The Cellular Senescence-Inhibited Gene Is Essential for PPM1A Myristoylation To Modulate Transforming Growth Factor beta Signaling

The cellular senescence-inhibited gene (CSIG) is implicated in important biological processes, including cellular senescence and apoptosis. Our work showed that CSIG is involved in the myristoylation of the serine/threonine protein phosphatase PPM1A. Previous research has shown that myristoylation is necessary for PPM1A to dephosphorylate Smad2 and Smad3. However, the control and the biological significance of the myristoylation remain poorly understood. In this study, we found that CSIG knockdown disturbs PPM1A myristoylation and reduces the dephosphorylation by PPM1A of its substrate Smad2. By regulating PPM1A myristoylation, CSIG is involved in modulating the signaling of transforming growth factor beta (TGF-beta). Further study of the mechanism indicated that CSIG facilitates the interaction between N-myristoyltransferase 1 (NMT1) and PPM1A. Taking the data together, we found that CSIG is a regulator of PPM1A myristoylation and TGF-beta signaling. By promoting the myristoylation of PPM1A, CSIG enhanced the phosphatase activity of PPM1A and further inhibited TGF-beta signaling. This work not only extends the biological significance of CSIG but also provides new ideas and a reference for the study of the regulatory mechanism of myristoylation.