Human LACC1 increases innate receptor-induced responses and a LACC1 disease-risk variant modulates these outcomes

Abstract

Functional consequences for most inflammatory disease-associated loci are incompletely defined, including in the LACC1 (C13orf31) region. Here we show that human peripheral and intestinal myeloid-derived cells express laccase domain-containing 1 (LACC1); LACC1 is expressed in both the cytoplasm and mitochondria. Upon NOD2 stimulation of human macrophages, LACC1 associates with the NOD2-signalling complex, and is critical for optimal NOD2-induced signalling, mitochondrial ROS (mtROS) production, cytokine secretion and bacterial clearance. LACC1 constitutively associates with succinate dehydrogenase (SDH) subunit A, and amplifies pattern recognition receptor (PRR)-induced SDH activity, an important contributor to mtROS production. Relative to LACC1 Ile254, cells transfected with Crohn's disease-risk LACC1 Val254 or LACC1 with mutations of the nearby histidines (249,250) have reduced PRR-induced outcomes. Relative to LACC1 Ile254 carriers, Val254 disease-risk carrier macrophages demonstrate decreased PRR-induced mtROS, signalling, cytokine secretion and bacterial clearance. Therefore, LACC1 is critical for amplifying PRR-induced outcomes, an effect that is attenuated by the LACC1 disease-risk variant.

LACC1 Required for NOD2-Induced, ER Stress-Mediated Innate Immune Outcomes in Human Macrophages and LACC1 Risk Variants Modulate These Outcomes

“…Localizes to the ER While LACC1 is associated with multiple immune-mediated diseases, only a few recent studies have examined its function in mammalian cells. LACC1 has been shown to colocalize with the mitochondria, cytosol, and peroxisomes (Assadi et al, 2016;Cader et al, 2016;Lahiri et al, 2017). However, our in silico analysis by PSORTII indicated that LACC1 might also localize to the ER, and a THP-1 human macrophage cell line (unstimulated) study showed a low percentage of LACC1 localization to the ER (Assadi et al, 2016).…”

“…Using calnexin as an ER marker, a low level of LACC1 localization to the ER was observed at baseline in MDMs through a microscopic approach (Figures 1A and 1B). As LACC1 regulates PRR-induced outcomes (Lahiri et al, 2017), we asked if PRR stimulation regulates LACC1 localization to the ER. We stimulated NOD2, a PRR associated with Crohn's disease whose ligand is the minimal component of bacterial peptidoglycan, muramyl dipeptide (MDP).…”

“…We hypothesized that one such mechanism may involve proximal LACC1 signaling in the cytoplasm, whereas another may require direct LACC1 localization to the ER. Regarding the first hypothesis, we previously found that following NOD2 stimulation of human MDMs LACC1 associates with the NOD2 signaling complex (containing RIP2, IRAK1, TRAF6, phospho-ERK, phospho-p38, and phospho-IkBa) and contributes to its optimal assembly (Lahiri et al, 2017). A mouse macrophage MDMs were transfected with scrambled or LACC1 siRNAs.…”

“…Understanding the consequences of genetic variants associated with immune-mediated diseases can often lead to unexpected elucidation of mechanisms and pathways required for maintaining immune homeostasis. LACC1 genetic variants are associated with inflammatory bowel disease (IBD) (Jostins et al, 2012), leprosy (Liu et al, 2015), and juvenile arthritis (Wakil et al, 2015), yet only a limited number of studies has examined the functional consequences of mammalian laccase domain containing-1 (LACC1) protein and its variants (Assadi et al, 2016;Cader et al, 2016;Lahiri et al, 2017;Skon-Hegg et al, 2019). We and others found that the common LACC1 Ile254Val variant (allele frequency 0.226-0.245 in European ancestry individuals per the dbSNP) results in a loss of function as manifested by decreased cytokine secretion, bacterial clearance, ROS production, and fatty-acid oxidation in macrophages (Cader et al, 2016;Lahiri et al, 2017).…”

“…Subcellular localization can provide important insight into mechanisms through which proteins mediate their effects, with localization to multiple subcellular compartments allowing for proteins to carry out distinct functions at these respective sites (Yogev and Pines, 2011). Previous studies showed LACC1 localized to the cytosol, mitochondria, and/or peroxisomes in human macrophages (Assadi et al, 2016;Cader et al, 2016;Lahiri et al, 2017). However, our in silico analysis showing LACC1 localization to the ER and a prior study showing that a small percent of LACC1 may also localize to the ER in THP-1 cells under homeostatic conditions (Assadi et al, 2016) set the foundation for additional LACC1 mechanisms.…”