NONO is essential in maintaining airway smooth muscle contractility through PDE4/cAMP signaling pathways

Non-POU domain containing octamer binding protein (NONO) is a multifunctional nuclear protein which plays important roles in regulating nuclear processes such as transcription and splicing. However, the role of NONO played in regulating airway smooth muscle (ASM) contraction remains largely unknown. In this study, we aimed to delineate the effects and the underlying mechanisms of NONO on ASM contraction. By deploying NONO gene knockout (NONO K.O.) mice, we examined tracheal contractility using a mechanical recording system. The expression of PDE4 was quantified by real-time PCR, the contents of IP₃, calmodulin, cAMP, myosin light chain kinase (MLCK) and phosphorylated MLC (p-MLC) were determined through ELISA. The results showed a significant decline of ASM contractility in NONO K.O. mice compared with wild type (W.T.), PDE inhibitor IBMX and PDE4 inhibitor rolipram largely attenuated the decreased ASM contraction of NONO K.O. mice. PDE4A-C mRNA expression were up-regulated while basal level of cAMP, calmodulin and IP₃ declined in NONO K.O. mice. Furthermore, two important components of the contractile apparatus, MLCK and p-MLC, were also decreased after carbachol (CCh) stimulation. These data demonstrated that NONO was capable of regulating ASM contraction through, at least partially, PDE4/cAMP signaling pathways and provided a novel regulatory target of ASM contractility.