Identification of FAZF as a novel BMP2-induced transcription factor during osteoblastic differentiation

Bone morphogenetic protein 2 (BMP2) is a key factor in the regulation of osteoblastic differentiation; however, its downstream mediators are not fully understood. Previously, we identified and characterized transcription factor promyelocytic leukemia zinc finger protein (PLZF), composed of an N-terminal BTB/POZ and C-terminal zinc finger motifs, as an upstream factor of CBFA1 (Runx2/core-binding factor 1). PLZF was induced in an osteoblastic differentiation medium, but was not induced by BMP2. Here, we report the identification of transcription factor fanconi anemia zinc finger protein (FAZF), which is closely related to PLZF. FAZF was induced by BMP2 in human mesenchymal stem cells (hMSCs). In addition to the full-length FAZF, we also identified alternatively spliced mRNAs in which the C-terminal zinc finger motifs were deleted (designated BTB/POZ-only FAZF). Both the full-length and BTB/POZ-only FAZF mRNAs were equally expressed in BMP2-treated hMSCs. The full-length FAZF was exclusively detected in the nucleus, whereas the BTB/POZ-only FAZF protein was localized in the cytoplasm of the transfected cells. The full-length FAZF, but not the BTB/POZ-only FAZF, increased the expression of osteoblastic differentiation markers, including CBFA1, collagen 1A1, osteocalcin, and alkaline phosphatase in C2C12 cells. In conclusion, both FAZF and PLZF differentially participate in the regulation of osteoblastic differentiation via the BMP2 and CBFA1 signaling pathways, respectively.