Figure 7. Signaling Defect in PKG II-null Osteoblasts.
A. Semi-quantitative RT-PCR for PKG I and II expression in primary calvarial osteoblasts isolated from one week-old PKG II−/− mice and their wild-type litter mates (representative of two experiments).
B. and C. Wild-type and PKG II-null primary osteoblasts were stimulated with either fluid shear stress (FSS; 12 dynes/cm2) or 100 μM 8-CPT-cGMP (cGMP) for 5 min, and Src and Erk activation were analyzed as in Fig. 1E [representative of two (B) or three (C) experiments].
D. Tibial diaphyses were isolated from one week-old PKG II−/− mice and their wild-type litter mates, and c-fos, fra-2, and gapd mRNA amounts were measured by quantitative RT-PCR (mean ± SEM; n=3; * p < 0.05 for wild-type versus knockout mice).
E. Model of Src and Erk activation by fluid shear stress via NO/cGMP/PKG II, depicting the assembly of a mechano-sensitive complex containing PKG II, Shp-1/2, and Src bound to the cytoplasmic tail of β3, as described in the text (x = docking protein). Activation of the Ras/Raf/MEK/Erk cascade by Src occurs via Shc-dependent and -independent pathways (33).