Translational research in gastric malignancy

CDK5 suppresses the metastasis of gastric cancer cells by interacting with and regulating PP2A

Several previous studies have demonstrated that cyclin‑dependent kinase (CDK)‑5 expression serves an important role in promoting the development of malignant tumours. We have previously reported that CDK5 suppresses gastric tumourigenesis. The aim of the present study was to investigate the mechanistic basis of CDK5. The results of immunoprecipitation and western blot analysis demonstrated that CDK5 could interact with serine/threonine‑protein phosphatase 2A (PP2A). The use of an inhibitor of PP2A in CDK5‑overexpressing gastric cancer (GC) cell lines antagonized CDK5‑mediated suppression in GC cells. Further analysis revealed that PP2A expression was downregulated in GC and patients with low levels of PP2A had worse survival outcomes than those with high levels of PP2A (P=0.035). Therefore, the present study provided a novel mechanism for CDK5‑mediated tumour suppression, suggesting that CDK5 may be an attractive target for future therapeutic strategies for treating GC. In addition, low levels of PP2A may indicate a tendency for poor prognosis in patients with GC.

Dietary Intervention of Artemisia and Green Tea Extracts to Rejuvenate Helicobacter pylori-Associated Chronic Atrophic Gastritis and to Prevent Tumorigenesis

OBJECT

As nonmicrobial dietary approach is capable of controlling Helicobacter pylori infection, we evaluated the efficacy of long-term dietary administration of Artemisia and/or green tea extracts on H. pylori-initiated, high-salt-promoted chronic atrophic gastritis and gastric tumorigenesis mouse model.

METHODS

Helicobacter pylori-infected and high-salt-diet-administered C57BL/6 mice were administered with Artemisia extracts (MP group) and/or green tea extracts (GT group) for 36 weeks in addition to the control group (ES group, gastroprotective drug, ecabet sodium 30 mg/kg, diet pellet). Gross and pathological gastric lesions were evaluated after 24 and 36 weeks, respectively, and their underlying molecular changes were measured in gastric homogenates. Detailed mechanisms were further evaluated in in vitro cell models.

RESULTS

The erythematous and nodular changes and mucosal ulcerative and erosive lesions were noted in the control group at 24 weeks. MP, GT, MPGT, and ES groups all showed significantly ameliorated pathologic lesion compared to the control group (p < .05). After the 36 weeks, scattered nodular masses with some central ulcers and thin gastric surface were noted in the control stomach, whereas no tumorous lesion and milder atrophic changes were observed in all MP, GT, and MPGT groups except ES group (p < .05). On molecular analysis, increased expressions of COX-2, TNF-α, IL-6, lipid peroxide, and activated STAT3 relevant to H. pylori infection were significantly decreased with MPGT administration (p < .01), whereas HSP70 was significantly increased. PGDH expressions, core tumor suppressor involved in carcinogenesis, were significantly decreased with H. pylori infection (p < .05), but significantly increased in MPGT group (p < .05). Increased mucosal apoptotic index noted in the control group was significantly decreased with MP and/or GT along with significantly preserved gastric gastroprotective mediators (p < .01) such as mucins, HSP27, and HSP70. H. pylori-induced serum TNF-α and NF-κB activations were significantly decreased with MPGT administration (p < .05).

CONCLUSION

Long-term dietary intake of MP and/or GT can be an effective strategy either to rejuvenate H. pylori atrophic gastritis or to suppress tumorigenesis.

Cyclin-dependent kinase 5 decreases in gastric cancer and its nuclear accumulation suppresses gastric tumorigenesis

PURPOSE

As a cyclin-independent atypical CDK, the role of CDK5 in regulating cell proliferation in gastric cancer remains unknown.

EXPERIMENTAL DESIGN

Expression of CDK5 in gastric tumor and paired adjacent noncancerous tissues from 437 patients was measured by Western blotting, immunohistochemistry, and real-time PCR. The subcellular translocation of CDK5 was monitored during gastric cancer cell proliferation. The role of nuclear CDK5 in gastric cancer tumorigenic proliferation and ex vivo xenografts was explored. Furthermore, by screening for compounds in the PubChem database that disrupt CDK5 association with its nuclear export facilitator, we identified a small molecular (NS-0011) that inhibits gastric cancer cell growth.

RESULTS

CDK5 level was significantly decreased in the majority of gastric tumor tissues, and the reduction of CDK5 correlated with the severity of gastric cancer based on tumor and lymph node metastasis and patient 5-year fatality rate. Nuclear localization of CDK5 was found to be significantly decreased in tumor tissues and gastric cancer cell lines, whereas exogenously expression of nucleus-targeted CDK5 inhibited the proliferation and xenograft implantation of gastric cancer cells. Treatment with the small molecule NS-0011, which increases CDK5 accumulation in the nucleus, suppressed both cancer cell proliferation and xenograft tumorigenesis.

CONCLUSIONS

Our results suggest that low CDK5 expression is associated with poor overall survival in patients with gastric cancer, and nuclear accumulation of CDK5 inhibits the proliferation and tumorigenicity of human gastric cancer cells.

Critical role and regulation of transcription factor FoxM1 in human gastric cancer angiogenesis and progression

The mammalian forkhead box (Fox) transcription factor FoxM1b is implicated in tumorigenesis. However, the presence of expression and role of FoxM1b in gastric cancer remain unknown. Therefore, we investigated FoxM1b expression in 86 cases of primary gastric cancer and 57 normal gastric tissue specimens. We further investigated the underlying mechanisms of altered FoxM1b expression in and the effect of this altered expression on gastric cancer growth and metastasis using in vitro and animal models of gastric cancer. We found weak expression of FoxM1b protein in the mucous neck region of gastric mucosa, whereas we observed strong staining for FoxM1b in tumor cell nuclei in various gastric tumors and lymph node metastases. A Cox proportional hazards model revealed that FoxM1b expression was an independent prognostic factor in multivariate analysis (P < 0.001). Experimentally, overexpression of FoxM1b by gene transfer significantly promoted the growth and metastasis of gastric cancer cells in orthotopic mouse models, whereas knockdown of FoxM1b expression by small interfering RNA did the opposite. Promotion of gastric tumorigenesis by FoxM1b directly and significantly correlated with transactivation of vascular endothelial growth factor expression and elevation of angiogenesis. Given the importance of FoxM1b to regulation of the expression of genes key to cancer biology overall, dysregulated expression and activation of FoxM1b may play important roles in gastric cancer development and progression.