Impaired turnover of autophagolysosomes in cathepsin L deficiency

Abstract

Some of the phenotypes of mice deficient for the lysosomal cysteine endopeptidase cathepsin L (Ctsl) are characterized by large dysmorphic vesicles in the cytoplasm. Specifically, the heart (dilative cardiomyopathy), the thyroid (impaired thyroglobulin processing) and keratinocytes (periodic hair loss and epidermal hyperproliferation) are affected. We hypothesized that the formation of aberrant vesicles is owing to defects in macroautophagy. Therefore, primary mouse embryonic fibroblasts (MEF), which were derived from Ctsl(-/-) animals crossed with mice transgenic for the autophagy marker GFP-LC3, were investigated. Ctsl(-/-) MEF show increased number and size of vesicular structures belonging to the 'acidic' cellular compartment and are also characterized by GFP-LC3. Induction of autophagy by nutrient starvation or rapamycin treatment showed no significant impairment of the initiation of autophagy, the formation of autophagosomes or autophagosome-lysosome fusion in Ctsl(-/-) MEF, but co-localization of GFP-LC3 and Lamp1 revealed unusually large autophagolysosomes filled with Lamp1. Furthermore, the soluble lysosomal enzyme cathepsin D was elevated in Ctsl(-/-) MEF. Thus, degradation of autophagolysosomal content is impaired in the absence of Ctsl. This could slow the turnover of autophagolysosomes and result in accumulation of the dysmorphic and 'acidic' vesicles that were previously described in the context of the pathological phenotypes of Ctsl(-/-) mice.

Out-of-frame start codons prevent translation of truncated nucleo-cytosolic cathepsin L in vivo

“…Similar vesicular accumulations have already been found in MEFs, keratinocytes and cardiomyocytes of Ctsl À / À mice 11,15,45,46 . Most likely these vesicular accumulations represent a variation of classical storage disorders triggered by impaired lysosomal degradation 47 .…”

“…MEFs were prepared as described previously 45 . Briefly, embryos of the genotypes wild type, Ctsl À / À and Ctsb À / À Ctsl À / À were killed at embryonic day 12.5.…”

Stress-resistant Translation of Cathepsin L mRNA in Breast Cancer Progression

“…Inhibition of mTOR is a common tool to induce autophagy in cells. The advantage of CTSL mRNA translation under such conditions might mirror its functional role in autophagy as it is needed for the turnover of autophagolysosomes (39).…”

Specialized roles for cysteine cathepsins in health and disease

“…Cathepsin L-deficient mouse keratinocytes show enhanced recycling of nondegraded plasma membrane receptors and their ligands to the cell surface and sustained growth factor signaling (72). This impaired termination of growth factor signaling within the endolysosomal compartment results in increased Ras, Akt, and MAPK activation (73). As a consequence, the proliferation of basal epidermal keratinocytes is increased.…”