MYL9

Official Full Name

myosin light chain 9

Organism

Homo sapiens

GeneID

10398

Background

Myosin, a structural component of muscle, consists of two heavy chains and four light chains. The protein encoded by this gene is a myosin light chain that may regulate muscle contraction by modulating the ATPase activity of myosin heads. The encoded protein binds calcium and is activated by myosin light chain kinase. Two transcript variants encoding different isoforms have been found for this gene. [provided by RefSeq, Jul 2008]

Synonyms

LC20; MLC2; MRLC1; MYRL2; MLC-2C; MMIHS4;

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Detailed Information

The MYL9 gene is located on human chromosome 20q11.23 and contains 8621 bases, 8 introns, and 17 exons. Its encoded 20KD myoglobin regulatory light chain is an important component of myosin. The latter structure consists of two heavy chains and four light chains. As a superfamily protein, it is an important component of muscle cells and some non-muscle cytoskeleton. Various regulatory factors are involved in almost all cellular physiology and pathological processes by regulating their light chain phosphorylation and dephosphorylation, especially in the proliferation, invasion and migration of tumor cells.

Figure 1. Contraction of smooth muscle cell: cellular pathway and the role of MYL9 and of other genes related to MMIHS. (Moreno, C. A., et al. 2018)

Cellular Pathway Involved in MYL9 Gene

Studies have found that the MYL9 gene is involved in up to 28 cell pathways, such as the Rho/ROCK/MYL9 signal transduction pathway, the PKA signal transduction pathway, the PAK signal transduction pathway, the ZIP signal transduction pathway, and the PKC cell pathway. It is a molecular motor of the cytoskeleton through the regulation of various cellular pathways, which are widely involved in biological processes such as endocytosis, organelle movement, cell migration, substance transport, cytoplasmic flow, mitosis, extracellular secretion and signal transduction.

Rho, a member of the Ras superfamily, is an upstream activator of Rho kinase. It is a small molecule guanylate binding protein. Because of its GTPase activity, it is also known as RhoGTPase (such as RhoA, Rac1 and Cdc42). As a substrate for ROCK activation, myosin phosphatase accepts activation signals from Rho and Rho kinases to phosphorylate regulatory subunits, ultimately leading to inactivation of themselves, and inactive myosin phosphatase cannot light myosin Dephosphorylation of the chain MYL9 increases the level of phosphorylation of MYL9 in the cytoplasm and promotes actin and myosin interactions. It has also been reported that ROCK can promote the increase of intracellular Ca2+ concentration and activate MYL9 phosphorylation under the action of MLCK by activating Ca2+/calmodulin-dependent MLCK.

MYL9 and Tumor

The migration of cancer cells requires Rho-GTPases and its signal transduction-related components, while ROCK and MYL9 can play a key role. The activated ROCK specifically phosphorylates the myosin light chain (MYL9) site Ser19. Therefore, this particular ROCK-phosphorylation has been widely used as an indicator of ROCK activity. Phosphorylation at the Ser19 site of MYL9 is important for the contraction and migration of myosin. In the study of the negative regulation of the proto-oncogene DEK on non-small cell lung cancer, it was found that with the depletion of the proto-oncogene DEK, the RhoARNA and protein levels in the cells were significantly reduced, while the RhoA-GTP activity level and the phosphorylation of the downstream effector MYL9 also decreased. Thus, DEK-mediated cell motility is through the Rho/ROCK/MYL9 signal transduction pathway, which promotes cytoskeletal dynamics and cellular movement.

MYL9 enhances phosphorylation of MYL9 through a variety of regulatory mechanisms, resulting in enhanced metastasis and invasion of breast cancer cells. It has also been found in the study that the reduction in DEK can directly negatively regulate the Rho/ROCK/MYL9 pathway. It is also confirmed during the metastasis of breast cancer that srGAP3 plays a role in mediating breast cancer cell metastasis through Rho/ROCK/MYL9. Ovarian cancer is highly invasive. Fasudil is a specific inhibitor of ROCK, and Fasudil inhibits phosphorylation of MYL9 via the Rho/ROCK pathway, resulting in decreased phosphorylation of MYL9 and recombination of cytoskeleton in the cell, which in turn inhibits cell movement and weakens the invasiveness of ovarian cancer.

References:

Moreno, C. A. , Sobreira, N. , Pugh, E. , Zhang, P. , Steel, G. , & Torres, Fábio Rossi, et al. (2018). Homozygous deletion in myl9 expands the molecular basis of megacystis–microcolon–intestinal hypoperistalsis syndrome. European Journal of Human Genetics.
Wang, J. H. , Zhang, L. , Huang, S. T. , Xu, J. , Zhou, Y. , & Yu, X. J. , et al. (2013). Expression and prognostic significance of myl9 in esophageal squamous cell carcinoma. Journal of Third Military Medical University, 12(4), e0175280.
Tan, X. , & Chen, M. . (2014). Mylkandmyl9expression in non-small cell lung cancer identified by bioinformatics analysis of public expression data. Tumor Biology, 35(12), 12189-12200.

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