Up-regulation of type II collagen gene by 17β-estradiol in articular chondrocytes involves Sp1/3, Sox-9, and estrogen receptor α

The existence of a link between estrogen deprivation and osteoarthritis (OA) in postmenopausal women suggests that 17 beta-estradiol (17 beta-E-2) may be a modulator of cartilage homeostasis. Here, we demonstrate that 17 beta-E-2 stimulates, via its receptor human estrogen receptor alpha 66 (hER alpha 66), type II collagen expression in differentiated and dedifferentiated (reflecting the OA phenotype) articular chondrocytes. Transactivation of type II collagen gene (COL2A1) by ligand-independent transactivation domain (AF-1) of hER alpha 66 was mediated by GC binding sites of the -266/-63-bp promoter, through physical interactions between ER alpha, Sp1/Sp3, Sox9, and p300, as demonstrated in chromatin immunoprecipitation (ChIP) and Re-Chromatin Immuno-Precipitation (Re-ChIP) assays in primary and dedifferentiated cells. 17 beta-E-2 and hER alpha 66 increased the DNA-binding activities of Sp1/Sp3 and Sox-9 to both COL2A1 promoter and enhancer regions. Besides, Sp1, Sp3, and Sox-9 small interfering RNAs (siRNAs) prevented hER alpha 66-induced transactivation of COL2A1, suggesting that these factors and their respective cis-regions are required for hER alpha 66-mediated COL2A1 up-regulation. Our results highlight the genomic pathway by which 17 beta-E-2 and hER alpha 66 modulate Sp1/Sp3 heteromer binding activity and simultaneously participate in the recruitment of the essential factors Sox-9 and p300 involved respectively in the chondrocyte-differentiated status and COL2A1 transcriptional activation. These novel findings could therefore be attractive for tissue engineering of cartilage in OA, by the fact that 17 beta-E-2 could promote chondrocyte redifferentiation.