Myosin regulatory light polypeptide 9 (MYL9)

Myosin regulatory light polypeptide 9 (MYL9) is a regulatory light chain subunit of myosin II, primarily expressed in smooth muscle and various nonmuscle cells. It regulates muscle contraction by modulating the ATPase activity of myosin heads, following phosphorylation by myosin light chain kinase and Rho-kinase. MYL9 is essential for the dynamic regulation of cell motility, contraction, cytoskeletal organization, and signal transduction. It interacts with CD69, influencing immune cell recruitment and retention, thus playing a role in inflammation and tumor immunology. MYL9 is implicated in the pathophysiology of diverse diseases, including multiple cancers, cardiovascular conditions, and inflammatory disorders. Differential expression and phosphorylation patterns of MYL9 serve as biomarkers for prognosis and potentially guide therapeutic strategies. Given its central role in smooth muscle physiology, targeted therapies must carefully address possible side effects stemming from impaired contractility in critical organs.

Other names

MYL9Myosin light chain 9Myosin regulatory light chain 2, smooth muscle isoformLC20MLC2MLC-2CMRLC1MYRL2MMIHS4Myosin regulatory light chain 1Myosin RLCEpididymis secretory sperm binding protein

Inhibition of MYL9 phosphorylation reduces smooth muscle contraction and cell motility. Blocking MYL9–CD69 interaction can enhance anti-tumor immune responses by preventing T-cell depletion in the tumor microenvironment. Modulation of upstream kinases (MLCK/ROCK) affects MYL9 activity and downstream cellular functions.