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Updated: May 12, 2026
Evaluation of Substrate Ubiquitylation by E3 Ubiquitin-ligase in Mammalian Cell Lysates
Published on: May 10, 2022
UVA causes dual inactivation of cathepsin B and L underlying lysosomal dysfunction in human dermal fibroblasts
Sarah D Lamore1, Georg T Wondrak
1Department of Pharmacology and Toxicology, College of Pharmacy & Arizona Cancer Center, University of Arizona, Tucson, AZ 85724, USA.
Abstract:
Cutaneous exposure to chronic solar UVA-radiation is a causative factor in photocarcinogenesis and photoaging. Recently, we have identified the thiol-dependent cysteine-protease cathepsin B as a novel UVA-target undergoing photo-oxidative inactivation upstream of autophagic-lysosomal dysfunction in fibroblasts. In this study, we examined UVA effects on a wider range of cathepsins and explored the occurrence of UVA-induced cathepsin inactivation in other cultured skin cell types. In dermal fibroblasts, chronic exposure to non-cytotoxic doses of UVA caused pronounced inactivation of the lysosomal cysteine-proteases cathepsin B and L, effects not observed in primary keratinocytes and occurring only to a minor extent in primary melanocytes. In order to determine if UVA-induced lysosomal impairment requires single or dual inactivation of cathepsin B and/or L, we used a genetic approach (siRNA) to selectively downregulate enzymatic activity of these target cathepsins. Monitoring an established set of protein markers (including LAMP1, LC3-II, and p62) and cell ultrastructural changes detected by electron microscopy, we observed that only dual genetic antagonism (targeting both CTSB and CTSL expression) could mimic UVA-induced autophagic-lysosomal alterations, whereas single knockdown (targeting CTSB or CTSL only) did not display 'UVA-mimetic' effects failing to reproduce the UVA-induced phenotype. Taken together, our data demonstrate that chronic UVA inhibits both cathepsin B and L enzymatic activity and that dual inactivation of both enzymes is a causative factor underlying UVA-induced impairment of lysosomal function in dermal fibroblasts.
Insights
Chronic UVA radiation inactivates cathepsin B and L enzymes in skin fibroblasts, leading to impaired lysosomal function. Dual inactivation of both cathepsins is necessary to mimic UVA
Area of Science:
- Dermatology
- Cell Biology
- Biochemistry
Background:
- Chronic UVA radiation causes skin damage, including photoaging and photocarcinogenesis.
- Cathepsin B, a cysteine-protease, was previously identified as a UVA target involved in autophagic-lysosomal dysfunction.
- The specific roles of cathepsins in UVA-induced skin damage require further elucidation.
Purpose of the Study:
- To investigate the effects of UVA radiation on a broader spectrum of cathepsins in various skin cell types.
- To determine whether UVA-induced lysosomal impairment necessitates the inactivation of single or multiple cathepsins.
- To explore the mechanism underlying UVA-induced autophagic-lysosomal dysfunction in dermal fibroblasts.
Main Methods:
- Exposure of cultured dermal fibroblasts, keratinocytes, and melanocytes to chronic UVA radiation.
- Assessment of cathepsin B and L enzymatic activity following UVA exposure.
- Genetic downregulation of cathepsin B (CTSB) and cathepsin L (CTSL) expression using siRNA.
- Monitoring of autophagic-lysosomal markers (LAMP1, LC3-II, p62) and cellular ultrastructure via electron microscopy.
Main Results:
- Chronic UVA exposure inactivated cathepsin B and L in dermal fibroblasts, with minimal effects in keratinocytes and melanocytes.
- Single genetic knockdown of CTSB or CTSL did not replicate UVA-induced autophagic-lysosomal alterations.
- Dual genetic downregulation of both CTSB and CTSL successfully mimicked the UVA-induced phenotype, including lysosomal dysfunction.
- UVA-induced lysosomal impairment in fibroblasts was associated with the dual inactivation of cathepsin B and L.
Conclusions:
- Chronic UVA radiation inhibits the enzymatic activity of both cathepsin B and L in dermal fibroblasts.
- The dual inactivation of cathepsin B and L is a key causative factor in UVA-induced autophagic-lysosomal dysfunction.
- These findings provide novel insights into the molecular mechanisms of UVA-induced skin damage and potential therapeutic targets.
