SERPINB3 (SCCA1) inhibits cathepsin L and lysoptosis, protecting cervical cancer cells from chemoradiation

The endogenous lysosomal cysteine protease inhibitor SERPINB3 (squamous cell carcinoma antigen 1, SCCA1) is elevated in patients with cervical cancer and other malignancies. High serum SERPINB3 is prognostic for recurrence and death following chemoradiation therapy. Cervical cancer cells genetically lacking SERPINB3 are more sensitive to ionizing radiation (IR), suggesting this protease inhibitor plays a role in therapeutic response. Here we demonstrate that SERPINB3-deficient cells have enhanced sensitivity to IR-induced cell death. Knock out of SERPINB3 sensitizes cells to a greater extent than cisplatin, the current standard of care. IR in SERPINB3 deficient cervical carcinoma cells induces predominantly necrotic cell death, with biochemical and cellular features of lysoptosis. Rescue with wild-type SERPINB3 or a reactive site loop mutant indicates that protease inhibitory activity is required to protect cervical tumor cells from radiation-induced death. Transcriptomics analysis of primary cervix tumor samples and genetic knock out demonstrates a role for the lysosomal protease cathepsin L in radiation-induced cell death in SERPINB3 knock-out cells. These data support targeting of SERPINB3 and lysoptosis to treat radioresistant cervical cancers.

Helicobacter pylori and gastric cancer: a lysosomal protease perspective

The intimate involvement of pathogens with the heightened risk for developing certain cancers is an area of research that has captured a great deal of attention over the last 10 years. One firmly established paradigm that highlights this aspect of disease progression is in the instance of Helicobacter pylori infection and the contribution it makes in elevating the risk for developing gastric cancer. Whilst the molecular mechanisms that pinpoint the contribution that this microorganism inflicts towards host cells during gastric cancer initiation have come into greater focus, another picture that has also emerged is one that implicates the host’s immune system, and the chronic inflammation that can arise therefrom, as being a central contributory factor in disease progression. Consequently, when taken with the underlying role that the extracellular matrix plays in the development of most cancers, and how this dynamic can be modulated by proteases expressed from the tumor or inflammatory cells, a complex and detailed relationship shared between the individual cellular components and their surroundings is coming into focus. In this review article, we draw attention to the emerging role played by the cathepsin proteases in modulating the stage-specific progression of Helicobacter pylori-initiated gastric cancer and the underlying immune response, while highlighting the therapeutic significance of this dynamic and how it may be amenable for novel intervention strategies within a basic research or clinical setting.

TMPRSS2 promotes SARS-CoV-2 evasion from NCOA7-mediated restriction

Interferons play a critical role in regulating host immune responses to SARS-CoV-2, but the interferon (IFN)-stimulated gene (ISG) effectors that inhibit SARS-CoV-2 are not well characterized. The IFN-inducible short isoform of human nuclear receptor coactivator 7 (NCOA7) inhibits endocytic virus entry, interacts with the vacuolar ATPase, and promotes endo-lysosomal vesicle acidification and lysosomal protease activity. Here, we used ectopic expression and gene knockout to demonstrate that NCOA7 inhibits infection by SARS-CoV-2 as well as by lentivirus particles pseudotyped with SARS-CoV-2 Spike in lung epithelial cells. Infection with the highly pathogenic, SARS-CoV-1 and MERS-CoV, or seasonal, HCoV-229E and HCoV-NL63, coronavirus Spike-pseudotyped viruses was also inhibited by NCOA7. Importantly, either overexpression of TMPRSS2, which promotes plasma membrane fusion versus endosomal fusion of SARS-CoV-2, or removal of Spike’s polybasic furin cleavage site rendered SARS-CoV-2 less sensitive to NCOA7 restriction. Collectively, our data indicate that furin cleavage sensitizes SARS-CoV-2 Spike to the antiviral consequences of endosomal acidification by NCOA7, and suggest that the acquisition of furin cleavage may have favoured the co-option of cell surface TMPRSS proteases as a strategy to evade the suppressive effects of IFN-induced endo-lysosomal dysregulation on virus infection.

