high/high–middle differentiated, middle differentiated, middle–low differentiated and low differentiated gastric tumor separately. GSTM1 null showed an increased risk in middle–low differentiated and low differentiated gastric carcinoma type, but GSTT1 null was not a risk factor for the four pathological types of gastric carcinoma mentioned above. We report here that the genotypes of CYP1A1 and CYP2D6 are not associated with gastric carcinoma risk; GSTM1 null, but not GSTT1 null inheritably increases risk of some pathological types of gastric carcinoma in Han ethnic population of Hunan Province.

Repressive effects of resveratrol on androgen receptor transcriptional activity

Background The chemopreventive effects of resveratrol (RSV) on prostate cancer have been well established; the androgen receptor (AR) plays pivotal roles in prostatic tumorigenesis. However, the exact underlying molecular mechanisms about the effects of RSV on AR have not been fully elucidated. A model system is needed to determine whether and how RSV represses AR transcriptional activity. Methodology The AR cDNA was first cloned into the retroviral vector pOZ-N and then integrated into the genome of AR-negative HeLa cells to generate the AR(+) cells. The constitutively expressed AR was characterized by monitoring hormone-stimulated nuclear translocation, DNA binding, and transcriptional activation, with the AR(-) cells serving as controls. AR(+) cells were treated with RSV, and both AR protein levels and AR transcriptional activity were measured simultaneously. Chromatin immunoprecipitation (ChIP) assays were used to detect the effects of RSV on the recruitment of AR to its cognate element (ARE). Results AR in the AR (+) stable cell line functions in a manner similar to that of endogenously expressed AR. Using this model system we clearly demonstrated that RSV represses AR transcriptional activity independently of any effects on AR protein levels. However, neither the hormone-mediated nucleus translocation nor the AR/ARE interaction was affected by RSV treatment. Conclusion We demonstrated unambiguously that RSV regulates AR target gene expression, at least in part, by repressing AR transcriptional activity. Repressive effects of RSV on AR activity result from mechanisms other than the affects of AR nuclear translocation or DNA binding.

Polymorphisms of DNA repair genes XPD , XRCC1 , and OGG1 , and lung adenocarcinoma susceptibility in Chinese population

Lung adenocarcinoma (ADC) is one of the major histological types of lung cancer. Genetic polymorphism in DNA repair genes and lung ADC susceptibility is well documented. In this case–control study, the association between the polymorphic sites of DNA repair genes XPD-751, XRCC1-399, and OGG1-326, and lung ADC susceptibility in ethnic Han Chinese population has been investigated. Genomic DNA was isolated from the peripheral blood of 201 healthy controls and 82 lung ADC patients from the people of Hunan Province, China. Polymorphisms of the investigated genes were analyzed by using polymerase chain reaction–restriction fragment length polymorphism. There was no significant difference between the samples from lung ADC patients and healthy controls about the genotype frequencies of XPD-751, XRCC1-399, and OGG1-326 sites. However, multifactor dimensionality reduction analysis showed that the genetic polymorphisms of the three-loci models of DNA repair genes (XPD-751/XRCC1-399/OGG1-326) are associated with lung ADC. Thus, this study reveals that a three-order interaction among the polymorphic sites of XPD-751, XRCC1-399, and OGG1-326 is associated with lung ADC risk in the studied population, although polymorphism in individual gene was not associated.

Tripartite motif containing 28 (TRIM28) promotes breast cancer metastasis by stabilizing TWIST1 protein

TRIM28 regulates its target genes at both transcriptional and posttranscriptional levels. Here we report that a TRIM28-TWIST1-EMT axis exists in breast cancer cells and TRIM28 promotes breast cancer metastasis by stabilizing TWIST1 and subsequently enhancing EMT. We find that TRIM28 is highly expressed in both cancer cell lines and advanced breast cancer tissues, and the levels of TRIM28 and TWIST1 are positively correlated with the aggressiveness of breast carcinomas. Overexpression and depletion of TRIM28 up- and down-regulates the protein, but not the mRNA levels of TWIST1, respectively, suggesting that TRIM28 upregulates TWIST1 post-transcriptionally. Overexpression of TRIM28 in breast cancer cell line promotes cell migration and invasion. Knockdown of TRIM28 reduces the protein level of TWIST1 with concurrent upregulation of E-cadherin and downregulation of N-cadherin and consequently inhibits cell migration and invasion. Furthermore, Immunoprecipitation and GST pull-down assays demonstrated that TRIM28 interacts with TWIST1 directly and this interaction is presumed to protect TWIST1 from degradation. Our study revealed a novel mechanism in breast cancer cells that TRIM28 enhances metastasis by stabilizing TWIST1, suggesting that targeting TRIM28 could be an efficacious strategy in breast cancer treatment.

Ubiquitination involved enzymes and cancer

Ubiquitination is a post-translational modification process that regulates multiple cell functions. It also plays important roles in the development of cancer. Mechanistically, ubiquitination is a complex process that is comprised of a series of events involving ubiquitin-activating enzymes, ubiquitin-conjugating enzymes and ubiquitin ligases. In general, covalent attachment of ubiquitin to the target proteins marks them for degradation. Dysregulation of the ubiquitination process may cause carcinogenesis. In this review, we summarize recent developments in understanding the relationship between ubiquitination enzymes and carcinogenesis.

ISG15 Inhibits IFN-α-Resistant Liver Cancer Cell Growth

Hepatocellular carcinoma (HCC) is one of the most prevalent tumors worldwide. Interferon-α (IFN-α) has been widely used in the treatment of HCC, but patients eventually develop resistance. ISG15 ubiquitin-like modifier (ISG15) is a ubiquitin-like protein transcriptionally regulated by IFN-α which shows antivirus and antitumor activities. However, the exact role of ISG15 is unknown. In the present study, we showed that IFN-α significantly induced ISG15 expression but failed to induce HepG2 cell apoptosis, whereas transient overexpression of ISG15 dramatically increased HepG2 cell apoptosis. ISG15 overexpression increased overall protein ubiquitination, which was not observed in cells with IFN-α-induced ISG15 expression, suggesting that IFN-α treatment not only induced the expression of ISG15 but also inhibited ISG15-mediated ubiquitination. The tumor suppressor p53 and p21 proteins are the key regulators of cell survival and death in response to stress signals such as DNA damage. We showed that p53 or p21 is only up regulated in HepG2 cells ectopically expressing ISG15, but not in the presence of IFN-α-induced ISG15. Our results suggest that ISG15 overexpression could be developed into a powerful gene-therapeutic tool for treating IFN-α-resistant HCC.

Genetic Identification and Molecular Modeling Characterization Reveal a Novel PROM1 Mutation in Stargardt4-like Macular Dystrophy

Stargardt disease-4 (STGD4) is an autosomal dominant complex, genetically heterogeneous macular degeneration/dystrophy (MD) disorder. In this paper, we used targeted next generation sequencing and multiple molecular dynamics analyses to identify and characterize a disease-causing genetic variant in four generations of a Chinese family with STGD4-like MD. We found a novel heterozygous missense mutation, c.734T>C (p.L245P) in the PROM1 gene. Structurally, this mutation most likely impairs PROM1 protein stability, flexibility, and amino acid interaction network after changing the amino acid residue Leucine into Proline in the basic helix-loop-helix leucine zipper domain. Molecular dynamic simulation and principal component analysis provide compelling evidence that this PROM1 mutation contributes to disease causativeness or susceptibility variants in patients with STGD4-like MD. Thus, this finding defines new approaches in genetic characterization, accurate diagnosis, and prevention of STGD4-like MD.