Quantitative TP73 transcript analysis in hepatocellular carcinomas.
OBJECTIVE
The p53 family member p73 displays significant homology to p53, but data from primary tumors demonstrating increased expression levels of p73 in the absence of any gene mutations argue against a classical tumor suppressor function. A detailed analysis of the p73 protein in tumor tissues has revealed expression of two classes of p73 isoforms. Whereas the proapoptotic, full-length, transactivation-competent p73 protein (TA-p73) has a putative tumor suppressor activity similar to p53, the antiapoptotic, NH(2)-terminally truncated, transactivation-deficient p73 protein (DeltaTA-p73) has been shown to possess oncogenic activity. The oncogenic proteins can be generated by the following two different mechanisms: (a) aberrant splicing (p73Deltaex2, p73Deltaex2/3, DeltaN'-p73) and (b) alternative promoter usage of a second intronic promoter (DeltaN-p73). The purpose of our study was to elucidate the origin of DeltaTA-p73 isoforms in hepatocellular carcinomas.


METHODS
We analyzed the underlying mechanisms of p73 overexpression in cancer cells by quantification of p73 transcripts from 10 hepatocellular carcinoma patients using isoform-specific real-time reverse transcription-PCR.


RESULTS
Our data demonstrate that only aberrantly spliced DeltaTA-p73 transcripts from the TA promoter show significantly increased expression levels in the tumor whereas the DeltaN-p73 transcript generated from the second promoter is not significantly up-regulated.


CONCLUSIONS
Although we only analyzed 10 patient samples the results strongly suggest that the elevated activity of the first promoter (TA promoter) accounts for high-level expression of both full-length TA-p73 and aberrantly spliced DeltaTA-p73 isoforms in hepatocellular carcinoma tissues.
Stiewe
Thorsten
T
Center for Cancer Research and Cancer Therapy, Institute of Molecular Biology, University of Essen Medical School, Essen, Germany.
Tuve
Sebastian
S
Peter
Martin
M
Tannapfel
Andrea
A
Elmaagacli
Ahmet H
AH
Pützer
Brigitte M
BM
D000368:Aged; D017209:Apoptosis; D006528:Carcinoma, Hepatocellular / Q000378:metabolism* / Q000473:pathology; D045744:Cell Line, Tumor; D004268:DNA-Binding Proteins / Q000096:biosynthesis*; D005091:Exons; D005260:Female; D016147:Genes, Tumor Suppressor; D006801:Humans; D007438:Introns; D008113:Liver Neoplasms / Q000378:metabolism*; D019656:Loss of Heterozygosity; D008297:Male; D008875:Middle Aged; D008957:Models, Genetic; D009154:Mutation; D009687:Nuclear Proteins / Q000096:biosynthesis*; D010957:Plasmids / Q000378:metabolism; D011401:Promoter Regions, Genetic; D020033:Protein Isoforms; D017434:Protein Structure, Tertiary; D012313:RNA / Q000378:metabolism; D012326:RNA Splicing; D012333:RNA, Messenger / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D013696:Temperature; D013997:Time Factors; D015533:Transcriptional Activation; D000072160:Tumor Protein p73; D016159:Tumor Suppressor Protein p53 / Q000378:metabolism; D025521:Tumor Suppressor Proteins; D015854:Up-Regulation
D004268:DNA-Binding Proteins; D009687:Nuclear Proteins; D020033:Protein Isoforms; D012333:RNA, Messenger; C000606460:TP73 protein, human; D000072160:Tumor Protein p73; D016159:Tumor Suppressor Protein p53; D025521:Tumor Suppressor Proteins; D012313:RNA