Background: LPS increases NALP3 levels, but the mechanisms remain unknown. Results: LPS prolongs the lifespan of NALP3 protein by reducing E3 ligase (SCF FBXL2 )-mediated ubiquitination. Conclusion: Proinflammatory cytokine release is reduced by a small molecule that restores cellular SCF FBXL2 levels. Significance: We identified a novel pathway of inflammasome priming that may serve as a springboard for future translational studies.

Inflammasomes regulate innate immune responses by facilitating maturation of inflammatory cytokines, interleukin (IL)-1β and IL-18. NACHT, LRR and PYD domains-containing protein 7 (NALP7) is one inflammasome constituent, but little is known about its cellular handling. Here we show a mechanism for NALP7 protein stabilization and activation of the inflammasome by Toll-like receptor (TLR) agonism with bacterial lipopolysaccharide (LPS) and the synthetic acylated lipopeptide Pam3CSK4. NALP7 is constitutively ubiquitinated and recruited to the endolysosome for degradation. With TLR ligation, the deubiquitinase enzyme, STAM-binding protein (STAMBP) impedes NALP7 trafficking to lysosomes to increase NALP7 abundance. STAMBP deubiquitinates NALP7 and STAMBP knockdown abrogates LPS or Pam3CSK4-induced increases in NALP7 protein. A small-molecule inhibitor of STAMBP deubiquitinase activity, BC-1471, decreases NALP7 protein levels and suppresses IL-1β release after TLR agonism. These findings describe a unique pathway of inflammasome regulation with the identification of STAMBP as a potential therapeutic target to reduce pro-inflammatory stress.

Idiopathic pulmonary fibrosis is a disease characterized by progressive, unrelenting lung scarring, with death from respiratory failure within 2-4 years unless lung transplantation is performed. New effective therapies are clearly needed. Fibroblast activation protein (FAP) is a cell surface-associated serine protease up-regulated in the lungs of patients with idiopathic pulmonary fibrosis as well as in wound healing and cancer. We postulate that FAP is not only a marker of disease but influences the development of pulmonary fibrosis after lung injury. In two different models of pulmonary fibrosis, intratracheal bleomycin instillation and thoracic irradiation, we find increased mortality and increased lung fibrosis in FAP-deficient mice compared with wild-type mice. Lung extracellular matrix analysis reveals accumulation of intermediate-sized collagen fragments in FAPdeficient mouse lungs, consistent with in vitro studies showing that FAP mediates ordered proteolytic processing of matrix metalloproteinase (MMP)-derived collagen cleavage products. FAP-mediated collagen processing leads to increased collagen internalization without altering expression of the endocytic collagen receptor, Endo180. Pharmacologic FAP inhibition decreases collagen internalization as expected. Conversely, restoration of FAP expression in the lungs of FAP-deficient mice decreases lung hydroxyproline content after intratracheal bleomycin to levels comparable with that of wild-type controls. Our findings indicate that FAP participates directly, in concert with MMPs, in collagen catabolism and clearance and is an important factor in resolving scar after injury and restoring lung homeostasis. Our study identifies FAP as a novel endogenous regulator of fibrosis and is the first to show FAP's protective effects in the lung.Idiopathic pulmonary fibrosis, the most common of the idiopathic interstitial pneumonias, is characterized by inexorable progressive lung injury and scarring, with eventual death within 2-4 years from the time of diagnosis in the absence of lung transplantation (1). The etiology of the disease is poorly understood, and current Food and Drug Administration-approved treatments have only limited impact on the course of the disease (2-4).Fibroblast activation protein (FAP, 2 also known as seprase) is a 95-kDa cell surface, type II integral serine protease belonging to the post-proline dipeptidyl aminopeptidase (DPP) family (5) that is specifically induced on lung fibroblasts in patients with idiopathic pulmonary fibrosis, in particular at the leading edge of fibrosis (6). The DPP family of serine proteases cleaves amino-terminal dipeptides from polypeptides with L-proline or L-alanine at the penultimate position. FAP is unique in that it displays additional in vitro endopeptidase (7), gelatinase, and potentially collagenase activity (8,9). FAP expression is restricted, occurring at high levels on mesenchymal cells during embryogenesis (10) and then is repressed shortly after birth. In conditions associated with matrix remodeling...

Signal regulatory protein ␣ (SIRP␣) is a membrane glycoprotein immunoreceptor abundant in cells of monocyte lineage. SIRP␣ ligation by a broadly expressed transmembrane protein, CD47, results in phosphorylation of the cytoplasmic immunoreceptor tyrosine-based inhibitory motifs, resulting in the inhibition of NF-B signaling in macrophages. Here we observed that proteolysis of SIRP␣ during inflammation is regulated by a disintegrin and metalloproteinase domain-containing protein 10 (ADAM10), resulting in the generation of a membrane-associated cleavage fragment in both THP-1 monocytes and human lung epithelia. We mapped a charge-dependent putative cleavage site near the membrane-proximal domain necessary for ADAM10-mediated cleavage. In addition, a secondary proteolytic cleavage within the membrane-associated SIRP␣ fragment by ␥-secretase was identified. Ectopic expression of a SIRP␣ mutant plasmid encoding a proteolytically resistant form in HeLa cells inhibited activation of the NF-B pathway and suppressed STAT1 phosphorylation in response to TNF␣ to a greater extent than expression of wild-type SIRP␣. Conversely, overexpression of plasmids encoding the proteolytically cleaved SIRP␣ fragments in cells resulted in enhanced STAT-1 and NF-B pathway activation. Thus, the data suggest that combinatorial actions of ADAM10 and ␥-secretase on SIRP␣ cleavage promote inflammatory signaling.Inhibitory receptors including signal regulatory protein ␣ (SIRP␣), 2 CD33, SIGLECs (sialic acid-binding immunoglobulin-type lectins), CD66a, PD-1, CD31, PILRa (paired immunoglobin-like type 2 receptor ␣), CMRF35H, gp49B1, PECAM1, and others have been demonstrated to suppress the initiation of inflammatory signaling and contribute to the resolution of inflammation after infection (1, 2). SIRP␣ is membrane glycoprotein immunoreceptor that is expressed mainly in myeloid and neuronal cells (3). Ligation of SIRP␣ results in phosphorylation of the cytoplasmic immunoreceptor tyrosine-based inhibitory motifs (ITIMs), which recruit and activate SH2 domain-containing phosphotyrosine phosphatases SHP-1 and SHP-2 (4). SIRP␣ signaling results in reduced macrophage migration and phagocytosis and inhibition of NF-B signaling with reduction of release of NF-B-dependent cytokines in macrophages (5, 6). Phosphorylation of SIRP␣ ITIM domains also enhances JAK/STAT activation and NADPH oxidase expression and activity (7). Thus, SIRP␣ serves as an important modulator of the host adaptive immune response. Proteolysis and release of the SIRP␣ NH 2 -terminal domain has been demonstrated in primary cultured neurons, melanoma cells, and macrophage cell lines. Cleavage of murine SIRP␣ through an MMP inhibitor-sensitive pathway was first observed in cultured cells engineered to express both SIRP␣ and an active form of Ras (8). In these cells, blocking SIRP␣ proteolysis resulted in inhibited cell migration, cell spreading, and cytoskeletal reorganization. In addition, SIRP␣ was shown to regulate synaptic activity through activation of MMP inhibitor-sensitive prote...