title: The truncated splice variant of peroxisome proliferator-activated receptor alpha, PPARα-tr, autonomously regulates proliferative and pro-inflammatory genes.
abstract: BACKGROUND
  The peroxisome proliferator-activated receptor alpha (PPARα) controls lipid/energy homeostasis and inflammatory responses. The truncated splice variant PPARα-tr was suggested to exert a dominant negative function despite being unable to bind consensus PPARα DNA response elements.
  
  
  METHODS
  The distribution and variability factor of each PPARα variant were assessed in the well-characterized cohort of human liver samples (N = 150) on the mRNA and protein levels. Specific siRNA-mediated downregulation of each transcript as well as specific overexpression with subsequent qRT-PCR analysis of downstream genes was used for investigation of specific functional roles of PPARα-wt and PPARα-tr forms in primary human hepatocytes.
  
  
  RESULTS
  Bioinformatic analyses of genome-wide liver expression profiling data suggested a possible role of PPARα-tr in downregulating proliferative and pro-inflammatory genes. Specific gene silencing of both forms in primary human hepatocytes showed that induction of metabolic PPARα-target genes by agonist WY14,643 was prevented by PPARα-wt knock-down but neither prevented nor augmented by PPARα-tr knock-down. WY14,643 treatment did not induce proliferative genes including MYC, CDK1, and PCNA, and knock-down of PPARα-wt had no effect, while PPARα-tr knock-down caused up to 3-fold induction of these genes. Similarly, induction of pro-inflammatory genes IL1B, PTGS2, and CCL2 by IL-6 was augmented by knock-down of PPARα-tr but not of PPARα-wt. In contrast to human proliferative genes, orthologous mouse genes were readily inducible by WY14,643 in PPARα-tr non-expressing AML12 mouse hepatocytes. Induction was augmented by overexpression of PPARα-wt and attenuated by overexpression of PPARα-tr. Pro-inflammatory genes including IL-1β, CCL2 and TNFα were induced by WY14,643 in mouse and human cells and both PPARα forms attenuated induction. As potential mechanism of PPARα-tr inhibitory action we suggest crosstalk with WNT/β-catenin pathway. Finally, treatment with WY14,643 in the presence of PPARα-tr resulted in the significant reduction of cell viability of AML12 and human ovarian cancer cell line, SKOV3.
  
  
  CONCLUSIONS
  Our data suggest that the truncated PPARα splice variant functions as an endogenous inhibitor of proliferative and pro-inflammatory genes in human cells and that its absence in mouse may explain species-specific differences in fibrate-induced hepatocarcinogenesis.
authors.affiliation: Dr. Margarete Fischer-Bosch Institute of Clinical Pharmacology, Auerbachstr. 112, 70736, Stuttgart, and University of Tuebingen, Tuebingen, Germany. maria.thomas@ikp-stuttgart.de.
authors.forename: Maria
authors.initials: M
authors.lastname: Thomas
authors.affiliation: Dr. Margarete Fischer-Bosch Institute of Clinical Pharmacology, Auerbachstr. 112, 70736, Stuttgart, and University of Tuebingen, Tuebingen, Germany. christine.bayha@ikp-stuttgart.de.
authors.forename: Christine
authors.initials: C
authors.lastname: Bayha
authors.affiliation: Dr. Margarete Fischer-Bosch Institute of Clinical Pharmacology, Auerbachstr. 112, 70736, Stuttgart, and University of Tuebingen, Tuebingen, Germany. kathrin.klein@ikp-stuttgart.de.
authors.forename: Kathrin
authors.initials: K
authors.lastname: Klein
authors.affiliation: Dr. Margarete Fischer-Bosch Institute of Clinical Pharmacology, Auerbachstr. 112, 70736, Stuttgart, and University of Tuebingen, Tuebingen, Germany. info@muon-stat.com.|Present address: MUON-STAT, Klugestraße 28, 70197, Stuttgart, Germany. info@muon-stat.com.
authors.forename: Simon
authors.initials: S
authors.lastname: Müller
authors.affiliation: University Children Hospital (KUNO), Regensburg University Hospital, Regensburg, Germany. thomas.weiss@klinik.uni-regensburg.de.
authors.forename: Thomas S
authors.initials: TS
authors.lastname: Weiss
authors.affiliation: Dr. Margarete Fischer-Bosch Institute of Clinical Pharmacology, Auerbachstr. 112, 70736, Stuttgart, and University of Tuebingen, Tuebingen, Germany. Matthias.schwab@ikp-stuttgart.de.|Department of Clinical Pharmacology, University of Tuebingen, Tuebingen, Germany. Matthias.schwab@ikp-stuttgart.de.
authors.forename: Matthias
authors.initials: M
authors.lastname: Schwab
authors.affiliation: Dr. Margarete Fischer-Bosch Institute of Clinical Pharmacology, Auerbachstr. 112, 70736, Stuttgart, and University of Tuebingen, Tuebingen, Germany. uli.zanger@ikp-stuttgart.de.
authors.forename: Ulrich M
authors.initials: UM
authors.lastname: Zanger
mesh_terms: D017398:Alternative Splicing / Q000235:genetics; D000818:Animals; D063646:Carcinogenesis / Q000235:genetics*; D006528:Carcinoma, Hepatocellular / Q000235:genetics* / Q000473:pathology; D045744:Cell Line, Tumor; D049109:Cell Proliferation / Q000235:genetics; D015972:Gene Expression Regulation, Neoplastic; D006801:Humans; D008113:Liver Neoplasms / Q000235:genetics* / Q000473:pathology; D051379:Mice; D047493:PPAR alpha / Q000235:genetics* / Q000378:metabolism
chemical_list: D047493:PPAR alpha