Xiao Feng Zhu

The pivotal role of c-Jun NH2-terminal kinase-mediated Beclin 1 expression during anticancer agents-induced autophagy in cancer cells

The c-Jun NH2-terminal kinase (JNK) pathway represents one subgroup of MAP kinases that are activated primarily by cytokines and exposure to environmental stress. Autophagy is a protein-degradation system characterized by the formation of double-membrane vacuoles termed autophagosomes. Autophagy-related gene beclin 1 plays a key role in autophagosome formation. However, the relationships between activation of JNK pathway, autophagy induction and Beclin 1 expression remain elusive. In this study, we used human cancer cell lines CNE2 and Hep3B to investigate the role of JNK-mediated Beclin 1 expression in ceramide-induced autophagic cell death. Ceramide-treated cells exhibited the characteristics of autophagy (that is, acidic vesicular organelle formation and the LC3-II generation). JNK was activated in these two cell lines exposed to ceramide and the phosphorylation of c-Jun also increased. In the meantime, we found that ceramide upregulated Beclin 1 expression in cancer cells. The upregulation of Beclin 1 expression could be blocked by SP600125 (a specific inhibitor of JNK) or a small interfering RNA (siRNA) directed against JNK1/2 or c-Jun. Chromatin immunoprecipitation and luciferase reporter analysis revealed that c-Jun was involved in the regulation of beclin 1 transcription in response to ceramide treatment. In addition, inhibition of JNK activity by SP600125 could inhibit autophagy induction by ceramide. Furthermore, Beclin 1 knockdown by siRNA also inhibited ceramide-mediated autophagic cell death. JNK-mediated Beclin 1 expression was also observed in topotecan-induced autophagy. These data suggest that activation of JNK pathway can mediate Beclin 1 expression, which plays a key role in autophagic cell death in cancer cells.

The expression of beclin 1 is associated with favorable prognosis in stage IIIB colon cancers.

Beclin-1 is a key modulator bridging autophagy, apoptosis and differentiation. This study investigated the expression of beclin-1 in human colon cancers and its association with clinicopathological characteristics. A total of 115 cases of cancer tissues with intact follow-up data were obtained from colon cancer patients with stage IIIB. The expression of beclin-1 in cancer nest and adjacent normal tissue was examined with immunohistochemistry. The results showed the immunostaining of beclin-1 was distributed in plasma-membrane, cytoplasm and nucleus in tumor cells, which occurred in 98 cases (85.2%) of the 115 patients. No or modest beclin-1 expression was observed in adjacent non-cancerous tissues. The higher level of beclin-1 expression strongly associated with longer survival. Both univariate analysis and multivariate analysis showed that the beclin-1 expression and invasive depth of primary mass (T stage) were independent prognostic factors. Additionally, there was no significant correlation of beclin-1 expression with clinicopathological characteristics, such as sex, age, site of primary mass, pathological classification, grade, and invasive depth with the nonparametric correlation Kendall’s tau-b test．Thus, it obviously manifests that beclin-1 is a favorable prognostic biomarker in locally advanced colon carcinomas and provides the information regarding the likely targeted therapy intervention.

Aurora-A, a Negative Prognostic Marker, Increases Migration and Decreases Radiosensitivity in Cancer Cells

