title: Mutual regulation of hypoxic and retinoic acid related signalling in tubular proximal cells.
abstract: Hypoxia-inducible factor-1α (HIF-1α) and all-trans retinoic acid (ATRA) afford protection in several experimental models of kidney disease. HIF-1α protein is degraded under normoxia but stabilized by hypoxia, which activates its transcription factor function. ATRA activates another set of transcription factors, the retinoic acid receptors (RAR) α, β and γ, which mediate its effects on target genes. ATRA also up-regulates the expression of RAR α, β and γ at the transcriptional level. Here we demonstrate the presence of mutual regulation of hypoxic and retinoic acid related signalling in tubular proximal cells. In human proximal tubular HK-2 cells we have found that: (i) ATRA treatment induces HIF-1α under normoxic conditions and also synergizes with hypoxia leading to the over-expression of HIF-1α and vascular endothelial growth factor-A, a HIF-1α-regulated renal protector. ATRA-induced HIF-1α expression involved stabilization of HIF-1α mRNA but not of HIF-1α protein. (ii) Expression of HIF-1α is an absolute requirement for the transcriptional up-regulation of RARβ by ATRA. Transfection with HIF-1α siRNA abolished the induction by ATRA of the expression of both RARβ mRNA and protein while treatment with HIF-1α inhibitor YC-1 results in the abolishment of ATRA-induced activity of a retinoic acid-response element (RARE) construct from the RARβ promoter. (iii) Hypoxia up-regulates RARβ through HIF-1α since this effect was inhibited by HIF-1α knockdown. In contrast to ATRA-induced RARβ up-regulation, induction of RARβ expression by ATRA did not involve transcriptional up-regulation as hypoxia did not increase the expression of RARβ mRNA or the activity of the RARE construct. These results suggest the presence of crosstalk between hypoxia/HIF-1α and ATRA/RARβ that may be physiologically and pharmacologically relevant.
authors.affiliation: Departamento de Fisiología, Universidad de Alcalá, Alcalá de Henares, Madrid, Spain. anab.fernandez@uah.es
authors.forename: Ana Belén
authors.initials: AB
authors.lastname: Fernández-Martínez
authors.forename: María Isabel Arenas
authors.initials: MI
authors.lastname: Jiménez
authors.forename: Irene Sánchez
authors.initials: IS
authors.lastname: Hernández
authors.forename: María Laura
authors.initials: ML
authors.lastname: García-Bermejo
authors.forename: Victoria Moreno
authors.initials: VM
authors.lastname: Manzano
authors.forename: Elia Aguado
authors.initials: EA
authors.lastname: Fraile
authors.forename: Francisco Javier
authors.initials: FJ
authors.lastname: de Lucio-Cazaña
mesh_terms: D015687:Cell Hypoxia / Q000235:genetics / Q000502:physiology; D002460:Cell Line; D005786:Gene Expression Regulation; D006801:Humans; D051795:Hypoxia-Inducible Factor 1, alpha Subunit / Q000235:genetics / Q000378:metabolism*; D018168:Receptors, Retinoic Acid / Q000235:genetics / Q000378:metabolism; D015398:Signal Transduction; D015533:Transcriptional Activation; D014162:Transfection; D014212:Tretinoin / Q000378:metabolism* / Q000494:pharmacology; D015854:Up-Regulation; D042461:Vascular Endothelial Growth Factor A / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism*
chemical_list: D051795:Hypoxia-Inducible Factor 1, alpha Subunit; D018168:Receptors, Retinoic Acid; D042461:Vascular Endothelial Growth Factor A; C082925:retinoic acid receptor beta; D014212:Tretinoin