A novel peroxisome proliferator-activated receptor gamma isoform with dominant negative activity generated by alternative splicing.
We examined the peroxisome proliferator-activated receptor gamma (PPARG) locus in an attempt to identify expressed sequence tags and/or conserved non-coding sequences in the intron sequences containing open reading frames and potentially able to encode new proteins. We identified a new PPARG transcript, defined gammaORF4, which harbors a readthrough in intron 4. The expected translated protein lacks the ligand-binding domain encoded by exons 5 and 6. We identified the transcript in human tumor cell lines and tissues, synthesized the cDNA, and cloned it in expression vectors. Using transient transfections, we found that gammaORF4 cDNA is translated into a predominantly nuclear protein that does not transactivate a reporter gene. Moreover, the isoform is dominant negative versus PPARgamma. Interestingly, gammaORF4 was expressed in vivo in a series of sporadic colorectal cancers. In some cases, it was expressed, albeit at lower levels, also in the mucosa adjacent to the tumors, suggesting that it may be related to tumorigenesis. A tumorigenic effect of gammaORF4 is in line with our finding that gammaORF4 has not only lost the capacity to restrain cell growth but has acquired the potential to stimulate it. In conclusion, this study demonstrates that gammaORF4 is expressed in vivo, that it has lost some PPARgamma properties, and that it affects PPARgamma functioning. The ability to counteract PPARgamma suggests that gammaORF4 plays a role in the pathogenesis of colorectal cancers.
Sabatino
Lina
L
Department of Biological and Environmental Sciences, University of Sannio, Via Port'Arsa 11, 82100 Benevento, Italy.
Casamassimi
Amelia
A
Peluso
Gianfranco
G
Barone
Maria Vittoria
MV
Capaccio
Daniela
D
Migliore
Chiara
C
Bonelli
Patrizia
P
Pedicini
Antonio
A
Febbraro
Antonio
A
Ciccodicola
Alfredo
A
Colantuoni
Vittorio
V
D017398:Alternative Splicing; D000818:Animals; D015153:Blotting, Western; D001973:Bromodeoxyuridine / Q000494:pharmacology; D019556:COS Cells; D018938:Caco-2 Cells; D002467:Cell Nucleus / Q000378:metabolism; D049109:Cell Proliferation; D002839:Chromans / Q000494:pharmacology; D015179:Colorectal Neoplasms / Q000378:metabolism; D018076:DNA, Complementary / Q000378:metabolism; D005091:Exons; D005799:Genes, Dominant; D017930:Genes, Reporter; D005822:Genetic Vectors; D006801:Humans; D066298:In Vitro Techniques; D007438:Introns; D008024:Ligands; D008156:Luciferases / Q000378:metabolism; D051379:Mice; D008856:Microscopy, Fluorescence; D008957:Models, Genetic; D041681:NIH 3T3 Cells; D016366:Open Reading Frames; D047495:PPAR gamma / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D014176:Protein Biosynthesis; D020033:Protein Isoforms; D017434:Protein Structure, Tertiary; D012333:RNA, Messenger / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D045162:Thiazolidinediones / Q000494:pharmacology; D015533:Transcriptional Activation; D014162:Transfection; D000077288:Troglitazone
D002839:Chromans; D018076:DNA, Complementary; D008024:Ligands; D047495:PPAR gamma; D020033:Protein Isoforms; D012333:RNA, Messenger; D045162:Thiazolidinediones; D008156:Luciferases; D001973:Bromodeoxyuridine; D000077288:Troglitazone