DYNAMIC SUBCELLUAR DISTRIBUTION OF FKBP51 DURING ADIPOCYTE DIFFERENTIATION IS RELATED TO PKA SIGNALLING

SUSPERREGUY S; GUBER, S; GALIGNIANA, MD; GRACIELA PIWIEN-PILIPUK

Edimburgo, Escocia

Congreso; 14th International Congress on Hormonal Steroids and Hormones & Cancer; 2010

Obesity is the resultant of both increased adipocyte size and development of new fat cells. Glucocorticoids play an important role in adipogenesis via the glucocorticoid receptor (GR), which exists as an oligomer bound to hsp90 and high MW immunophilins (IMMs). Here, we studied the role of IMMs in adipogenesis. When 3T3-L1 preadipocytes were induced to differentiate with a cocktail containing dexamethasone, IBMX and insulin, Western blot analysis showed that FKBP51 protein level progressively increased whereas FKBP52 faded. Hsp90, hsp70 and Cyp40 remained unchanged. In preadipocytes 3T3-L1 FKBP51 localizes mainly in mitochondria, as assessed by indirect immunofluorescence and subcellular fractionation. Interestingly, FKBP51 translocated to the nucleus co-localizing with GR when adipogenesis is induced. FKBP51 nuclear localization was transient, such that 48 h after the induction of differentiation it cycled back to mitochondria. Moreover, co-immunoprecipitation assays showed that GR is complexed with more FKBP51 than FKBP52. Reporter gene assays showed that FKBP51 reduced GR transcriptional capacity, suggesting that nuclear FKBP51 controls GR target genes during the differentiation. IBMX alone promoted an efficient nuclear relocalization of FKBP51. Since increased cAMP leads to PKA activation, we assayed the effect of PKA inhibitors and found that FKBP51 relocalization was abrogated. PKA signaling is required for 3T3-L1 cells to differentiate in adipocytes, CREB being a well known PKA target. When adipogenesis was induced, phospho-CREB co-localized with nuclear FKBP51. Immunoprecipitation assays showed that FKBP51 interacts with CREB. Importantly, overexpression of FKP51 decreased CREB-dependent c-fos promoter activity. In summary, FKBP51 shows dynamic changes of expression and concentrates in the nucleus during the onset of adipocyte differentiation in response to PKA signaling cascade. This transient nuclear concentration of the IMM may play a key role in the control of the expression of genes required for the acquisition of adipocyte phenotype.