Cytokine-specific induction of the TCF-beta inducible early gene (TIEG): Regulation by specific members of the TGF-beta family

Select members of the TGF-beta family of cytokines play key regulatory role s in skeletal development, structure, and turnover. This laboratory has pre viously reported that TGF-beta treatment of immortalized normal human fetal osteoblast (hFOB) cells results in the rapid induction of the mRNA levels of a TGF-beta inducible early gene (TIEG) followed by changes in cell proli feration and bone matrix protein production. Previous studies have also sho wn that nonmembers of the TGF-beta superfamily showed little or no inductio n of TIEG mRNA. This article further addresses the cytokine specificity of this TIEG induction by examining whether activin and select bone morphogene tic proteins, (BMP-2, BMP-4, and BMP-6), which are representative of differ ent subfamilies of this superfamily, also induce the expression of TIEG in hFOB cells. However, TGF-beta remained the most potent of these cytokines, inducing TIEG mRNA steady-state levels at 0.1 ng/ml, with a maximum inducti on of 24-fold at 2.0 ng/ml. The BMP-2 (16-fold), BMP-4 (4-fold), and activi n (1-3-fold) also induced TIEG mRNA levels, but at reduced degrees compared to TGF-beta (24-fold), and only at much higher cytokine concentrations, e. g., 50-100 ng/ml, compared to 2 ng/ml for TGF-beta. BMP-6 showed no effect on TIEG mRNA levels. The TIEG protein levels generally correlated with the mRNA steady-state levels. As with TGF-beta, BMP-2 treatment of hFOB cells w as shown by confocal microscopy to induce a rapid translocation of the TIEG protein to the nucleus. In summary, the relative potencies of these TGF-be ta family members to induce TIEG expression generally follows the general o steoinductive capacity of these cytokines, with TGF-beta much greater than BMP-2 > BMP-4 > activin much greater than BMP-6. (C) 2000 Wiley-Liss, Inc.