Type II cGMP-dependent protein kinase mediates osteoblast mechanotransduction.
Continuous bone remodeling in response to mechanical loading is critical for skeletal integrity, and interstitial fluid flow is an important stimulus for osteoblast/osteocyte growth and differentiation. However, the biochemical signals mediating osteoblast anabolic responses to mechanical stimulation are incompletely understood. In primary human osteoblasts and murine MC3T3-E1 cells, we found that fluid shear stress induced rapid expression of c-fos, fra-1, fra-2, and fosB/DeltafosB mRNAs; these genes encode transcriptional regulators that maintain skeletal integrity. Fluid shear stress increased osteoblast nitric oxide (NO) synthesis, leading to activation of cGMP-dependent protein kinase (PKG). Pharmacological inhibition of the NO/cGMP/PKG signaling pathway blocked shear-induced expression of all four fos family genes. Induction of these genes required signaling through MEK/Erk, and Erk activation was NO/cGMP/PKG-dependent. Treating cells with a membrane-permeable cGMP analog partly mimicked the effects of fluid shear stress on Erk activity and fos family gene expression. In cells transfected with small interfering RNAs (siRNA) specific for membrane-bound PKG II, shear- and cGMP-induced Erk activation and fos family gene expression was nearly abolished and could be restored by transducing cells with a virus encoding an siRNA-resistant form of PKG II; in contrast, siRNA-mediated repression of the more abundant cytosolic PKG I isoform was without effect. Thus, we report a novel function for PKG II in osteoblast mechanotransduction, and we propose a model whereby NO/cGMP/PKG II-mediated Erk activation and induction of c-fos, fra-1, fra-2, and fosB/DeltafosB play a key role in the osteoblast anabolic response to mechanical stimulation.
Rangaswami
Hema
H
Department of Medicine and Cancer Center, University of California, San Diego, La Jolla, California 92093, USA.
Marathe
Nisha
N
Zhuang
Shunhui
S
Chen
Yongchang
Y
Yeh
Jiunn-Chern
JC
Frangos
John A
JA
Boss
Gerry R
GR
Pilz
Renate B
RB
D000818:Animals; D002118:Calcium / Q000378:metabolism; D015815:Cell Adhesion Molecules / Q000378:metabolism; D002460:Cell Line; D006152:Cyclic GMP / Q000096:biosynthesis / Q000494:pharmacology; D017869:Cyclic GMP-Dependent Protein Kinases / Q000378:metabolism*; D004789:Enzyme Activation / Q000187:drug effects; D048049:Extracellular Signal-Regulated MAP Kinases / Q000378:metabolism; D005786:Gene Expression Regulation / Q000187:drug effects; D006801:Humans; D040542:Mechanotransduction, Cellular / Q000187:drug effects; D051379:Mice; D008840:Microfilament Proteins / Q000378:metabolism; D019950:Mitogen-Activated Protein Kinase 1 / Q000378:metabolism; D018716:Molecular Mimicry / Q000187:drug effects; D009569:Nitric Oxide / Q000096:biosynthesis; D052250:Nitric Oxide Synthase Type III / Q000378:metabolism; D010006:Osteoblasts / Q000166:cytology* / Q000187:drug effects / Q000201:enzymology*; D010750:Phosphoproteins / Q000378:metabolism; D010766:Phosphorylation / Q000187:drug effects; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D012212:Rheology; D015398:Signal Transduction / Q000187:drug effects; D013314:Stress, Mechanical; D000098662:Vasodilator-Stimulated Phosphoprotein
D015815:Cell Adhesion Molecules; D008840:Microfilament Proteins; D010750:Phosphoproteins; D012333:RNA, Messenger; D000098662:Vasodilator-Stimulated Phosphoprotein; D009569:Nitric Oxide; D052250:Nitric Oxide Synthase Type III; D017869:Cyclic GMP-Dependent Protein Kinases; D048049:Extracellular Signal-Regulated MAP Kinases; D019950:Mitogen-Activated Protein Kinase 1; D006152:Cyclic GMP; D002118:Calcium