IFT20 regulates TFEB-dependent lytic granule biogenesis in cytotoxic T lymphocytes by orchestrating the MPR-dependent transport of granzyme B

TL;DR

This study shows that IFT20 helps build lytic granules in immune cells by managing the transport of granzyme B, which is crucial for killing infected or cancerous cells.

Contribution

IFT20 is identified as a novel regulator of lytic granule biogenesis in cytotoxic T cells via MPR-dependent transport and TFEB-dependent gene regulation.

Findings

IFT20 is essential for MPR recycling and granzyme B localization to lytic granules.

IFT20 deficiency reduces cytotoxic T cell killing ability but increases lysosomal and cytotoxic gene expression.

TFEB regulates both lysosomal and lytic granule genes, linking IFT20 to broader gene expression programs in CTLs.

Abstract

Cytotoxic T lymphocytes (CTL) exploit specialized secretory lysosomes, the lytic granules (LG) to kill target cells. The LGs carry a battery of apoptosis-inducing molecules enriched in granzymes (GZM), perforin and FasL, which are released at the immune synapse formed by CTLs with their cognate targets. Recent studies have revealed an unexpected diversity among LGs, suggesting the existence of multiple vesicular trafficking pathways in their biogenesis and exocytosis. We have previously implicated the ciliary protein IFT20 in the retrograde trafficking of the cation-independent mannose-6-phosphate receptor (MPR), which is required for the lysosomal targeting of the acid hydrolases. Here we investigate the role of IFT20 in LG biogenesis in CTLs, showing that IFT20 is essential for MPR recycling to the trans-Golgi network and ensures proper granzyme B (GZMB) localization to LGs. As a result, IFT20 deficiency impairs the killing capability of CTLs. In turn, to rescue the lysosome and LG defects, IFT20-deficient CTLs expresses higher levels of lysosomal genes and of components of the cytotoxic machinery of LGs. Interestingly, an in silico analysis suggests a transcriptional co-regulation of lysosome and LG genes by the master regulator of lysosome biogenesis TFEB. Accordingly, modulation of TFEB results in alterations in the expression of LG-related genes and CTL-mediated cytotoxicity. Collectively, our results identify IFT20 as a new player in the trafficking pathways that regulate LG biogenesis and highlight the existence in CTLs of an extended gene expression program regulated by TFEB, downstream of IFT20.

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