Education

Tokyo Institute of Technology, Japan
B.S. Chemistry, 03/77
Tokyo Institute of Technology, Japan
M.S. Biochemistry, 03/77
Osaka University, Japan
PhD. Biochemistry, 03/82

Research Interests and Accomplishment:

1. Regulation of smooth muscle and non-muscle myosin II
In early my career I found that myosin light chain phopshorylation is required for the activation of actin-activated ATPase activity of smooth muslce myosin. I am one of the reserchers who independently found that myosin light chain phosphorylation activates actomyosin ATPase activity and smooth muscle contraction. We found that the phosphorylation dependent conformational transition of myosin molecule is critical for both the activation of the ATPase activity and the formation of myosin filaments. We also found that myosin regulatory light chain (RLC) can be phopshorylated multiple sites by different protein kinases. It was originally though that RLC is phosphorylated at a single site (Ser19) by myosin light chain kinase (MLCK), but we found that RLC can be phopshorylated at additional site (Thr18), which stabilizes the formation of myosin filaments. Subsequently, it was found that the phosphorylation of this sites are achieved by other protein kinases, and it is now thought that the phosphorylation at Ser19 and Thr18 plays a critical role in myosin II function in cell migration and contraction. We also found that protein kinase C phosphorylates RLC at Ser1 and Ser2, which facilitates disassembly of myosin filaments to induce cytoskeletal reorganization during cell migration such as cancer cell migration and invasion.
2. Regulation of myosin phosphorylation in smooth muscle contraction and non-muscle cell migration such as cancer cells.
It is now known that there is a Ca2+ independent mechanism for the regulation of RLC phosphorylation in addition to Ca2+ dependent mechanism, in which myosin light chain phosphatase (MLCP) plays a key role. We found that agonist induced phosphorylation of MYPT1, a regulatory subunit of MLCP, and CPI-17, a MLCP specific inhibitor, down-regulate MLCP, thus increaseing RLC phosphorylation. The responsible protein kinase is a Rho kinase, a major down-stream kinase of RhoA pathway. We also found that cGMP kinase phopshorylates the sites right next to the inhibitory sites catalyzed by Rho kinase, and cGMP kinase dependent phopshorylation cancells the effect of Rho kinase dependent phosphorylation. This contributes to the cGMP induced relaxation of smooth muscle. Quite recently, we found that Rac1 contributes to the regulation of myosin phosphorylation. Our finding suggests that RhoA and Rac1 concertedly regulate myosin light chain phosphorylation, thus controlling myosin phosphorylation. It is expected that this mechanism is operating in cancer cell migration and invasion. In cell migration, we found that ZIP kinase phosphorylates both Ser19 and Thr18, and this kinase plays a significant role in the phosphorylation of myosin II in migrating cells, thus the control of actin dynamics in non-muscle cell migration such as cancer cell migration. Recently, we set-up 3D cell migration assay system.
3. Function and regulation of unconventional myosin and its function in actin cytoskeletal rearrangement
I have been studying on the function and regulation of unconventional myosin at the molecular and cellular level. For myosin V, we demonstrated that the tail-domain interacts with the motor domain, which results in the inhibition of the motor activity and created the 3D model for the regulation of myosin Va. Moreover, we found that a specific cargo molecule of myosin Va, melanophilin, activates the motor activity due to the disruption of the head-tail interaction. For myosin VIIa, we first demonstrated the motor activity with a plus directionality on actin, and showed that myosin VIIa is a high duty ratio processive motor. We also found that this myosin is a monomeric myosin and can form a dimer with its cargo complex and that myosin VIIa dimer but not monomer transports the cargo molecules. Quite recently we found using single molecule analysis that human myosin VIIa is a very slow processive motor with a large step size. Recently, we have focused our effort on the function of myosin X in actin cytoskeletal rearrangement and filopodia formation. We showed that this myosin is a high duty ratio motor and moves processively on both single actin filaments and actin bundles when it forms a dimer. We found that full-length myosin X is a monomer with a folded inhibited structure which is extended when the molecule binds to phospholipids, and facilitates dimer formation and motor activation. Moreover, we found that the unique motor activity of myosin X is critical for filopodia induction and elongation, and found that myosin X induces multiple cycle of filopodia extension. Our findings suggest that myosin X is critical for filopodia and invadopodia formation of cancer cells for ECM degradation. Quite recently, we found myosin 19 associated with mitochondria directly move mitochondria and control mitochondrial movement and dynamics.
4. Function of motor proteins and cytoskeletal rearrangement during mesenchymal transition in cancer cells and lung epithelial cells.
Quite recently, I started to work on the function of motor proteins and cytoskeletal reorganization in mesenchymal transition of various cell types including breast cancer cells. In collaboration with lung injury group at UTHCT, we found that pleural epithelial cells directly contribute to pleural rind formation in a pleural injury. These cells change their phenotype to mesenchymal, which involves marked change in actin cytoskeletal structure and myosin and its regulatory protein expression. Moreover, we found that epithelial-mesenchymal transition induces invadosome formation, activation of metalloproteases and collagen transportation systems. More recently, we started to work on epithelial-mesenchymal transition (EMT) of human breast cancer cells. We found that milk exosomes induces EMT in both breast cancer and benign cells, based on the change in actin cytoskeletal structure and altered expression of α-SMA and E-cadherin. Breast milk exosomes containing high levels of TGFβ2 induce changes in both benign and malignant breast epithelial cells consistent with the development and progression of breast cancer, suggesting a role for high TGFβ2 expressing breast milk exosomes in influencing breast cancer risk.

