Non-canonical activation of the ER stress sensor ATF6 by Legionella pneumophila effectors.

Nnejiuwa U Ibe,Shaeri Mukherjee,Advait Subramanian

doi:10.26508/lsa.202101247

Nnejiuwa U Ibe, Shaeri Mukherjee + Show 1 more

Open Access

https://doi.org/10.26508/lsa.202101247

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Abstract

The intracellular bacterial pathogen Legionella pneumophila (L.p.) secretes ∼330 effector proteins into the host cell to sculpt an ER-derived replicative niche. We previously reported five L.p. effectors that inhibit IRE1, a key sensor of the homeostatic unfolded protein response (UPR) pathway. In this study, we discovered a subset of L.p. toxins that selectively activate the UPR sensor ATF6, resulting in its cleavage, nuclear translocation, and target gene transcription. In a deviation from the conventional model, this L.p-dependent activation of ATF6 does not require its transport to the Golgi or its cleavage by the S1P/S2P proteases. We believe that our findings highlight the unique regulatory control that L.p exerts upon the three UPR sensors and expand the repertoire of bacterial proteins that selectively perturb host homeostatic pathways.

Highlights

Several intracellular pathogens, including Legionella pneumophila (L.p.), expertly manipulate host cell function to create their replicative niche
And in contrast to DTT treatment, infecting these cells with wild type L.p. (WT L.p.) resulted in the near complete processing of endogenous activating transcription factor-6 (ATF6)-FL into two distinct fragments—a major fragment of ~75 kD that we designate as ATF6-P (WT L.p. lane, Fig 1A) and a minor fragment of ~30 kD that we designate as ATF6-LMW (WT L.p. lane, Fig 1A, see high exposure)
Upon monitoring the localization of an N-terminal GFP tagged ATF6 fusion protein (GFP-ATF6-FL, see Fig S1A) in FcγR expressing Cos7 cells by confocal microscopy, we observed a substantial recruitment of ATF6 to the Legionella-containing vacuole (LCV) membrane with over 80% of LCVs marked positive for ATF6 (Fig S1B)

Summary

Introduction

Several intracellular pathogens, including Legionella pneumophila (L.p.), expertly manipulate host cell function to create their replicative niche. L.p. uses its effectors to prevent fusion of the Legionella-containing vacuole (LCV) with the host endosomal machinery. Instead these effectors facilitate the remodeling of the LCV into a compartment that supports pathogen replication (Marra et al, 1992; Roy et al, 1998; Wiater et al, 1998). Fusion with lysosomes is evaded during infection, there is substantial interaction between the LCV and other host organelles including the ER (Horwitz & Silverstein, 1983; Swanson & Isberg, 1995; Tilney et al, 2001). The ER–LCV interactions take on different forms as LCV maturation progresses

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