No abstract

This study tests the hypothesis that the activators of peroxisome proliferator-activated receptors (PPARs) and 9-cis-retinoic acid receptor (RXR) regulate human semaphorin 6B (Sema6B) gene expression. The human MCF-7 breast adenocarcinoma cell line was chosen because it expresses Sema6B at a high level. The Sema6B mRNA level was analyzed by RT-PCR and the semaphorin 6B protein content was determined using a polyclonal antibody that we have produced and characterized. Treatments with fenofibrate (a PPAR· activator) and troglitazone (a PPARÁ ligand) strongly decreased the Sema6B mRNA. The drop in Sema6B mRNA level and in protein content was more important when the treatment combined the action of fenofibrate or troglitazone and 9-cis-retinoic acid.On the other hand, no significant change was observed in the Sema6B mRNA and protein levels when the cells were exposed to the combined action of GW610742 (a PPARß activator) and 9-cis-retinoic acid. These data suggest that PPAR·/RXR and PPARÁ/RXR heterodimers are involved in the regulation of Sema6B gene expression and open new perspectives concerning the participation of these nuclear receptors in cell recognition and migration.

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We recently demonstrated that the sphingomyelin (SM) content of adipocyte membranes was negatively correlated with the expression of peroxisome proliferator-activated receptor-Q Q (PPARQ Q) in the subcutaneous adipose tissue of obese women with variable degrees of insulin resistance. We have now investigated whether SM really does have an impact on the expression of PPARQ Q in 3T3-F442A adipocytes. Adding SM to the culture medium for 24 h caused a significant increase in SM content of adipocyte membranes and an acyl chain lengthdependent decrease in the levels of PPARQ Q mRNA and protein.The longer the acyl chain of the fatty acid of SM, the greater was the decrease in PPARQ Q. These data suggest that the nature of the fatty acid is important in the regulation of PPARQ Q by the SM pathway. ß