Centrosomal Aurora-A (Aur-A) kinase ensures proper spindle assembly and accurate chromosome segregation in mitosis. Overexpression of Aur-A leads to centrosome amplification, aberrant spindle, and consequent genetic instability. In the present study, Aur-A was found to be overexpressed in laryngeal squamous cell carcinoma (LSCC). Moreover, Aur-A expression was adversely correlated with median survival, and further identified as a potential independent factor for disease prognosis. Suppression of Aurora kinase activity chemically or genetically led to LSCC Hep2 cell cycle arrest and apoptotic cell death. Importantly, we found that Aur-A increases cell migration and this novel function was correlated with Akt1 activation. The enhanced cell migration induced by Aur-A overexpression could be abrogated by either small-molecule Akt1 inhibitor or short interfering RNA. VX-680, a selective Aurora kinase inhibitor, decreased Akt1 phosphorylation at Ser(473) and inhibited cell migration, but failed to do so in constitutive active Akt1 (myr-Akt1)-overexpressed cells. Moreover, our data suggested that overexpression of Aur-A kinase might also contribute to radioresistance of LSCC. Inhibiting Aur-A by VX-680 induced expression of p53 and potently sensitized cells to radiotherapy, leading to significant cell death. Ectopic overexpression of Aur-A, however, reduced p53 level and rendered cells more resistant to irradiation. Taken together, we showed that Aur-A kinase, a negative prognostic marker, promotes migration and reduces radiosensitivity in laryngeal cancer cells.

Senescence and telomere shortening induced by novel potent G-quadruplex interactive agents, quindoline derivatives, in human cancer cell lines.

Agents stabilizing G-quadruplexes have the potential to interfere with telomere replication by blocking the elongation step catalysed by telomerase or telomerase-independent mechanism and could therefore act as antitumor agents. In this study, we found that quindoline derivatives interacted preferentially with intramolecular G-quadruplex structures and were novel potent telomerase inhibitors. Treatment with quindoline derivatives reproducibly inhibited telomerase activity in human leukemia K562 cells and colon cancer SW620 cells. N′-(10H-Indolo [3,2-b] quinolin-11-yl)-N, N-dimethyl-propane-1,3-diamine (SYUIQ-5), (one of quindoline derivatives), when added to K562 and SW620 cell culture at nonacute cytotoxic concentrations, increased time of population doublings of K562 and SW620 cells, induced a marked cessation in cell growth and cellular senescence phenotype after 35 and 18 days, respectively. Growth cessation was accompanied by a shortening of telomere length, and induction of p16, p21 and p27 protein expression. However, another compound SYUIQ-7 with greater IC50 for telomerase had no obvious cellular effect in nonacute cytotoxic concentrations. These results indicate that quindoline derivatives as novel potent G-quadruplex interactive agents induce senescence and telomere shortening in cancer cells and therefore are promising agents for cancer treatment.

Rhabdastrellic Acid-A Induced Autophagy-Associated Cell Death through Blocking Akt Pathway in Human Cancer Cells

Background Autophagy is an evolutionarily conserved protein degradation pathway. A defect in autophagy may contribute to tumorigenesis. Autophagy inducers could have a potential function in tumor prevention and treatment. Methodology/Principal Findings Our results showed that Rhabdastrellic acid-A, an isomalabaricane triterpenoid isolated from the sponge Rhabdastrella globostellata, inhibited proliferation of human cancer cell lines Hep3B and A549 and induced caspase-independent cell death in both the cell lines. Further investigation showed that Rhabdastrellic acid-A induced autophagy of cancer cells determined by YFP-LC3 punctation and increased LC3-II. The pretreatment with autophagy inhibitor 3-MA inhibited Rhabdastrellic acid-A-induced cell death. Knockdown of autophagy-related gene Atg5 inhibited Rhabdastrellic acid-A-induced cell death in A549 cells. Also, phospho-Akt and its downstream targets significantly decreased after treatment with Rhabdastrellic acid-A in both cancer cell lines. Transfection of constitutive active Akt plasmid abrogated autophagy and cell death induced by Rhabdastrellic acid-A. Conclusions/Significance These results suggest that Rhabdastrellic acid-A could induce autophagy-associated cell death through blocking Akt pathway in cancer cells. It also provides the evidence that Rhabdastrellic acid-A deserves further investigation as a potential anticancer or cancer preventive agent.