Publications (selected out of 253 total)

1. Regulation of smooth muscle and non-muslce myosin II Ikebe, M., Reardon, S., Mitani, Y., Kamisoyama, H., Matsuura, M., and Ikebe, R. (1994) Involvement of the c-terminal residues of the 20,000 dalton light chain of myosin on the regulation of smooth muscle actomyosin. Proc. Natl. Acad. Sci. USA, 91, 9096-9100.
Sata, M., Stafford, W.F.III, Mabuchi, K., and Ikebe, M. (1997) The motor domain and the regulatory domain solely dictate enzymatic activity and phosphorylation dependent regulation of myosin, respectively. Proc. Natl. Acad. Sci. 94, 91-96.
Ikebe, M, Komatsu, S., Woodland, J., Ikebe, R., Craig, R.,# and Higashihara, M. (2001)The tip of the coiled-coil rod determines the filament formation of smooth muscle and non-muscle myosin. J. Biol. Chem. 276, 30293-30300.
Komatsu, S., and Ikebe, M. ZIP kinase is responsible for the phosphorylation of myosin II and necessary for cell motility in mammalian fibroblast cells. J. Cell Biol., 165, 243-254 (2004). PMCID: PMC2172045
Yang, S., Tiwari, P., Lee, K.H., Sato, O., Ikebe, M., Padron, R., and Craig, R. (2020) Cryo-EM structure of the inhibited (10S) form of myosin II. Nature, 588, 521-525.
2. Regulation of myosin phosphorylation in smooth muscle contraction and non-muscle cell migration such as cancer cells.
Ito, T., Ikebe, M., Kargacin, G., Hartshorne, D.J., Kemp, B., and Fay, F.S. Effects of modulators of myosin light chain kinase activity in single smooth muscle cells. Nature, 338, 164-167(1989).
Komatsu, S., and Ikebe, M. ZIP kinase is responsible for the phosphorylation of myosin II and necessary for cell motility in mammalian fibroblast cells. J. Cell Biol., 165, 243-254 (2004). PMCID: PMC2172045
Komatsu, S., and Ikebe, M. Phosphorylation of myosin II at the Ser1 and Ser2 is critical for normal PDGF-induced reorganization of myosin filaments. Mol. Biol. Cell, 18, 5081-5090 (2007). PMCID: PMC2096596
Nakamura, K., Koga, K., Sakai, H.,and Ikebe, M. cGMP dependent relaxation of smooth muscle is coupled with the phosphorylation of myosin phosphatase. Circ. Res., 101, 712-722 (2007)
Komatsu, S., and Ikebe, M. ZIPK is critical for the motility and contractility of VSMC through the regulation of Nonmuscle Myosin II isoforms. Am. J. Physiol. Heart and Circ. Physiol., 306, H1275-H1286 (2014) PMCID:PMC4010671
Shibata, K., Sakai, H., Huang, Q., Kamata, H.,Chiba, Y., Misawa, M., Ikebe, R., and Ikebe, M. Rac1 regulates myosin II phosphorylation through regulation of myosin light chain phosphatase. J. Cell Physiol., 230, 1352-1364 (2015)
Komatsu, S., Kitazawa, T., and Ikebe, M. (2017) Visualization of stimulus-specific heterogeneous activation of heterogenous activation of individual vascular smooth muscle cells in aortic tissues. J. Cell Physiol., 233, 434-446. PMCID:PMC5741290
Komatsu, S., Wang, L., Seow, C.Y., and Ikebe, M. (2020) p116rip promotes myosin phosphatase activity in airway smooth muscle cells – A switch toward a hyper contractile phenotype. J. Cell Physiol. 235, 114-127
3. Function and regulation of unconventional myosin and its function in actin cytoskeletal rearrangement
Li, X.-D., Jung, H.-S., Mabuchi, K., Craig, R., and Ikebe, M. The globular tail domain put on the brake to stop the ATPase cycle of myosin Va. Proc. Natl. Acad. Sci. U.S.A., 105:1140-1145 (2008). PMCID: PMC2234105
Umeki, N., Jung, H.S., Watanabe, S., Sakai, T., Li, X.D., Ikebe, R., Craig, R., and Ikebe, M. The tail binds to the head-neck domain, inhibiting ATPase activity of myosin VIIA. Proc. Natl. Acad. Sci. U.S.A., 106(21):8483-8488 (2009). PMCID: PMC2688991
