Department of Medicine, University of California, San Diego, La Jolla, CA 92093, USA.
Sci Signal. 2010 Dec 21;3(153):ra91. doi: 10.1126/scisignal.2001423.
Mechanical stimulation is crucial for bone growth and remodeling, and fluid shear stress promotes anabolic responses in osteoblasts through multiple second messengers, including nitric oxide (NO). NO triggers production of cyclic guanosine 3',5'-monophosphate (cGMP), which in turn activates protein kinase G (PKG). We found that the NO-cGMP-PKG signaling pathway activates Src in mechanically stimulated osteoblasts to initiate a proliferative response. PKGII was necessary for Src activation, a process that also required the interaction of Src with β₃ integrins and dephosphorylation of Src by a complex containing the phosphatases SHP-1 (Src homology 2 domain-containing tyrosine phosphatase 1) and SHP-2. PKGII directly phosphorylated and stimulated SHP-1 activity, and fluid shear stress triggered the recruitment of PKGII, Src, SHP-1, and SHP-2 to a mechanosome containing β₃ integrins. PKGII-null mice showed defective Src and ERK (extracellular signal-regulated kinase) signaling in osteoblasts and decreased ERK-dependent gene expression in bone. Our findings reveal a convergence of NO-cGMP-PKG and integrin signaling and establish a previously unknown mechanism of Src activation. These results support the use of PKG-activating drugs to mimic the anabolic effects of mechanical stimulation of bone in the treatment of osteoporosis.
机械刺激对于骨骼生长和重塑至关重要，流体切应力通过多种第二信使（包括一氧化氮（NO））促进成骨细胞的合成代谢反应。NO 触发环鸟苷酸 3'，5'-单磷酸（cGMP）的产生，进而激活蛋白激酶 G（PKG）。我们发现，NO-cGMP-PKG 信号通路在机械刺激的成骨细胞中激活Src，从而引发增殖反应。PKGII 对于 Src 的激活是必需的，这一过程还需要 Src 与β₃整合素相互作用以及包含磷酸酶 SHP-1（Src 同源 2 结构域含有酪氨酸磷酸酶 1）和 SHP-2 的复合物对 Src 进行去磷酸化。PKGII 直接磷酸化并刺激 SHP-1 的活性，并且流体切应力触发 PKGII、Src、SHP-1 和 SHP-2 募集到含有β₃整合素的机械体。PKGII 敲除小鼠在成骨细胞中显示出 Src 和 ERK（细胞外信号调节激酶）信号传导的缺陷，以及骨骼中 ERK 依赖性基因表达的减少。我们的发现揭示了 NO-cGMP-PKG 和整合素信号的汇聚，并建立了 Src 激活的先前未知机制。这些结果支持使用 PKG 激活药物来模拟骨骼机械刺激的合成代谢作用，以治疗骨质疏松症。
