MG-132 Inhibits Telomerase Activity, Induces Apoptosis and G₁ Arrest Associated with Upregulated p27kip1 Expression and Downregulated Survivin Expression in Gastric Carcinoma Cells

Abstract

Ubiquitin-proteasome pathway (UPP) is the major system for the selective degradation of cellular proteins that play key roles in cellular processes. Previous study indicated that ubiquitin-proteasome inhibitor MG-132 could inhibit growth of some carcinoma. However, anti-carcinoma mechanism of MG-132 is unclear. Our objective was to investigate mechanisms of growth inhibitory effect of MG-132 on gastric carcinoma cells. Gastric carcinoma cell SGC-7901 was treated with ubiquitin-proteasome inhibitor MG-132. Cell growth suppression was evaluated with 3-(4,5-dimethylthiazole-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) assay. DNA synthesis was evaluated by ³H-thymidine (³H-TdR) incorporation. Activity of telomerase was examined by telomeric repeat amplification protocol (TRAP) PCR-ELISA. Cell cycle and apoptosis were detected by flow cytometry (FCM). DNA fragment analysis was used to confirm the presence of apoptosis. Expression of p27kip1 and survivin was detected using the western blot method. After exposed to MG-132, the growth and value of ³H-TdR incorporation of gastric carcinoma cells were obviously inhibited. TRAP PCR-ELISA showed that light absorption of cells gradually decreased after exposed to 5 μ M of MG-132 for 24, 48, 72 and 96 h (P < 0.01). The percentage of cells at G₀/G₁ phase was increased and that at S and G₂/M phase was decreased (P < 0.01). The ratio of apoptotic cells treated with 5 μ M MG-132 for 96 h was 53.7 ± 6.4%. Agarose electrophoresis showed marked ladders. Moreover, expression of p27kip1 of cells was increased and expression of survivin was decreased. Our results suggest that MG-132 inhibits telomerase activity, induces apoptosis and G₁ arrest which is associated with upregulated p27kip1 expression and downregulated survivin expression in gastric carcinoma cells.

Keywords:

• Ubiquitin-proteasome
• Gastric carcinoma cell
• Telomerase
• Apoptosis
• P27kip1
• Survivin