Sun, Y., Sato, O., Ruhnow, F., Arsenault, M.E., Ikebe, M., and Goldman, Y.E. Single Molecule Stepping and Structural Dynamics of Myosin X, Nat. Struc. Mol. Biol., 17, 485-491 (2010). PMCID: PMC2867696
Sakai, T., Umeki, N., Ikebe, R., and Ikebe, M. Cargo binding activates myosin VIIA motor function in cells, Proc. Natl., Acad., Sci., U.S.A., 108:7028-7033 (2011). PMCID: PMC3084129
Umeki, N., Jung, H.-S., Sakai. T., Sato, O., Ikebe, R., and Ikebe, M. Phospholipid-dependent regulation of the motor activity of myosin X, Nat. Struc. Mol. Biol., 18:783-788 (2011).
Sakai, T., Jung, H-S., Sato, O., Yamada, M., You, D-Y., Ikebe, R., and Ikebe, M. (2015) Structure and regulation of the movement of human myosin VIIA. J. Biol. Chem., 290, 17587-17598. PMCID: PMC4498092
Sato, O., H.-S. Jung, Komatsu, S., Tsukasaki, Y., Watanabe, T. M., Homma, K., and Ikebe, M. (2017) Activated full-Length Myosin X moves processively on filopodia with large steps toward diverse two-dimensional directions. Sci. Reports, 7, 443237. PMCID: PMC5346999
Kamata, H., Tsukasaki, Y., Sakai, T., Ikebe, R., Wang, J., Jeffers, A., Owens, S., Suzuki, T., Higashihara, M., Idell, S., Tucker, T. A., and Ikebe, M. (2017) KIF5A transports collagen vesicles of myofibroblasts during pleural fibrosis. Sci. Reports, 7, 4556. PMCID:PMC5496869
Sato, O., Sakai, T., Ikebe, R., and Ikebe, M. (2017) Human myosin VIIa is a very slow processive motor protein on various cellular actin structures. J. Biol. Chem., 292, 10950-10960. PMCID:PMC5491779
Sato, O., Sakai, T., Choo, Y.Y., Ikebe, R., Watanabe, T., and Ikebe, M. (2022) Mitochondria associated myosin 19 processively transports mitochondria on actin track in living cells. J. Biol. Chem. 298,101883. PMCID: PMC9065997
4. Function of motor proteins and cytoskeletal rearrangement during mesenchymal transition in cancer cells and lung epithelial cells.
Philley, J.V., Kannan, A., Qin, W., Sauter, E.R., Ikebe, M., Hertweck, K.L., Troyer, D.A., Semmes, O.J., and Dasgupta, S. (2016) Complex-I Alteration and Enhanced Mitochondrial Fusion Are Associated With Prostate Cancer Progression. J. Cell Physiol., 231, 1364-1374
Kannan, A., Wells, R.B., Sivakumar, S., Komatsu, S., Singh, K.P., Samten, B., Philley, J.V., Sauter, E.R., Ikebe, M., Idell, S., Gupta, S., and Dasgupta, S. (2016) Mitochondrial Reprogramming Regulates Breast Cancer Progression. Clin. Cancer Res. 22, 3348-3360. PMCID:PMC3412716
Qin, W., Tsukasaki, Y., Dasgupta, S., Mukhopadhyay, N., Ikebe M., and Sauter, E.R. (2016) Exosomes in Human Breast Milk Promote EMT. Clin. Cancer Res., 22, 4517-1524. PMID: 27060153
Boren, J., Shryock, G., Fergis, A., Jeffers, A., Owens, S., Qin, W., Koenig, K.B., Tsukasaki, Y., Komatsu, S., Ikebe, M., Idell, S., and Tucker, T. (2017) Inhibition of glycogen synthetase kinase 3b blocks mesomesenchymal transition and attenuates streptococcus pneumonia-mediated pleural injury in mice. Am. J. Pathol. 187, 2461-2472. PMCID:PMC5809597
Tucker, T., Tsukasaki, Y., Sakai, T., Mitsuhashi, S., Komatsu, S., Jeffers, A., Idell, S., and Ikebe, M. (2019) Myocardin is involved in mesothelial-mesenchymal transition of human pleural mesothelial cells. Am. J. Respir. Cell Mol. Biol. Doi:10.1165/rcmb. 2018-0121OC [Epub ahead of print]
Choo, Y. Y., Sakai, T., Jeffers, A., Ikebe, R., Idell, S., Tucker, T.T., and Ikebe, M. (2022) Calponin contributes to myofibroblast defferentiation of human pleural mesothelial cells. Am. J. Physiol. Lung Cell Mol. Physiol. 322, L348-L364. Doi:10.1152/alplung.00289.2021
Sakai, T., Choo, Y,Y., Ikebe, R., Jeffers, A., Idell., S., Tucker, T.T., and Ikebe, M. (2022) Myosin 5B transports fibronectin containing vesicles and facilitates fibronectin secretion from human pleural mesothelial cells. Int. J. Mol. Sci. 23, 4823. doi: 10.3390/ijms23094823.