Lymphocyte signaling converges on microtubules

A B-cell actomyosin arc network couples integrin co-stimulation to mechanical force-dependent immune synapse formation

B-cell activation and immune synapse (IS) formation with membrane-bound antigens are actin-dependent processes that scale positively with the strength of antigen-induced signals. Importantly, ligating the B-cell integrin, LFA-1, with ICAM-1 promotes IS formation when antigen is limiting. Whether the actin cytoskeleton plays a specific role in integrin-dependent IS formation is unknown. Here, we show using super-resolution imaging of mouse primary B cells that LFA-1:ICAM-1 interactions promote the formation of an actomyosin network that dominates the B-cell IS. This network is created by the formin mDia1, organized into concentric, contractile arcs by myosin 2A, and flows inward at the same rate as B-cell receptor (BCR):antigen clusters. Consistently, individual BCR microclusters are swept inward by individual actomyosin arcs. Under conditions where integrin is required for synapse formation, inhibiting myosin impairs synapse formation, as evidenced by reduced antigen centralization, diminished BCR signaling, and defective signaling protein distribution at the synapse. Together, these results argue that a contractile actomyosin arc network plays a key role in the mechanism by which LFA-1 co-stimulation promotes B-cell activation and IS formation.

Selenium nanoparticles as new strategy to potentiate γδ T cell anti-tumor cytotoxicity through upregulation of tubulin-α acetylation

Immune cell therapy presents a paradigm for the treatment of malignant tumors. Human Vγ9Vδ2 T cells, a subset of peripheral γδ T cells, have been shown to have promising anti-tumor activity. However, new methodology on how to achieve a stronger anti-tumor activity of Vγ9Vδ2 T cells is under continuous investigation. In this work, we used selenium nanoparticles (SeNPs) to strengthen the anti-tumor cytotoxicity of Vγ9Vδ2 T cells. We found SeNPs pretreated γδ T cells had significantly stronger cancer killing and tumor growth inhibition efficacy when compared with γδ T cells alone. Simultaneously, SeNPs pretreatment could significantly upregulate the expression of cytotoxicity related molecules including NKG2D, CD16, and IFN-γ, meanwhile, downregulate PD-1 expression of γδ T cells. Importantly, we observed that SeNPs promoted tubulin acetylation modification in γδ T cells through interaction between microtubule network and lysosomes since the latter is the primary resident station of SeNPs shown by confocal visualization. In conclusion, SeNPs could significantly potentiate anti-tumor cytotoxicity of Vγ9Vδ2 T cells, and both cytotoxicity related molecules and tubulin acetylation were involved in fine-tuning γδ T cell toxicity against cancer cells. Our present work demonstrated a new strategy for further enhancing anti-tumor cytotoxicity of human Vγ9Vδ2 T cells by using SeNPs-based nanotechnology, not gene modification, implicating SeNPs-based nanotechnology had a promising clinical perspective in the γδ T cell immunotherapy for malignant tumors.

Actin depletion initiates events leading to granule secretion at the immunological synapse

Cytotoxic T lymphocytes (CTLs) use polarized secretion to rapidly destroy virally infected and tumor cells. To understand the temporal relationships between key events leading to secretion, we used high-resolution 4D imaging. CTLs approached targets with actin-rich projections at the leading edge, creating an initially actin-enriched contact with rearward-flowing actin. Within 1 min, cortical actin reduced across the synapse, T cell receptors (TCRs) clustered centrally to form the central supramolecular activation cluster (cSMAC), and centrosome polarization began. Granules clustered around the moving centrosome within 2.5 min and reached the synapse after 6 min. TCR-bearing intracellular vesicles were delivered to the cSMAC as the centrosome docked. We found that the centrosome and granules were delivered to an area of membrane with reduced cortical actin density and phospholipid PIP2. These data resolve the temporal order of events during synapse maturation in 4D and reveal a critical role for actin depletion in regulating secretion.

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4D imaging elucidates the order of events leading to secretion

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Actin depletion initiates events leading to centrosome polarization and secretion

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Lattice light-sheet imaging reveals a rearward flow of actin away from the synapse

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Both centrosome and granules are delivered to an area of membrane depleted of actin

Mechanical regulation of T-cell functions

T cells are key players of the mammalian adaptive immune system. They experience different mechanical microenvironments during their life cycle, from the thymus, secondary lymph organs, and peripheral tissues that are free of externally applied force, but display variable substrate rigidities to the blood and lymphatic circulation systems, where complicated hydrodynamic forces are present. Regardless of whether T cells are subject to external forces or generate their own internal forces, they respond and adapt to different biomechanical cues to modulate their adhesion, migration, trafficking, and triggering of immune functions through mechanical regulation of various molecules that bear force. These include adhesive receptors, immunoreceptors, motor proteins, cytoskeletal proteins, and their associated molecules. Here, we discuss the forces acting on various surface and cytoplasmic proteins of a T cell in different mechanical milieus. We review existing data on how force regulates protein conformational changes and interactions with counter molecules, including integrins, actin, and the T-cell receptor, and how each relates to T-cell functions.

