Differences in the Formation of PPARα-RXR/acoPPRE Complexes between Responsive and Nonresponsive Species upon Fibrate Administration
- 1Unidad de Farmacologı́a y Farmacognosia (C.R., A.C., J.C.L.), and 2Unidad de Bioquı́mica y Biologı́a Molecular (V.N., C.J.C.), Facultad de Farmacia, Universidad de Barcelona, Barcelona, Spain
Abstract
Peroxisome proliferator-activated receptor-α (PPARα) is responsible for the hypolipidemic, peroxisome proliferation and carcinogenic effects of fibrates. Rats and mice are responsive, but guinea pigs and primates are resistant to the proliferative and carcinogenic effects of these drugs, but the hypolipidemic effect is still manifest. It is not yet clear whether humans should be considered unresponsive, and there is concern about the long-term safety of fibrates. We present molecular evidence for the reported resistance of human cells to peroxisome proliferation by describing a deficient interaction of nuclear extracts from human cells with an acyl-CoA oxidase (ACO)-peroxisome proliferator response element probe upon fibrate addition. Electrophoretic mobility shift assay analysis showed that ciprofibrate elicited a concentration-dependent increase in the binding of nuclear extracts from cells of rat (Morris) and human (HepG2) origin to an ACO-peroxisome proliferator response element probe, although in HepG2 cells the increase was of marginal statistical significance. In Morris cells, the increase was more marked than in HepG2 cells (4-fold versus 1.5-fold at 0.2 mM ciprofibrate), and maximal binding was achieved earlier in Morris (30 min) than in HepG2 cells (3 h). Morris cells responded to the addition of ciprofibrate by increasing the levels of ACO mRNA, whereas HepG2 did not. The ratio between PPARβ/PPARα mRNAs was higher in HepG2 cells than in Morris cells (3.2 versus 1.9), pointing to an antagonizing effect of PPARβ on PPARα activity. These results were obtained in untransfected cells expressing their own basal set of receptors. We also provide evidence of the translocation of PPARα from the cytosol to the nucleus upon activation by ciprofibrate.
Footnotes
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Dr. Juan C. Laguna, Unidad de Farmacologı́a y Farmacognosia, Facultad de Farmacia, Universidad de Barcelona, Núcleo Universitario de Pedralbes, Barcelona E-08028, Spain. E-mail: laguna{at}farmacia.far.ub.es
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This study was partly funded by grants from the FundacióPrivada Catalana de Nutrició i Lípids, Comision Interministerial de Ciencia y Tecnologia (SAF97-0215 to J.C.L. and SAF96-74 to C.J.C.), and from the “Generalitat de Catalunya,” SGR96-84 and SGR98-33. C.R. was a recipient of a fellowship from the Generalitat de Catalunya, and A.C. was a recipient of a fellowship from the Ministerio de Educacion y Cultura.
- Abbreviations:
- PPAR
- peroxisome proliferator-activated receptor
- PPRE
- peroxisome proliferator response element
- RXR
- 9-cis retinoic acid receptor
- DMSO
- dimethyl sulfoxide
- GAPDH
- glyceraldehyde-3-phosphate dehydrogenase
- RT-PCR
- reverse transcription-polymerase chain reaction
- ACO
- acyl-CoA oxidase
- HB
- hypotonic buffer
- EMSA
- electrophoretic mobility shift assay
- APRT
- adenosyl phosphoribosyl transferase
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- Received August 23, 1999.
- Accepted March 24, 2000.
- The American Society for Pharmacology and Experimental Therapeutics
