Centrioles control the capacity, but not the specificity, of cytotoxic T cell killing

Abstract

Immunological synapse formation between cytotoxic T lymphocytes (CTLs)and the target cells they aim to destroy is accompanied by reorientation of the CTL centrosome to a position beneath the synaptic membrane. Centrosome polarization is thought to enhance the potency and specificity of killing by driving lytic granule fusion at the synapse and thereby the release of perforin and granzymes toward the target cell. To test this model, we employed a genetic strategy to delete centrioles, the core structural components of the centrosome.Centriole deletion altered microtubule architecture, as expected, but surprisingly had no effect on lytic granule polarization and directional secretion. Nevertheless, CTLs lacking centrioles did display substantially reduced killing potential, which was associated with defects in both lytic granule biogenesis and synaptic actin remodeling. These results reveal an unexpected role for the intact centrosome in controlling the capacity, but not the specificity, of cytotoxic killing.

Mechanically active integrins direct cytotoxic secretion at the immune synapse

“…This behavior has long been attributed to the centrosome, which serves as a focal point for intracellular granules and polarizes toward the target cell during IS formation 2,4 . Studies from our group and others, however, indicate that the centrosome is dispensable for synaptic secretion, implying the existence of other targeting mechanisms [5][6][7] . Cytotoxic lymphocytes exert nanonewton scale forces across the IS that have been implicated in both the activation of mechanosensitive cell surface receptors and the potentiation of perforin function [8][9][10][11][12][13][14] .…”

“…That being said, our results do not exclude an important role for the centrosome and microtubules in enhancing the speed and efficiency of cytotoxic secretion. Indeed, we have shown that microtubule depletion, while failing to disrupt the directionality of degranulation, nevertheless profoundly reduces the magnitude of the secretory response 5 . Accordingly, we favor a model in which centrosome polarization delivers granules into the IS neighborhood, at which point their site of fusion is dictated by integrin licensing.…”

“…Although this mechanism is thought to promote polarized secretion, studies from multiple labs indicate that it is dispensable for the process [5][6][7] . Indeed, we have found that CTLs lacking a functional centrosome or even the entire microtubule cytoskeleton retain the capacity to release perforin and granzyme directionally into the IS 5 . The integrin licensing model described here explains these prior observations by providing an alternative targeting mechanism.…”

“…Target recognition induces the trafficking of lytic granules along microtubules toward the centrosome, which concomitantly reorients to a position just beneath the center of the IS, thereby positioning granules close to the synaptic membrane. Although this mechanism is thought to promote polarized secretion, studies from multiple labs indicate that it is dispensable for the process [5][6][7] . Indeed, we have found that CTLs lacking a functional centrosome or even the entire microtubule cytoskeleton retain the capacity to release perforin and granzyme directionally into the IS 5 .…”

Collagen density defines 3D migration of CTLs and their consequent cytotoxicity against tumor cells

“…In terms of the microtubule network, re-orientation of MTOC to the immunological synapse (IS) is a hallmark for CTL activation upon recognition of target cells, which plays a key role in enriching lytic granules towards the IS (Ritter et al, 2017; Yi et al, 2013). Perturbation of the microtubule architecture in CTLs results in reduced killing efficiency but does not affect degranulation (Tamzalit et al, 2020). In our work, although the microtubule network was disrupted by nocodazole (10 μM) to a large extent, the remaining was sufficient to support lytic granule release as shown in Supplemental Fig.…”