Figure 8. The ABL-TAZ amplification loop required for osteoblastogenesis is regulated by the adapter protein 3BP2.

(A) Primary murine osteoblasts from WT or Sh3bp2^–/– (KO) mice were cultured in osteogenic medium. Nuclear lysates were probed with the indicated antibodies for Western blot analysis. (B) Primary murine osteoblasts from WT or Sh3bp2^–/– (KO) mice were infected with an empty vector control or FKBP-ABL–expressing retroviral vector (WT) and cultured in osteogenic medium. Nuclear lysates were probed with the indicated antibodies for Western blot analysis. (C) Osteoblasts in B were cultured in osteogenic medium and stained with alizarin red S solution. n = 3. (D) NIH3T3 cells infected with an empty vector control or a retroviral vector expressing FKBP-ABL (WT or KD) were cultured in adipogenic medium and stained with oil red O solution. Upper panel: bright-field images; bottom panel: oil red O–stained images; original magnification ×200. n = 3. (E) Culture plate images of the oil red O staining in D. n = 3. (F) qPCR analysis of aP2 mRNA expression in cells in D and E cultured for 3 to 6 days. n = 3. Data are presented as the mean ± SEM. (G) Luciferase activity from an aP2 reporter assay in HEK293T cells cotransfected with the indicated constructs. n = 3. *P < 0.05, by ANOVA with a Tukey-Kramer post-hoc test. (H) Schematic model of reciprocal protein stabilization of ABL and TAZ , which regulates osteoblastogenesis through the activation of RUNX2.