Enhanced mitochondrial DNA repair and cellular survival after oxidative stress by targeting the human 8-oxoguanine glycosylase repair enzyme to mitochondria.

Oxidative damage to mitochondrial DNA (mtDNA) has been implicated as a causative factor in many disease processes and in aging. We have recently discovered that different cell types vary in their capacity to repair this damage, and this variability correlates with their ability to withstand oxidative stress. To explore strategies to enhance repair of oxidative lesions in mtDNA, we have constructed a vector containing a mitochondrial transport sequence upstream of the sequence for human 8-oxoguanine DNA glycosylase. This enzyme is the glycosylase/AP lyase that participates in repair of purine lesions, such as 8-oxoguanine. Western blot analysis confirmed that this recombinant protein was targeted to mitochondria. Enzyme activity assays showed that mitochondrial extracts from cells transfected with the construct had increased enzyme activity compared with cells transfected with vector only, whereas nuclear enzyme activity was not changed. Repair assays showed that there was enhanced repair of oxidative lesions in mtDNA. Additional studies revealed that this augmented repair led to enhanced cellular viability as determined by reduction of the tetrazolium compound to formazan, trypan blue dye exclusion, and clonogenic assays. Therefore, targeting of DNA repair enzymes to mitochondria may be a viable approach for the protection of cells against some of the deleterious effects of oxidative stress.

Interaction of the chicken progesterone receptor with heat shock protein (HSP) 90.

The chicken progesterone receptor A (PRA) was expressed from cDNA by in vitro transcription and translation and also by transient transfection of receptor-negative COS M6 cells. These receptors synthesized from cDNA exhibited functional properties similar to those of oviduct PRA. The ability of PRA to form an 8S complex and to bind to DNA was studied. PRA, synthesized by either expression system, formed an 8S complex which was dissociated by incubation in vitro with 0.4 M NaCl or 20 nM progesterone to generate a 4S species able to bind to DNA-cellulose. The presence of HSP 90 in the PRA 8S complex was confirmed by use of an HSP 90-specific antibody, AC-7. Expression constructs coding for various receptor deletions were studied in order to identify the site of interaction of PRA with HSP 90. Deletions of 290 amino acids from the C-terminus resulted in the loss of ability to form an 8S complex. Truncated receptor proteins lacking 153 amino acids from the C-terminus or 369 amino acids from the N-terminus were able to interact with HSP 90. These data suggest that the site of interaction between PRA and HSP 90 responsible for 8S complex formation may be in this region (amino acid 369-506). However, small internal amino acid deletions in this region of PRA did not result in the loss of interaction of mutant receptor proteins with HSP 90. Thus, it appears that there may be more than one site of interaction between PRA and HSP 90 in this region.