The Gene for Aromatase, a Rate-Limiting Enzyme for Local Estrogen Biosynthesis, Is a Downstream Target Gene of Runx2 in Skeletal Tissues

Abstract

The essential osteoblast-related transcription factor Runx2 and the female steroid hormone estrogen are known to play pivotal roles in bone homeostasis; however, the functional interaction between Runx2-and estrogenmediated signaling in skeletal tissues is minimally understood. Here we provide evidence that aromatase (CYP19), a rate-limiting enzyme responsible for estrogen biosynthesis in mammals, is transcriptionally regulated by Runx2. Consistent with the presence of multiple Runx2 binding sites, the binding of Runx2 to the aromatase promoter was demonstrated in vitro and confirmed in vivo by chromatin immunoprecipitation assays. The bone-specific aromatase promoter is activated by Runx2, and endogenous aromatase gene expression is upregulated by Runx2 overexpression, establishing the aromatase gene as a target of Runx2. The biological significance of the Runx2 transcriptional control of the aromatase gene is reflected by the enhanced estrogen biosynthesis in response to Runx2 in cultured cells. Reduced in vivo expression of skeletal aromatase gene and low bone mineral density are evident in Runx2 mutant mice. Collectively, these findings uncover a novel link between Runx2-mediated osteoblastogenic processes and the osteoblast-mediated biosynthesis of estrogen as an osteoprotective steroid hormone.

Interrelationship of Runx2 and estrogen pathway in skeletal tissues

“…Interestingly, ERα inhibited Runx2 transactivation function and this inhibition was further enhanced in the presence of 17β-estradiol (49). These results suggest that local production of estrogen by Runx2 through upregulation of aromatase in bone can be regulated by both a positive and negative feedback loop, which can further contribute to the maintenance of bone homeostasis (Fig.…”

“…In contrast, estrogen production was decreased in bone marrow stromal cells derived from Runx2 heterozygous mice. Aromatase expression in the perichondrial and periosteal area was drastically decreased in Runx2 null mice (49). Therefore, aromatase gene expression was well correlated with the level of Runx2 expression in osteoblastic cells.…”

“…Consistent with its role in the physiological control of osteoblastogenesis, Runx2 anabolically modulates bone formation and controls transcriptional signaling pathways that are linked to PTH (16), glucocorticoids (53) and vitamin D3 (54). Runx2 is also a strong positive regulator of aromatase gene expression in osteoblastic cells (49). Runx2 was directly interact with the aromatase gene promoter and stimulated aromatase gene expression in a transient transfection assay.…”

“…Moreover, 1,25-Dihydroxyvitamin D3 enhances the enzyme activity and gene expression of aromatase in the presence of dexamethasone (48). Recently, Runx2 was shown to stimulate aromatase gene expression in skeletal tissues (49). In bone and osteoblast cells, positive regulation of aromatase activity by glucocorticoid, Vitamin D3, and Runx2 may contribute to the local production of estrogens, thus leading to protective effects against osteoporosis especially after menopause.…”

Dysregulation of Notch and ERα signaling in AhR−/−male mice

“…cDNA synthesis and PCR conditions were described (35). Primers for the mouse Cyp19A1 gene were 5′-AAATGCTGAACCCCATGCAG-3′ and 5′-AATCAGGAGAAGGAGGCC-CAT-3′ as used (36). GAPDH, a housekeeping gene, was used as the internal control.…”