BMP-1-induced GBA1 nuclear accumulation provokes CCN2 mRNA expression via importin-β-mediated nucleocytoplasmic pathway

Abstract

Bone morphogenetic protein (BMP)-1 is expressed by odontoblasts in the dentin-pulp complex. Although the functional effects of BMP-1 on the maturation of various preforms of proteins and enzymes involved in initiating mineralization have been widely observed, how BMP-1 affects cellular molecules remains unknown. We performed a comprehensive analysis of BMP-1-altered glycome profiles and subsequent assays to identify the target glycoproteins in human dental pulp cells (hDPCs) by a glycomic approach. In the presence of BMP-1, a lectin microarray analysis and lectin-probed blotting showed that α2,6-sialylation was significantly attenuated in insoluble fractions from hDPCs. Six proteins were identified by a mass spectrometry analysis of α2,6-sialylated glycoproteins purified using a lectin column. Among them, glucosylceramidase (GBA1) was found to accumulate in the nuclei of hDPCs in the presence of BMP-1. Moreover, BMP-1-induced cellular communication network factor (CCN) 2 expression, which is well known as the osteogenesis/chondrogenesis marker, was significantly suppressed in the cells transfected with GBA1 siRNA. Furthermore, importazole, a potent inhibitor of importin-β-mediated nuclear import significantly suppressed BMP-1-induced GBA1 nuclear accumulation and BMP-1-induced CCN2 mRNA expression, respectively. Thus, BMP-1 facilitates the accumulation of GBA1 in the nucleus through the reduction of α2,6-sialic acid, which potentially contributes to the transcriptional regulation of the CCN2 gene via importin-β-mediated nuclear import pathway in hDPCs. Our results offer new insights into the role of the BMP-1-GBA1-CCN2 axis in the development, tissue remodeling, and pathology of dental/craniofacial diseases.