Lysosomal protease deficiency or substrate overload induces an oxidative-stress mediated STAT3-dependent pathway of lysosomal homeostasis

How cells regulate their lysosomal proteolytic capacity is only partly understood. Here, the authors show that lysosomal protease deficiency or substrate overload induces lysosomal stress leading to activation of a STAT3-dependent, TFEB-independent pathway of lysosomal hydrolase expression

Functional imaging of legumain in cancer using a new quenched activity-based probe

Item does not contain fulltextLegumain is a lysosomal cysteine protease whose biological function remains poorly defined. Legumain activity is up-regulated in most human cancers and inflammatory diseases most likely as the result of high expression in populations of activated macrophages. Within the tumor microenvironment, legumain activity is thought to promote tumorigenesis. To obtain a greater understanding of the role of legumain activity during cancer progression and inflammation, we developed an activity-based probe that becomes fluorescent only upon binding active legumain. This probe is highly selective for legumain, even in the context of whole cells and tissues, and is also a more effective label of legumain than previously reported probes. Here we present the synthesis and application of our probe to the analysis of legumain activity in primary macrophages and in two mouse models of cancer. We find that legumain activity is highly correlated with macrophage activation and furthermore that it is an ideal marker for primary tumor inflammation and early stage metastatic lesions

Nuclear Legumain Activity in Colorectal Cancer

The cysteine protease legumain is involved in several biological and pathological processes, and the protease has been found over-expressed and associated with an invasive and metastatic phenotype in a number of solid tumors. Consequently, legumain has been proposed as a prognostic marker for certain cancers, and a potential therapeutic target. Nevertheless, details on how legumain advances malignant progression along with regulation of its proteolytic activity are unclear. In the present work, legumain expression was examined in colorectal cancer cell lines. Substantial differences in amounts of pro- and active legumain forms, along with distinct intracellular distribution patterns, were observed in HCT116 and SW620 cells and corresponding subcutaneous xenografts. Legumain is thought to be located and processed towards its active form primarily in the endo-lysosomes; however, the subcellular distribution remains largely unexplored. By analyzing subcellular fractions, a proteolytically active form of legumain was found in the nucleus of both cell lines, in addition to the canonical endo-lysosomal residency. In situ analyses of legumain expression and activity confirmed the endo-lysosomal and nuclear localizations in cultured cells and, importantly, also in sections from xenografts and biopsies from colorectal cancer patients. In the HCT116 and SW620 cell lines nuclear legumain was found to make up approximately 13% and 17% of the total legumain, respectively. In similarity with previous studies on nuclear variants of related cysteine proteases, legumain was shown to process histone H3.1. The discovery of nuclear localized legumain launches an entirely novel arena of legumain biology and functions in cancer