L-Threonine β-naphthylamide

CD38 is a cell surface receptor capable of generating calcium-mobilizing second messengers. It has been implicated in host defense and cancer biology, but signaling mechanisms downstream of CD38 remain unclear. Mutations in LRRK2 (leucine-rich repeat kinase 2) are the most common genetic cause of Parkinson disease; it is also a risk factor for Crohn disease, leprosy, and certain types of cancers. The pathogenesis of these diseases involves inflammation and macroautophagy/autophagy, processes both CD38 and LRRK2 are implicated in. Here, we mechanistically and functionally link CD38 and LRRK2 as upstream activators of TFEB (transcription factor EB), a host defense transcription factor and the master transcriptional regulator of the autophagy/lysosome machinery. In B-lymphocytes and macrophages, we show that CD38 and LRRK2 exist in a complex on the plasma membrane. Ligation of CD38 with the monoclonal antibody clone 90 results in internalization of the CD38-LRRK2 complex and its targeting to the endolysosomal system. This generates an NAADP-dependent calcium signal, which requires LRRK2 kinase activity, and results in the downstream activation of TFEB. lrrk2 KO macrophages accordingly have TFEB activation defects following CD38 or LPS stimulation and fail to switch to glycolytic metabolism after LPS treatment. In overexpression models, the pathogenic LRRK2G2019S mutant promotes hyperactivation of TFEB even in the absence of CD38, both by stabilizing TFEB and promoting its nuclear translocation via aberrant calcium signaling. In sum, we have identified a physiological CD38-LRRK2-TFEB signaling axis in immune cells. The common pathogenic mutant, LRRK2G2019S, appears to hijack this pathway.

The following aminopeptidase (AP) activities were found to be associated with the surface of mouse spleen cells: Leu-AP (138 pmol/10(5) cells X minute) and AP-B (16 pmol/10(5) cells X minute with Lys-beta-naphthylamide as substrate and 21 pmol/10(5) cells X minute with Arg-beta-naphthylamide substrate); AP-A activity was not detected by the assay system applied. The immunoactive peptide bestatin inhibited the Leu-AP, while AP-B activity decreased in the presence of both arphamenines A and B and bestatin. No effects on these enzymes were caused by amastatin (an AP-A inhibitor), FK-156, FK-565 and Bu-2743E; the latter peptide turned out to be not an inhibitor of cell surface associated microsomal Leu-AP but an inhibitor of cytosolic Leu-AP. The immunoactive peptides bestatin, arphamenines A and B, and amastatin increased [3H]thymidine incorporation into spleen cells containing lymphocytes and macrophages. These mitogenic actions were not observed when macrophages were removed from the cultures or the cells had been stimulated with ConA or LPS. The lactoyl- and heptanoyl peptides FK-156 and FK-565 caused a mitogenic action on lymphocytes independently of the presence of macrophages. The inhibitor of cytosolic Leu-AP did not change the incorporation into lymphocytes.

Lysosomal damage activates AMPK, a regulator of macroautophagy/autophagy and metabolism, and elicits a strong ubiquitination response. Here we show that the cytosolic lectin LGALS9 detects lysosomal membrane breach by binding to lumenal glycoepitopes, and directs both the ubiquitination response and AMPK activation. Proteomic analyses have revealed increased LGALS9 association with lysosomes, and concomitant changes in LGALS9 interactions with its newly identified partners that control ubiquitination-deubiquitination processes. An LGALS9-inetractor, deubiquitinase USP9X, dissociates from damaged lysosomes upon recognition of lumenal glycans by LGALS9. USP9X's departure from lysosomes promotes K63 ubiquitination and stimulation of MAP3K7/TAK1, an upstream kinase and activator of AMPK hitherto orphaned for a precise physiological function. Ubiquitin-activated MAP3K7/TAK1 controls AMPK specifically during lysosomal injury, caused by a spectrum of membrane-damaging or -permeabilizing agents, including silica crystals, the intracellular pathogen Mycobacterium tuberculosis, TNFSF10/TRAIL signaling, and the anti-diabetes drugs metformin. The LGALS9-ubiquitin system activating AMPK represents a novel signal transduction system contributing to various physiological outputs that are under the control of AMPK, including autophagy, MTOR, lysosomal maintenance and biogenesis, immunity, defense against microbes, and metabolic reprograming.