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Myosin 18A coassembles with nonmuscle myosin 2 to form mixed bipolar filaments.

ABSTRACT: Class-18 myosins are most closely related to conventional class-2 nonmuscle myosins (NM2). Surprisingly, the purified head domains of Drosophila, mouse, and human myosin 18A (M18A) lack actin-activated ATPase activity and the ability to translocate actin filaments, suggesting that the functions of M18A in vivo do not depend on intrinsic motor activity. M18A has the longest coiled coil of any myosin outside of the class-2 myosins, suggesting that it might form bipolar filaments similar to conventional myosins. To address this possibility, we expressed and purified full-length mouse M18A using the baculovirus/Sf9 system. M18A did not form large bipolar filaments under any of the conditions tested. Instead, M18A formed an ∼ 65-nm-long bipolar structure with two heads at each end. Importantly, when NM2 was polymerized in the presence of M18A, the two myosins formed mixed bipolar filaments, as evidenced by cosedimentation, electron microscopy, and single-molecule imaging. Moreover, super-resolution imaging of NM2 and M18A using fluorescently tagged proteins and immunostaining of endogenous proteins showed that NM2 and M18A are present together within individual filaments inside living cells. Together, our in vitro and live-cell imaging data argue strongly that M18A coassembles with NM2 into mixed bipolar filaments. M18A could regulate the biophysical properties of these filaments and, by virtue of its extra N- and C-terminal domains, determine the localization and/or molecular interactions of the filaments. Given the numerous, fundamental cellular and developmental roles attributed to NM2, our results have far-reaching biological implications.

SUBMITTER: Billington N

PROVIDER: S-EPMC8760901 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:The objective of the study was to understand how estrogen modulates the rigidity of the cytoskeleton in epithelial cells. Estrogen depletion decreased, and treatment with 17beta-estradiol increased deformability of cervical-vaginal epithelial cells. Estrogen also induced redistribution of nonmuscle myosin II-B (NMM-II-B); lesser interaction of NMM-II-B with actin; increased phosphorylation of NMM-II-B-heavy chains at threonine and serine residues; and decreased filamentation of NMM-II-B in vitro. The effects of 17beta-estradiol were time and dose related and could be mimicked by diethylstilbestrol. The effects of estrogen were blocked by cotreatment with antisense oligonucleotide for the estrogen receptor-alpha and inhibited by ICI-182,780 and tamoxifen; omission of epithelial growth factor (EGF) from the culture medium; and cotreatments with the EGF receptor inhibitor AG1478, the ERK-MAPK inhibitor PD98059, the casein kinase-II (CK2) inhibitor 5,6-dichloro-1-beta-(D)-ribofuranosylbenzimidazole, the Rho-associated kinase inhibitor Y-27632, and the nonspecific phosphatase inhibitor okadaic acid. Coadministration of 5,6-dichloro-1-beta-(D)-ribofuranosylbenzimidazole plus okadaic acid blocked the 17beta-estradiol effect. H-89 or LY294002 did not significantly affect estrogen effects. Treatment with estrogen increased activation of ERK1/2 and CK2 activity. These data suggest a novel pathway of estrogen regulation of the cytoskeleton in epithelial cells. The effect is mediated by estrogen receptor-alpha and involves in part the EGF-EGF receptor and ERK-MAPK cascades as proximal signaling networks and the CK2 and Rho-associated kinase-regulated myosin heavy chain phosphatase as terminal effectors. Augmented phosphorylation of NMM-II-B can block filamentation and induce disassociation of the myosin from the cortical actin, and disruption of the actomyosin ring can increase cell deformability. This mechanism can explain estrogen regulation of paracellular permeability in cervical-vaginal epithelia in vivo.

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Myosin 18A coassembles with nonmuscle myosin 2 to form mixed bipolar filaments.

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