Microphthalmia transcription factor regulates the expression of the novel osteoclast factor GPNMB

Abstract

Microphthalmia transcription factor (MITF) regulates bone homeostasis by inducing expression of critical genes associated with osteoclast function. Gpnmb is a macrophage-enriched gene that has also been shown to be expressed in osteoblasts. Here, we have shown gpnmb to be highly induced in maturing murine osteoclasts. Microarray expression profile analysis identified gpnmb as a potential target of MITF in RAW264.7 cells, subclone C4 (RAW/C4), that overexpress this transcription factor. Electrophoretic mobility shift assays identified a MITF-binding site (M-box) in the gpnmb promoter that is conserved in different mammalian species. Anti-MITF antibody supershifted the DNA-MITF complex for the promoter site while MITF binding was abolished by mutation of this site. The gpnmb promoter was transactivated by co-expression of MITF in reporter gene assays while mutation of the gpnmb M-box prevented MITF transactivation. The induction of gpnmb expression during osteoclastogenesis was shown to exhibit similar kinetics to the known MITF targets, acp5 and clcn7. GPNMB expressed in RAW/C4 cells exhibited distinct subcellular distribution at different stages of osteoclast differentiation. At days 5 and 7, GPNMB protein co-localised with the osteoclast/macrophage lysosomal/endocytic marker MAC-3/LAMP-2, suggesting that GPNMB resides in the endocytic pathway of mature macrophages and is possibly targeted to the plasma membrane of bone-resorbing osteoclasts. The inclusion of gpnmb in the MITF regulon suggests a role for GPNMB in mature osteoclast function.

Lysosomal Stress in Obese Adipose Tissue Macrophages Contributes to MITF-Dependent Gpnmb Induction

“…This causes MITF to shift from the cytosol to nuclei in ATMs, and consequently, Gpnmb induction occurred. Similar MITF-dependent regulation of Gpnmb was recently reported in other cell types like melanoblasts and osteoclasts (42)(43)(44)(45).…”

miRNA-based mechanism for the commitment of multipotent progenitors to a single cellular fate

“…GPNMB expression is controlled by MITF (29). Furthermore, loss of MITF function (30) is reminiscent of the morphological and functional effects of miR-155.…”

Redefinition of the human mast cell transcriptome by deep-CAGE sequencing

“…Genes found here were active not only in monocytes/MCs but also in melanocytes (IDH1, NQO1, and TSPAN4), although melanocytes were not included in the cluster analysis, providing independent validation of the clustering procedure. The osteoclast/melanoblast marker GPNMB, a well-defined MITF-target, 46 was captured by our clustering analysis.…”