Regulation of Epithelial Cytokinesis and Cell-Cell Junctions by MgcRacGAP.

MgcRacGAP;Cytokinesis;Rho GTPase;cell-cell junction structure;Epithelial tissue;Xenopus laevis;Molecular;Cellular and Developmental Biology;Science;Cellular and Molecular Biology

Breznau, Elaina B.Csankovszki, Gyorgyi ;

University of Michigan

关键词: MgcRacGAP;    Cytokinesis;    Rho GTPase;    cell-cell junction structure;    Epithelial tissue;    Xenopus laevis;    Molecular;    Cellular and Developmental Biology;    Science;    Cellular and Molecular Biology;   

Others  :  https://deepblue.lib.umich.edu/bitstream/handle/2027.42/120908/ebreznau_1.pdf?sequence=1&isAllowed=y

瑞士|英语

来源: The Illinois Digital Environment for Access to Learning and Scholarship

【 摘 要 】

Localized activation of Rho GTPases is essential for multiple cellular functions, including cytokinesis and formation and maintenance of cell-cell junctions. Centralspindlin, a heterotetrameric complex composed of the kinesin MKLP1 and the GTPase Activating Protein (GAP), MgcRacGAP (Mgc), is required for the proper regulation of both processes. Although Mgc is required for spatially confined RhoA-GTP at the equatorial cortex of dividing cells, the target specificity of Mgc’s GAP activity, whether Mgc’s GAP activity is phospho-regulated, how Mgc is stabilized at microtubule plus ends, and how Mgc functions at cell-cell junctions remained unclear. We investigated Mgc’s role in the regulation of RhoA-GTP and Rac1-GTP in the intact vertebrate epithelium of Xenopus laevis embryos and in cultured cells using a combination of fluorescence microscopy, molecular biology, and biochemical assays. We show that Mgc’s GAP activity spatially restricts accumulation of both RhoA-GTP and Rac1-GTP in epithelial cells – RhoA at the cleavage furrow and RhoA and Rac1 at cell-cell junctions. Phosphorylation at serine 386 within Mgc’s GAP domain is not required for GTPase specificity, but functional Mgc GAP activity is required for successful cytokinesis. We found that Mgc is localized to the plus ends of individual equatorial astral microtubules during cytokinesis in Xenopus embryos, and identified a putative SxIP motif in Xenopus Mgc, which promotes co-localization with EB1 and microtubule plus end stability. Mutation of Mgc’s SxIP motif resulted in loss of Mgc tracking on growing microtubule plus ends, abnormal astral microtubule organization, and severe cytokinesis defects resulting from misregulated RhoA-GTP accumulation. Further, we found that Mgc localizes to adherens junctions in polarized epithelial cells via its SxIP motif and regulates adherens junction structure and integrity through modulation of RhoA signaling. Together, these results indicate that Mgc has GAP activity toward both RhoA and Rac1 at spatially distinct cellular locations, and that proper localization of Mgc is dependent upon its ability to be tethered at microtubule plus ends via the SxIP motif. Our data provide novel mechanistic insight into the regulation of Rho family GTPases in epithelial tissues, which is important for improving our understanding of signaling pathways that regulate epithelial pathologies.