Inhibition of Aurora-A suppresses epithelial-mesenchymal transition and invasion by downregulating MAPK in nasopharyngeal carcinoma cells

Mitotic serine/threonine kinase Aurora-A (Aur-A) plays a critical role in regulating centrosome segregation and spindle assemble. Aur-A overexpression causes excessive centrosome duplication and abnormal spindle structure, leading to tumor malignant progression. Here, we investigated Aur-A expression in nasopharyngeal carcinoma (NPC) and the association between Aur-A and NPC invasiveness. We showed that overexpression of Aur-A in tumor tissues was correlated with cranial bone invasion and clinical stage in NPC patients. Suppression of Aur-A by either selective Aurora inhibitory VX-680 or small-interfering RNA caused G(2)/M arrest and apoptotic cell death in NPC CNE-2 cells. Significantly, inhibition of Aur-A suppressed CNE-2 cell invasion and restored membrane expression of epithelial markers, E-cadherin and beta-catenin, suggesting a reversed epithelial-mesenchymal transition process in cancer cells. In addition, we found that Aur-A-regulated epithelial-mesenchymal transition and invasion were mediated by mitogen-activated protein kinase (MAPK) phosphorylation. Moreover, suppression of MAP kinase by small-interfering RNA or its upstream MEK1/2-selective inhibitor U0126 abrogated cell invasion enhanced by Aur-A overexpression. On the other hand, forced overexpression of constitutively active form of MEK1/2, MEK2DD, in CNE-2 cancer cells rescued cell invasive ability suppressed by VX-680-imposed Aur-A inhibition. Our results indicated that Aur-A acted through a downstream MAP kinase pathway to promote epithelial-mesenchymal transition and invasiveness in nasopharyngeal tumorigenesis. Small chemical inhibitor VX-680 may offer as a promising molecular targeting agent in human NPC.

PKB/Akt promotes DSB repair in cancer cells through upregulating Mre11 expression following ionizing radiation

An elevated DNA-repair capacity in cancer cells leads to radiation resistance and severely limits the efficacy of radiation therapy. Activation of Akt is tightly associated with resistance to radiotherapy, and Mre11 protein has important role during the repair of DNA double-strand breaks (DSBs). In this report, our results showed that inhibition of Akt activity impaired the repair of DSBs in CNE2 cells, whereas activated Akt promoted the repair of DSBs in HeLa cells. Knockdown of Mre11 also impaired the process of DSB repair in both these two cell lines. More importantly, we found that Akt could regulate Mre11 expression. Inhibition of Akt activity by small interfering RNA or LY294002 efficiently downregulated the Mre11 expression in CNE2 cells, and transfection with myr-Akt plasmid in HeLa cells upregulated the Mre11 expression. In addition, luciferase reporter analysis revealed that Mre11 reporter activity increased after transfection with myr-Akt1 plasmids, and this myr-Akt1-induced transcriptional activity was blocked in the presence of LY294002. Further study showed GSK3β/β-catenin/LEF-1 pathway was involved in this regulation. Knockdown of β-catenin or LEF-1 led to the downregulation of Mre11, whereas overexpression of β-catenin led to upregulation of Mre11. The chromatin immunoprecipitation assay assay showed β-catenin/LEF-1 heterodimer could directly bind to the promoter of Mre11 in vivo. And the luciferase activity of the pGL3-Mre11 and pGL3-Lef increased in HeLa cells following β-catenin plasmid co-transfected, but was abolished when the LEF-1-binding conserved sequences of Mre11 promoter were mutated. These results together support Akt can upregulate the expression of Mre11 through GSK3β/ β-catenin/LEF pathway to elevate DSB-repair capacity in cancer cells.

