Mst1 Kinase Regulates the Actin-Bundling Protein L-Plastin To Promote T Cell Migration

Abstract

Exploring the mechanisms controlling lymphocyte trafficking is essential for understanding the function of the immune system and the pathophysiology of immunodeficiencies. The Ste20/Mst1 kinase has been identified as a critical signaling mediator of T cell migration, and loss of Mst1 results in immunodeficiency disease. While Mst1 is known to support T cell migration through induction of cell polarization and lamellipodial formation, the downstream effectors of Mst1 are incompletely defined. Mice deficient for the actin-bundling protein L-plastin (LPL) have phenotypes similar to mice lacking Mst1, including decreased T cell polarization, lamellipodial formation and cell migration. We therefore asked whether LPL functions downstream of Mst1. The regulatory N-terminal domain of LPL contains a consensus Mst1 phosphorylation site at Thr89. We found that Mst1 can phosphorylate LPL in vitro and that Mst1 can interact with LPL in cells. Removal of the Mst1 phosphorylation site by mutating Thr89 to Ala impaired localization of LPL to the actin-rich lamellipodia of T cells. Expression of the T89A LPL mutant failed to restore migration of LPL-deficient T cells in vitro. Furthermore, expression of T89A LPL in LPL-deficient hematopoietic cells, using bone marrow chimeras, failed to rescue the phenotype of decreased thymic egress. These results identify LPL as a key effector of Mst1 and establish a novel mechanism linking a signaling intermediate to an actin-binding protein critical to T cell migration.

MST1/Hippo promoter gene methylation predicts poor survival in patients with malignant pleural mesothelioma in the IFCT-GFPC-0701 MAPS Phase 3 trial

“…By mimicking MST1 loss in mesothelioma cell lines via MST1 RNA interference (RNAi) transfection, we demonstrated that MST1 prevented nuclear YAP accumulation while permitting TAZ cytoplasmic retention in mesothelial cells, thus inhibiting cell motility, growth without anchorage, and proliferation, while controlling basal apoptosis. These results are consistent with data from the literature, where MST1 role in invasion, migration, apoptosis, and cell proliferation has already been documented in various cancer models, 15 , 16 , 32 – 35 though not yet in MPM. Moreover, MST1 or MST2 loss is known to lead to hyperproliferation and tumourigenesis, which are commonly prevented by concurrent YAP inactivation.…”

“… 5 MST1/2 kinases were also reported as contributing to the regulation of (i) apoptosis by establishing a complex with RASSF1A and CNK1 proteins 6 , 7 or with the apoptosis-inhibiting protein kinase CK2, 8 (ii) cell-cycle progression by catalysing the mitotic phosphorylation of MOBKL1A/1B, 9 – 13 and (iii) migration/invasion processes by stabilising lamellipodial F-actin. 14 – 16 …”

L-Plastin deficiency produces increased trabecular bone due to attenuation of sealing ring formation and osteoclast dysfunction

“…LPL phosphorylation is regulated by signaling pathways consisting of different kinases including PKC, PKA, Src, etc. 21,46,[60][61][62][63][64] The results presented here validate our previous studies 2,18-20 that LPL phosphorylation is essential in the regulation of NSZ formation by TNF-α signaling. A limitation of our study is that we did not explore the mechanisms regulating LPL phosphorylation.…”

Targeted deletion of the zebrafish actin-bundling protein L-plastin (lcp1)

“…In mammals, the phosphorylation of Ser5, Ser7 or both is known to increase L-plastin localization to the cytoskeleton, filament-bundling activity and the invasiveness of both melanoma and breast cancer cell lines [ 20 , 21 , 37 , 38 ]. Zebrafish, mouse and human L-plastin do share a threonine at position 89 (T89), a confirmed site of Mst1 phosphorylation [ 39 , 40 ]. Finally, all three sequences have an identical 14-amino acid calmodulin- binding domain ( ), suggesting conserved regulation by this calcium-binding protein [ 41 ].…”