Ca2+ administration prevents α-synuclein proteotoxicity by stimulating calcineurin-dependent lysosomal proteolysis

The capacity of a cell to maintain proteostasis progressively declines during aging. Virtually all age-associated neurodegenerative disorders associated with aggregation of neurotoxic proteins are linked to defects in the cellular proteostasis network, including insufficient lysosomal hydrolysis. Here, we report that proteotoxicity in yeast and Drosophila models for Parkinson’s disease can be prevented by increasing the bioavailability of Ca2+, which adjusts intracellular Ca2+ handling and boosts lysosomal proteolysis. Heterologous expression of human α-synuclein (αSyn), a protein critically linked to Parkinson’s disease, selectively increases total cellular Ca2+ content, while the levels of manganese and iron remain unchanged. Disrupted Ca2+ homeostasis results in inhibition of the lysosomal protease cathepsin D and triggers premature cellular and organismal death. External administration of Ca2+ reduces αSyn oligomerization, stimulates cathepsin D activity and in consequence restores survival, which critically depends on the Ca2+/calmodulin-dependent phosphatase calcineurin. In flies, increasing the availability of Ca2+ discloses a neuroprotective role of αSyn upon manganese overload. In sum, we establish a molecular interplay between cathepsin D and calcineurin that can be activated by Ca2+ administration to counteract αSyn proteotoxicity.

Enterococcus faecalis persists and replicates within epithelial cells in vitro and in vivo during wound infection

Enterococcus faecalis is a frequent opportunistic pathogen of wounds, whose infections are associated with biofilm formation, persistence, and recalcitrance toward treatment. We have previously shown that E. faecalis wound infection persists for at least 7 days. Here we report that viable E. faecalis are present within both immune and non-immune cells at the wound site up to 5 days after infection, raising the prospect that intracellular persistence contributes to chronic E. faecalis infection. Using an in vitro keratinocyte infection model, we show that a subpopulation of E. faecalis becomes internalized via macropinocytosis into single membrane-bound compartments, where they can survive and replicate. These intracellular E. faecalis can persist in late endosomes up to 72 hours after infection in the absence of colocalization with the lysosomal protease cathepsin D or apparent fusion with the lysosome, suggesting that E. faecalis blocks endosomal maturation. Indeed, intracellular E. faecalis infection results in a marked reduction in Rab7 expression, a small GTPase required for endosome-lysosome fusion. Finally, we demonstrate that intracellular E. faecalis derived from infected keratinocytes are significantly more efficient in reinfecting new keratinocytes. Together, these data suggest that intracellular proliferation of E. faecalis may contribute to its persistence in the face of a robust immune response, providing a primed reservoir of bacteria for subsequent reinfection.

Prognostic Significance and Oncogene Function of Cathepsin A in Hepatocellular Carcinoma

Cathepsin A (CTSA) is a lysosomal protease that regulates galactoside metabolism. The previous study has shown CTSA is abnormally expressed in various types of cancer. However, rarely the previous study has addressed the role of CTSA in hepatocellular carcinoma (HCC) and its prognostic value. To study the clinical value and potential function of CTSA in HCC, datasets from the Cancer Genome Atlas (TCGA) database and a 136 HCC patient cohort were analyzed. CTSA expression was found to be significantly higher in HCC patients compared with normal liver tissues, which was supported by immunohistochemistry (IHC) validation. Both gene ontology (GO) and The Kyoto Encyclopedia of Genes and Genomes (KEGG) analyses demonstrated that CTSA co-expressed genes were involved in ATP hydrolysis coupled proton transport, carbohydrate metabolic process, lysosome organization, oxidative phosphorylation, other glycan degradation, etc. Survival analysis showed a significant reduction both in overall survival (OS) and recurrence-free survival (RFS) of patients with high CTSA expression from both the TCGA HCC cohort and 136 patients with the HCC cohort. Furthermore, CTSA overexpression has diagnostic value in distinguishing between HCC and normal liver tissue (Area under curve (AUC) = 0.864). Moreover, Gene set enrichment analysis (GSEA) showed that CTSA expression correlated with the oxidative phosphorylation, proteasome, and lysosome, etc. in HCC tissues. These findings demonstrate that CTSA may as a potential diagnostic and prognostic biomarker in HCC.

Cathepsin L, a Target of Hypoxia-Inducible Factor-1-α, Is Involved in Melanosome Degradation in Melanocytes

Hypoxic conditions induce the activation of hypoxia-inducible factor-1α (HIF-1α) to restore the supply of oxygen to tissues and cells. Activated HIF-1α translocates into the nucleus and binds to hypoxia response elements to promote the transcription of target genes. Cathepsin L (CTSL) is a lysosomal protease that degrades cellular proteins via the endolysosomal pathway. In this study, we attempted to determine if CTSL is a hypoxia responsive target gene of HIF-1α, and decipher its role in melanocytes in association with the autophagic pathway. The results of our luciferase reporter assay showed that the expression of CTSL is transcriptionally activated through the binding of HIF1-α at its promoter. Under autophagy-inducing starvation conditions, HIF-1α and CTSL expression is highly upregulated in melan-a cells. The mature form of CTSL is closely involved in melanosome degradation through lysosomal activity upon autophagosome–lysosome fusion. The inhibition of conversion of pro-CTSL to mature CTSL leads to the accumulation of gp100 and tyrosinase in addition to microtubule-associated protein 1 light chain 3 (LC3) II, due to decreased lysosomal activity in the autophagic pathway. In conclusion, we have identified that CTSL, a novel target of HIF-1α, participates in melanosome degradation in melanocytes through lysosomal activity during autophagosome–lysosome fusion.

