Plasminogen activator inhibitor 1 (PAI1) promotes actin cytoskeleton reorganization and glycolytic metabolism in triple negative breast cancer
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ABSTRACT: Plasminogen activator inhibitor 1 (PAI1) promotes actin cytoskeleton reorganization and glycolytic metabolism in triple negative breast cancer
Project description:Migration and invasion of cancer cells constitute fundamental processes in tumor progression and metastasis. Migratory cancer cells commonly upregulate expression of plasminogen activator inhibitor 1 (PAI1), and PAI1 correlates with poor prognosis in breast cancer. However, mechanisms by which PAI1 promotes migration of cancer cells remain incompletely defined. Here we show that increased PAI1 drives rearrangement of the actin cytoskeleton, mitochondrial fragmentation, and glycolytic metabolism in triple-negative breast cancer (TNBC) cells. In two-dimensional environments, both stable expression of PAI1 and treatment with recombinant PAI1 increased migration, which could be blocked with the specific inhibitor tiplaxtinin. PAI1 also promoted invasion into the extracellular matrix from coculture spheroids with human mammary fibroblasts in fibrin gels. Elevated cellular PAI1 enhanced cytoskeletal features associated with migration, actin-rich migratory structures, and reduced actin stress fibers. In orthotopic tumor xenografts, we discovered that TNBC cells with elevated PAI1 show collagen fibers aligned perpendicular to the tumor margin, an established marker of invasive breast tumors. Further studies revealed that PAI1 activates ERK signaling, a central regulator of motility, and promotes mitochondrial fragmentation. Consistent with known effects of mitochondrial fragmentation on metabolism, fluorescence lifetime imaging microscopy of endogenous NADH showed that PAI1 promotes glycolysis in cell-based assays, orthotopic tumor xenografts, and lung metastases. Together, these data demonstrate for the first time that PAI1 regulates cancer cell metabolism and suggest targeting metabolism to block motility and tumor progression. IMPLICATIONS: We identified a novel mechanism through which cancer cells alter their metabolism to promote tumor progression.
Project description:SMCs express plasminogen activator inhibitor-1 (PAI-1), which regulates SMC function and vascular remodeling. However, whether PAI-1 controls SMC cytoskeletal dynamics and stiffness is unknown, and the causal role of PAI-1 in arterial stiffening is undefined. SMCs from human coronary arteries and aortae of wild-type vs. PAI-1-deficient mice were cultured with or without PAI-039, a specific PAI-1 inhibitor, after which cell stiffness was measured by atomic force microscopy, filamentous actin structures were assessed by confocal microscopy, and the activities cofilin, LIM domain kinase 1 (LIMK), slingshot homolog 1 (SSH), and AMP-activated protein kinase (AMPK) were measured. RNA sequencing was performed to determine the effects of PAI-039 on SMC gene expression. Effects of PAI-039 on aortic stiffness were assessed by pulse wave velocity. PAI-039 significantly reduced intrinsic stiffness of human SMCs, which was accompanied by significant decreases in cytoplasmic actin filaments. Similar effects were observed in wild-type, but not in PAI-1-deficient SMCs. Mechanistically, PAI-039 significantly increased the activity of cofilin, an actin depolymerase, in SMCs expressing PAI-1, but not in PAI-1-deficient cells. PAI-039 had no significant effects on LIMK or SSH activity. RNA-sequencing analysis suggested that PAI-039 up-regulates AMPK signaling in SMCs, which was confirmed by western blotting. Inhibition of AMPK prevented activation of cofilin by PAI-039. In mice, PAI-039 significantly decreased aortic stiffness without significantly altering peri-aortic fibrosis. PAI-039 decreases intrinsic SMC stiffness by reducing cytoplasmic stress fiber content. These effects are mediated by AMPK-dependent activation of cofilin. PAI-039 also decreases aortic stiffness in vivo. These findings suggest that PAI-1 is an important regulator of the SMC cytoskeleton and that pharmacologic inhibition of PAI-1 has potential to treat cardiovascular diseases mediated by accelerated arterial stiffening.
Project description:Spermatogenesis is a biological process within the testis that produces haploid spermatozoa for the continuity of species. Sertoli cells are somatic cells in the seminiferous epithelium that orchestrate spermatogenesis. Cyclic reorganization of Sertoli cell actin cytoskeleton is vital for spermatogenesis but the underlying mechanism remains largely unclear. Here we report that RNA-binding protein PTBP1 controls Sertoli cell actin cytoskeleton reorganization by programming alternative splicing of actin cytoskeleton regulators. This splicing control enables ectoplasmic specializations, the actin-based adhesion junctions, to maintain the blood-testis barrier and support spermatid transport and transformation. Of particular, we show that PTBP1 promotes actin bundle formation by repressing the inclusion of exon 14 of Tnik, a kinase present at the ectoplasmic specialization. Our results thus reveal a novel mechanism wherein Sertoli cell actin cytoskeleton dynamics is controlled post-transcriptionally by utilizing functionally distinct isoforms of actin regulatory proteins and PTBP1 is a key player in generating such isoforms.
Project description:We describe a new mutant allele of the ACTIN2 gene with enhanced actin dynamics, displaying a broad array of twisting and bending phenotypes that resemble BR-treated plants. Moreover, auxin transcriptional regulation is enhanced on the mutant background, supporting the idea that shaping actin filaments is sufficient to modulate BR-mediated auxin responsiveness. The actin cytoskeleton thus functions as a scaffold for integration of auxin and BR signaling pathways.
Project description:We describe a new mutant allele of the ACTIN2 gene with enhanced actin dynamics, displaying a broad array of twisting and bending phenotypes that resemble BR-treated plants. Moreover, auxin transcriptional regulation is enhanced on the mutant background, supporting the idea that shaping actin filaments is sufficient to modulate BR-mediated auxin responsiveness. The actin cytoskeleton thus functions as a scaffold for integration of auxin and BR signaling pathways. Three biological replicates were performed for each sample (wild-type and actin2-5) and hybridized to the the Affymetrix ATH1 GeneChips.
Project description:Cell-cell fusion is a frequent and essential event during development, and its dysregulation causes diseases ranging from infertility to muscle weakness. Fusing cells repeatedly need to remodel their plasma membrane by orchestrated formation and disassembly of cortical actin filaments, but how the dynamic reorganization of the actin cytoskeleton control is still poorly understood. Here, we identified a ubiquitin- dependent toggle switch that establishes reversible actin bundling during mammalian cell fusion. We found that EPS8-IRSp53 complexes stabilize cortical actin bundles at sites of cell contact, which in part pushes cells towards each other. Conversely, EPS8 monoubiquitylation by CUL3KCTD10 displaces EPS8-IRSp53 from membranes and counteracts actin bundling, a dual activity that allows apposed cells to progress with fusion. We conclude that cytoskeletal rearrangements during development are precisely controlled by ubiquitylation, raising the possibility to modulate the efficiency of cell-cell fusion for therapeutic benefit.