Modulation of gene expression in human osteoblasts by targeting a distal promoter region of human estrogen receptor-α gene

Abstract

Estrogen receptor (ER) α is expressed during osteoblast differentiation; however, both its functional role in bone metabolism and its involvement in osteoporotic pathogenesis caused by estrogen deficiency are not well understood. Loss of ERα gene expression could be one of the mechanisms leading to osteoporosis. Therefore, we investigated a possible modulation of ERα gene expression in a human osteoblastic cell line and in four primary osteoblast cultures by using a decoy strategy. Double stranded DNA molecules, mimicking a regulatory region of the ERα gene promoter (DNA-102) and acting as a 'silencer' in breast cancer cells, were introduced into osteoblasts as 'decoy' cis-elements to bind and functionally inactivate a putative negative transcription factor, and thus to induce ERα gene expression. We found that the DNA-102 molecule was able to specifically bind osteoblast nuclear proteins. Before decoy treatment, absence or variable low levels of ERα RNAs in the different cultures were detected. When the cells were transfected with the DNA-102 decoy, an increase in expression of ERα and osteoblastic markers, such as osteopontin, was observed, indicating a more differentiated osteoblastic phenotype both in the cell line and in primary cultures. These results showed that the DNA-102 sequence competes with endogenous specific negative transcription factors that may be critical for a decrease in or lack of ERα gene transcription. Therefore, osteoblastic transfection with the DNA-102 decoy molecule may be considered a tempting model in a putative therapeutic approach for those pathologies, such as osteoporosis, in which the decrease or loss of ERα expression plays a critical role in bone function.