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Deletion and point (L166P) mutations of DJ-1 have recently been shown to be responsible for the onset of familial Parkinson's disease (PD, PARK7). The aim of this study was to determine the role of DJ-1 in PD. We first found that DJ-1 eliminated hydrogen peroxide in vitro by oxidizing itself. We then found that DJ-1 knockdown by short interfering RNA rendered SH-SY5Y neuroblastoma cells susceptible to hydrogen peroxide-, MPP þ -or 6-hydroxydopamine-induced cell death and that cells harbouring mutant forms of DJ-1, including L166P, became susceptible to death in parallel with the loss of oxidized forms of DJ-1. These results clearly showed that DJ-1 has a role in the antioxidative stress reaction and that mutations of DJ-1 lead to cell death, which is observed in PD.

Telomerase activation is thought to be a critical step in cellular immortalization and carcinogenesis. The human telomerase catalytic subunit (hTERT) is a rate limiting determinant of the enzymatic activity of human telomerase. In the previous study, we identified the proximal 181 bp core promoter responsible for transcriptional activity of the hTERT gene. To identify the regulatory factors of transcription, transient expression assays were performed using hTERT promoter reporter plasmids. Serial deletion assays of the core promoter revealed that the 5'-region containing the E-box, which binds Myc/Max, as well as the 3'-region containing the GC-box, which binds Sp1, are essential for transactivation. The mutations introduced in the E-box or GC-box significantly decreased transcriptional activity of the promoter. Overexpression of Myc/Max or Sp1 led to significant activation of transcription in a cell type-specific manner, while Mad/Max introduction repressed it. However, the effects of Myc/Max on transactivation were marginal when Sp1 sites were mutated. Western blot analysis using various cell lines revealed a positive correlation between c-Myc and Sp1 expression and transcriptional activity of hTERT. Using fibroblast lineages in different stages of transformation, we found that c-Myc and Sp1 were induced to a dramatic extent when cells overcame replicative senescence and obtained immortal characteristics, in association with telomerase activation. These findings suggest that c-Myc and Sp1 cooperatively function as the major determinants of hTERT expression, and that the switching functions of Myc/Max and Mad/Max might also play roles in telomerase regulation.

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