Insight into mechanism of oxidative DNA damage in angiomyolipomas from TSC patients.
BACKGROUND
The tuberous sclerosis complex (TSC) is caused by defects in one of two tumor suppressor genes, TSC-1 or TSC-2. TSC-2 gene encodes tuberin, a protein involved in the pathogenesis of kidney tumors, both angiomyolipomas and renal cell carcinomas. Loss of heterozygosity at the 8-oxoG-DNA glycosylase (OGG1) allele is found in human kidney clear cell carcinoma identifying loss of OGG1 function as a possible contributor to tumorigenesis in the kidney. Tuberin regulates OGG1 through the transcription factor NF-YA in cultured cells. The purpose of this study is to determine the effect of tuberin-deficiency on OGG1 protein and mRNA levels as well as on 8-oxodG levels in kidney tumors from patients with TSC. In addition we evaluated the phophorylation level of downstream targets of mTOR, phospho-S70K, in kidney tumor tissue from TSC patients.


RESULTS
Kidney angiomyolipoma tissue from TSC patients expresses significant levels of phopho-tuberin and low levels of tuberin compared to control kidney tissue. The increase in tuberin phosphorylation and the decrease tuberin expression are associated with decrease in OGG1 protein and mRNA levels in tumor samples compared to normal kidney samples. The decrease OGG1 expression is also associated with significant decrease in the transcription factor, NF-YA, expression in tumor samples compared to normal tissues. In addition, the levels of 8-oxodG are 4-fold higher in tumors compared to control samples. The significant increase of phospho-tuberin expression is associated with increase phosphorylation of S6K in tumor samples compared to controls. Cyclin D1 expression is also 3-fold higher in increase in the tumor tissues compared to normal kidney tissues.


CONCLUSIONS
These data indicate that tuberin deficiency in angiomyolipoma enhances mTOR activation by phosphorylation of S6K and downregulation of protein and mRNA expression of OGG1 resulted in accumulation of oxidized DNA in patients with TSC. These data suggest that tuberin and OGG1 are important proteins in the pathogenesis of angiomyolipoma in TSC patients.
Habib
Samy L
SL
Geriatric Research Education and Clinical Center, South Texas Veterans Healthcare System, San Antonio, TX, USA. habib@uthscsa.edu
D000080242:8-Hydroxy-2'-Deoxyguanosine; D018207:Angiomyolipoma / Q000235:genetics* / Q000378:metabolism*; D000818:Animals; D023081:CCAAT-Binding Factor / Q000378:metabolism; D002460:Cell Line; D019938:Cyclin D1 / Q000378:metabolism; D004249:DNA Damage / Q000235:genetics / Q000502:physiology*; D045647:DNA Glycosylases / Q000235:genetics / Q000378:metabolism*; D003849:Deoxyguanosine / Q000031:analogs & derivatives / Q000378:metabolism; D006801:Humans; D015151:Immunoblotting; D066298:In Vitro Techniques; D007668:Kidney / Q000378:metabolism / Q000473:pathology; D051379:Mice; D018384:Oxidative Stress; D010766:Phosphorylation; D011494:Protein Kinases / Q000378:metabolism; D051381:Rats; D020133:Reverse Transcriptase Polymerase Chain Reaction; D058570:TOR Serine-Threonine Kinases; D014402:Tuberous Sclerosis / Q000235:genetics* / Q000378:metabolism*; D000077005:Tuberous Sclerosis Complex 2 Protein; D025521:Tumor Suppressor Proteins / Q000378:metabolism / Q000502:physiology
D023081:CCAAT-Binding Factor; C492061:NFYA protein, human; C000624653:TSC2 protein, human; D000077005:Tuberous Sclerosis Complex 2 Protein; D025521:Tumor Suppressor Proteins; D019938:Cyclin D1; D000080242:8-Hydroxy-2'-Deoxyguanosine; D011494:Protein Kinases; C546842:MTOR protein, human; C546843:mTOR protein, mouse; D058570:TOR Serine-Threonine Kinases; D045647:DNA Glycosylases; C479058:oxoguanine glycosylase 1, human; D003849:Deoxyguanosine