Androgen receptor on the move: boarding the microtubule expressway to the nucleus

Recent studies have shown that the microtubule-stabilizing drug paclitaxel, which is commonly used for the treatment of prostate cancer, inhibits signaling from the androgen receptor by inhibiting its nuclear accumulation downstream of microtubule stabilization. This mechanism is independent of paclitaxel-induced mitotic arrest and could provide an alternative mechanism of drug action that can explain its clinical activity. In this review, we highlight the importance of signaling and trafficking pathways that depend on intact and dynamic microtubules, and, as such, they represent downstream targets of microtubule inhibitors. We showcase prostate cancer, which is driven by the activity of the androgen receptor, as recent reports have revealed a connection between the microtubule-dependent trafficking of the androgen receptor and the clinical efficacy of taxanes. Identification and further elucidation of microtubule-dependent tumor-specific pathways will help us better understand the molecular basis of clinical taxane resistance as well as to identify individual patients more likely to respond to treatment.

Human T lymphotropic virus type 1 increases T lymphocyte migration by recruiting the cytoskeleton organizer CRMP2

Recruitment of virus-infected T lymphocytes into the CNS is an essential step in the development of virus-associated neuroinflammatory diseases, notably myelopathy induced by retrovirus human T leukemia virus-1 (HTLV-1). We have recently shown the key role of collapsin response mediator protein 2 (CRMP2), a phosphoprotein involved in cytoskeleton rearrangement, in the control of human lymphocyte migration and in brain targeting in animal models of virus-induced neuroinflammation. Using lymphocytes cloned from infected patients and chronically infected T cells, we found that HTLV-1 affects CRMP2 activity, resulting in an increased migratory potential. Elevated CRMP2 expression accompanies a higher phosphorylation level of CRMP2 and its more pronounced adhesion to tubulin and actin. CRMP2 forms, a full length and a shorter, cleaved one, are also affected. Tax transfection and extinction strategies show the involvement of this viral protein in enhanced full-length and active CRMP2, resulting in prominent migratory rate. A role for other viral proteins in CRMP2 phosphorylation is suspected. Full-length CRMP2 confers a migratory advantage possibly by preempting the negative effect of short CRMP2 we observe on T lymphocyte migration. In addition, HTLV-1-induced migration seems, in part, supported by the ability of infected cell to increase the proteosomal degradation of short CRMP2. Finally, gene expression in CD69(+) cells selected from patients suggests that HTLV-1 has the capacity to influence the CRMP2/PI3K/Akt axis thus to positively control cytoskeleton organization and lymphocyte migration. Our data provide an additional clue to understanding the infiltration of HTLV-1-infected lymphocytes into various tissues and suggest that the regulation of CRMP2 activity by virus infection is a novel aspect of neuroinflammation.

Actin retrograde flow and actomyosin II arc contraction drive receptor cluster dynamics at the immunological synapse in Jurkat T cells

Actin and myosin IIA have been implicated in the inward movement of receptor clusters at the immunological synapse of T lymphocytes. This study defines their spatial organization and quantifies their relative contributions to the dynamics of receptor clusters at the immunological synapse.

Actin retrograde flow and actomyosin II contraction have both been implicated in the inward movement of T cell receptor (TCR) microclusters and immunological synapse formation, but no study has integrated and quantified their relative contributions. Using Jurkat T cells expressing fluorescent myosin IIA heavy chain and F-tractin—a novel reporter for F-actin—we now provide direct evidence that the distal supramolecular activation cluster (dSMAC) and peripheral supramolecular activation cluster (pSMAC) correspond to lamellipodial (LP) and lamellar (LM) actin networks, respectively, as hypothesized previously. Our images reveal concentric and contracting actomyosin II arcs/rings at the LM/pSMAC. Moreover, the speeds of centripetally moving TCR microclusters correspond very closely to the rates of actin retrograde flow in the LP/dSMAC and actomyosin II arc contraction in the LM/pSMAC. Using cytochalasin D and jasplakinolide to selectively inhibit actin retrograde flow in the LP/dSMAC and blebbistatin to selectively inhibit actomyosin II arc contraction in the LM/pSMAC, we demonstrate that both forces are required for centripetal TCR microcluster transport. Finally, we show that leukocyte function–associated antigen 1 clusters accumulate over time at the inner aspect of the LM/pSMAC and that this accumulation depends on actomyosin II contraction. Thus actin retrograde flow and actomyosin II arc contraction coordinately drive receptor cluster dynamics at the immunological synapse.