Identification of DERMO-1 as a member of helix-loop-helix type transcription factors expressed in osteoblastic cells

Several members of the basic helix-loop-helix (bHLH) type of transcription factors have now been reported, and almost every member of this class has been implicated in transcriptional regulation in cell type determination and differentiation. Previously, we reported that dominant negative HLH proteins are involved in osteoblastic phenotype expression, such as osteocalcin, and hence differentiation (Tamura and Noda [1994] J. Cell Biol. 126:773-782). In this work, we used degenerate PCR cloning in order to identify cDNA clones encoding bHLH proteins expressed in osteoblastic osteosarcoma ROS17/2.8 cells. Sequence analyses of the 47 clones revealed that 11 clones encoded products with a characteristic motif of the bHLH transcription factor family. Of these clones, sequences in the amplified region of seven clones were homologous to the mouse twist, and three clones were homologous to the mouse twist-related HLH protein, Dermo-1. To confirm Dermo-1 mRNA expression in osteoblastic cells, we performed reverse transcription polymerase chain reaction (RT-PCR) analysis using mRNA from ROS17/2.8 cells and MC3T3-E1 cells by Dermo-1 specific primers and Northern blot analysis. These analyses demonstrated that Dermo-1 mRNA was expressed in these osteoblast-like cell lines. Nucleotide sequence analysis of the partial rat Dermo-1 cDNA cloned from ROS17/2.8 library revealed that it has the highest degree of homology with the mouse Dermo-1 cDNA, and the partial amino acid sequence deduced from the obtained rat Dermo-1 was identical with the corresponding region of the mouse Dermo-1 amino acid sequence. To further examine the role of Dermo-1 in the regulation of osteoblastic differentiation, we examined mRNA levels of Dermo-1 and twist in C3H10T1/2 cells treated with recombinant human bone morphogenetic protein (rhBMP)-2. Using the RT-PCR method, the mRNA levels of Dermo-1 and twist were found to be decreased by the treatment with rhBMP-2 in C3H10T1/2 cells. We also observed that the mRNA level of Dermo-1 was decreased about fourfold by the treatment with rhBMP-2 in C3H10T1/2 cells by Northern blot analysis. Moreover, Dermo-1 mRNA was detected at lower levels in 21-day-old differentiated MC3T3-E1 cells compared with 3-day-old undifferentiated MC3T3-E1 cells. These results suggested that Dermo-1 could be involved in the osteoblastic differentiation in a negative manner.