Expression of mitochondrial genes and DNA-repair-related nuclear genes is altered in xeroderma pigmentosum fibroblasts

Abstract

Differential hybridization was used to detect repair defects in xeroderma pigmentosum (XP) that are not amenable to current analyses. cDNA libraries were constructed from cytoplasmic RNA of normal and XP fibroblast strains (complementation groups A and D) and analyzed for differential gene expression. More than 40,000 lambda gt10 cDNA clones were differentially screened with in vitro transcripts made from cDNA in the pBluescript vector. Six differential clones were detected in the libraries of the XP group A and D strains which caused stronger or weaker signals when probed with transcripts from XP strains than with those from the normal strains. Two clones coded for mitochondrial genes: mitochondrial 16 S rRNA and ATPase 6L. Overexpression of mitochondrial genes in XP may indicate that functions of the ATP-generating system are impaired since such functions are intensified whenever they become insufficient, for example as a consequence of DNA damage. It is tempting to assume that abnormal mitochondria are one of the causes for the neurological malfunctions in XP. Furthermore, densitometric analysis of Northern blots revealed that mRNA of lactate dehydrogenase, chain M, was less abundant in four XP group A strains (extent of reduction: 70%) and in two XP group D strains (extent of reduction: 58%). Enzyme activity was also diminished. In addition, mRNA of the gene for glyceraldehyde-3-phosphate dehydrogenase was less expressed in the same XP group A and D fibroblast strains investigated (reduction in both complementation groups: 50%). Both glycolytic enzymes have nuclear functions apart from their role in sugar metabolism. Lactate dehydrogenase, chain M, is identical to a helix-destabilizing protein; it is closely associated with chromatin and unfolded DNA, suggesting a role in DNA synthesis and transcription. The 37-kDa subunit of glyceraldehyde-3-phosphate dehydrogenase is involved in transcription and was shown to be identical to uracil-DNA glycosylase, a base-excision repair enzyme. We presume that the nuclear functions of these glycolytic enzymes may be thwarted in the XP strains investigated and may account for malfunctions in XP, particularly for neurological disturbances.

Oxidative Stress and Mitochondrial Dysfunction across Broad-Ranging Pathologies: Toward Mitochondria-Targeted Clinical Strategies

“…Mitochondrial abnormalities were exhibited in terms of defective mitochondrial gene transcripts for 16 S rRNA, ATPase 6L, and lactate dehydrogenase; moreover, lower-than-normal CoQ10 levels were observed in serum from XP patients [74–77]. …”

Human DNA repair genes

“…The human CRY1 and CRY2 genes were isolated on the basis of their similarity to the D. melanogaster photolyase genes, but their protein products apparently have no photolyase activity on either 6-4PPs or cyclobutane pyrimidine dimers (CPDs); instead, they are believed to perform different functions as light-independent components of the circadian clock Griffin et al, 1999]. Another example is that of the gene for human nuclear uracil-DNA glycosylase, HNG, which was isolated by screening a human cDNA library with the help of monoclonal antibodies against human uracil-DNA glycosylase, but subsequently found to be identical to GAPD, whose product is involved (perhaps in a different multimeric form) in carbohydrate metabolism, where it catalyzes the oxidative phosphorylation of glyceraldehyde-3-phosphate Mansur et al, 1993;Xia et al, 1994;Baxi and Vishwanatha, 1995], and in translational control of gene expression.…”

Enhanced Expression of The LDH-A Gene after Gravity-changing Stress in Human RSa Cells.

“…Interestingly, LDH has been suggested to reside in nuclei of mammalian cells, to bind to single-stranded DNA and to exert functions in DNA replication, transcription and repair (Calissano et al, 1985;Grosse et al, 1986;Xia et al, 1994). Further, Popanda et al reported that LDH stimulated UV-induced DNA repair in human fibroblasts (Popanda et al, 1998).…”