Cleavage of histone H2A during embryonic stem cell differentiation destabilizes nucleosomes to counteract gene activation

Histone proteolysis is a poorly understood phenomenon in which the N-terminal tails of histones are irreversibly cleaved by intracellular proteases. During development, histone post-translational modifications are known to orchestrate gene expression patterns that ultimately drive cell fate decisions. Therefore, deciphering the mechanisms of histone proteolysis is necessary to enhance the understanding of cellular differentiation. Here we show that H2A is cleaved by the lysosomal protease Cathepsin L during ESCs differentiation. Using quantitative mass spectrometry (MS), we identified L23 to be the primary cleavage site that gives rise to the clipped form of H2A (cH2A), which reaches a maximum level of ~1% of total H2A after four days of differentiation. Using ChIP-seq, we found that preventing proteolysis leads to an increase in acetylated H2A at promoter regions in differentiated ES cells. We also report the identification of novel readers of acetylated H2A in pluripotent ES cells, including members of the PBAF remodeling complex, which can recognize different acetylated forms of H2A. Finally, we show that H2A proteolysis abolishes this recognition. Altogether, our data suggests that proteolysis serves as an efficient mechanism to silence pluripotency genes and destabilize the nucleosome core particle.

TMPRSS2 promotes SARS-CoV-2 evasion from NCOA7-mediated restriction

Interferons play a critical role in regulating host immune responses to SARS-CoV-2, but the interferon (IFN)-stimulated gene (ISG) effectors that inhibit SARS-CoV-2 are not well characterized. The IFN-inducible short isoform of human nuclear receptor coactivator 7 (NCOA7) inhibits endocytic virus entry, interacts with the vacuolar ATPase, and promotes endo-lysosomal vesicle acidification and lysosomal protease activity. Here, we used ectopic expression and gene knockout to demonstrate that NCOA7 inhibits infection by SARS-CoV-2 as well as by lentivirus particles pseudotyped with SARS-CoV-2 Spike in lung epithelial cells. Infection with the highly pathogenic, SARS-CoV-1 and MERS-CoV, or seasonal, HCoV-229E and HCoV-NL63, coronavirus Spike-pseudotyped viruses was also inhibited by NCOA7. Importantly, either overexpression of TMPRSS2, which promotes plasma membrane fusion versus endosomal fusion of SARS-CoV-2, or removal of Spike’s polybasic furin cleavage site rendered SARS-CoV-2 less sensitive to NCOA7 restriction. Collectively, our data indicate that furin cleavage sensitizes SARS-CoV-2 Spike to the antiviral consequences of endosomal acidification by NCOA7, and suggest that the acquisition of furin cleavage may have favoured the co-option of cell surface TMPRSS proteases as a strategy to evade the suppressive effects of IFN-induced endo-lysosomal dysregulation on virus infection.

Prognostic significance and oncogene function of cathepsin A in hepatocellular carcinoma

Cathepsin A (CTSA) is a lysosomal protease that regulates galactoside metabolism. The previous study has shown CTSA is abnormally expressed in various types of cancer. However, rarely the previous study has addressed the role of CTSA in hepatocellular carcinoma (HCC) and its prognostic value. To study the clinical value and potential function of CTSA in HCC, datasets from the Cancer Genome Atlas (TCGA) database and a 136 HCC patient cohort were analyzed. CTSA expression was found to be significantly higher in HCC patients compared with normal liver tissues, which was supported by immunohistochemistry (IHC) validation. Both gene ontology (GO) and The Kyoto Encyclopedia of Genes and Genomes (KEGG) analyses demonstrated that CTSA co-expressed genes were involved in ATP hydrolysis coupled proton transport, carbohydrate metabolic process, lysosome organization, oxidative phosphorylation, other glycan degradation, etc. Survival analysis showed a significant reduction both in overall survival (OS) and recurrence-free survival (RFS) of patients with high CTSA expression from both the TCGA HCC cohort and 136 patients with the HCC cohort. Furthermore, CTSA overexpression has diagnostic value in distinguishing between HCC and normal liver tissue [Area under curve (AUC) = 0.864]. Moreover, Gene set enrichment analysis (GSEA) showed that CTSA expression correlated with the oxidative phosphorylation, proteasome, and lysosome, etc. in HCC tissues. These findings demonstrate that CTSA may as a potential diagnostic and prognostic biomarker in HCC.