Analysis of mechanism of the induction of apoptosis induced by the toxin derived form periodontopathic bacteria and its intracellular signal transduction

伴放线放线杆菌产生的致死性膨胀毒素（CDT）可使Hela细胞周期阻滞于G2/M期。在本研究中，我们证明，从放线放线菌共生放线菌的CDT诱导的B细胞杂交瘤细胞株，HS-72的G2期细胞周期阻滞通过流式细胞术分析。使用HS-72细胞研究CDT诱导的细胞周期阻滞的机制。CDT上调细胞周期蛋白依赖性激酶抑制剂p21 CIP 1/WAF 1和抑癌蛋白p53的表达。异位表达的人乳头瘤病毒16型E6/E7取消了CDT诱导的p53的表达。E6/E7的表达对CDT诱导的HS-72细胞p21 CIP 1/WAF 1表达及G2期阻滞无影响，而adominant negative p53突变体的过表达对CDT诱导的HS-72细胞p21 CIP 1/WAF 1表达及G2期阻滞无影响。这些结果表明，来自伴放线菌的CDT通过p53非依赖性途径诱导B谱系细胞中的p21 CIP 1/WAF 1表达和G2细胞周期停滞。结合对伴放线菌CDT诱导的Hela和COS-1细胞的进一步观察，本研究的结果表明，CDT诱导的p21 CIP 1/WAF 1可能促进了大肠杆菌细胞的G2期阻滞。

The cytolethal distending toxin (CDT) from Actinobacillus actinomycetemcomitans was previously shown to induce cell cycle arrest in G2/M phase in Hela cells. In the present study, we demonstrated that the CDT from A.actinomycetemcomitans induced G2 cell cycle arrest in the B cell hybridoma cell line, HS-72 by flow cytometric analysis. The mechanism of CDT-induced cell cycle arrest was investigated using HS-72 cells. The CDT up-regulated the expression of cyclin-dependent kinase inhibitor p21CIP1/WAF1 and tumor-suppressor protein p53. The ectopic expression of human papilloma virus type-16 E6/E7 abolished the CDT-induced expression of p53. However, E6/E7 expression had no effect on the expression of p21CIP1/WAF1 and G2 cell cycle arrest in HS-72 cells cultured with the CDT.Furthermore, overexpression of adominant negative p53 mutant did not inhibit the CDT-mediated p21CIP1/WAF1 expression and G2 cell cycle arrest in HS-72 cells. These results indicate that the CDT from A.actinomycetemcomitans induce p21CIP1/WAF1 expression and G2 cell cycle arrest in B lineage cells by p53-independent pathways. Together with additional observations on Hela and COS-1 cells cultured with the CDT from A.actinomycetemcomitans, the results in the present study suggest the CDT-induced p21CIP1/WAF1 may promote G2 cell cycle arrest in mammmalian cells.