Acetylcholinesterase expression mediated by c-Jun-NH2-terminal kinase pathway during anticancer drug-induced apoptosis

It has been shown that acetylcholinesterase (AChE) expression was induced during apoptosis and the anti-sense oligonucleotides and siRNA of AChE may prevent apoptosis in various cell types. However, the mechanisms underlying AChE upregulation remain elusive. We demonstrated here that c-Jun NH2-terminal kinase (JNK) could mediate AChE expression. In this study, both etoposide and excisanin A, two anticancer agents, induced apoptosis in colon cancer cell line SW620 as determined by Annexin V staining, the cleavage of caspase-3 and the proteolytic degradation of poly (ADP-ribose) polymerase (PARP). The results showed that both the agents upregulated AChE in SW620 cells. In the meantime, JNK was also activated and the expression and phosphorylation of c-Jun increased in SW620 cells exposed to the two agents. The induced AChE mRNA and protein expression could be blocked by SP600125, a specific inhibitor of SAPK/JNK, and small interfering RNA directed against JNK1/2. Transfection with adenovirus-mediated dominant negative c-Jun also blocked the upregulation of AChE expression. Together, these results suggest that AChE expression may be mediated by the activation of JNK pathway during apoptosis through a c-Jun-dependent mechanism.

Beclin 1 expression: A predictor of prognosis in patients with extranodal natural killer T-cell lymphoma, nasal type

Beclin 1 plays an important role in autophagy, differentiation, antiapoptosis and the development and progression of cancer. The function and expression of Beclin 1 in natural killer T-cell lymphoma is largely unexplored. The study aimed to investigate Beclin 1 expression and its relationship with prognosis in extranodal natural killer T-cell lymphoma, nasal-type (ENKL). Beclin 1 protein expression in 65 tumor specimens from patients newly diagnosed with ENKL was examined by immunohistochemistry (IHC). The clinical significance of Beclin 1 in ENKL was statistically analyzed. Immunopositivity for Beclin 1 was found in 56 (86.2%) of the 65 samples. Low Beclin 1 expression was significantly associated with advanced Ann Arbor stage, intermediate to high IPI risk and elevated LDH level. Low Beclin 1 expression was associated with worse overall survival (OS; p = 0.001) and progression-free survival (PFS; p = 0.017). In multivariate analysis, Beclin 1 expression, advanced Ann Arbor stage and B symptoms were found to be independent prognostic factors of OS and PFS. Consequently, a new clinico-pathological prognostic model was proposed. The model could discriminate different survival outcomes between low risk and high risk groups based on OS and PFS (p < 0.0001, respectively). Beclin 1 expression is predictive of prognosis in ENKL. The new clinico-pathological prognostic model may be help identify patients with different clinical outcomes.

Intensive expression of UNC-51-like kinase 1 is a novel biomarker of poor prognosis in patients with esophageal squamous cell carcinoma

The serine/threonine kinase UNC‐51‐like kinase 1 (ULK1) plays an essential role in autophagosome formation, although the exact molecular mechanism is unknown. The present study was first to investigate the clinical and prognostic significance of ULK1 in esophageal squamous cell carcinoma (ESCC). Protein and mRNA levels of ULK1 in normal esophageal epithelial cells, ESCC cell lines, paired ESCC lesions and the adjacent noncancerous tissues were examined using western blot and real‐time RT‐PCR. The results showed that only the ULK1 protein level was upregulated in ESCC samples compared with normal esophageal cells and tissues. Also, we found that protein stabilization of ULK1 was higher in ESCC cell lines. Furthermore, immunohistochemical staining of ULK1 was performed on the tissue microarray containing 248 ESCC and 51 normal esophageal tissues. A total of 70.2% ESCC specimens showed intensive expression of ULK1 in contrast to the undetectable expression of ULK1 in normal esophageal tissues. Statistical analysis revealed that ULK1 expression was significantly correlated with T status (P = 0.048). Moreover, patients with higher ULK1 expression were associated with shorter overall survival time. Multivariate analysis suggested that ULK1 expression and N status (P < 0.001) were independent prognostic indicators for the survival of patients. Functional studies showed that suppression of ULK1 expression in ESCC cell lines by specific small interfering RNA resulted in inhibition of cell proliferation and induction of apoptosis under starvation conditions. These findings provide evidence that ULK1 represents a novel and clinically useful biomarker for ESCC patients and plays an important role during the progression of ESCC. (Cancer Sci 2011; 102: 1568–1575)