A novel nonsense mutation in cathepsin C gene in an Egyptian patient presenting with Papillon–Lefèvre syndrome

Abnormal profiles of cathepsin C secreted in urine of Papillon Lefevre syndrome patients

BACKGROUND

Papillon Lefevre syndrome (PLS) is an autosomal recessive disorder that results from a mutated gene that encodes a lysosomal peptidase known as cathepsin C (CTSC). The clinical presentation of PLS involves mainly palmoplantar keratosis and periodontitis with a variable degree of severity.

SUBJECTS

and methods: Our study included ten patients with a broad spectrum of palmoplantar keratosis and periodontitis severity. CTSC variants were detected by Sanger sequencing. CTSC protein secreted in urine was detected by western blotting.

RESULTS

Five patients have missense variants, Four have nonsense variants, and one has splice variants in CTSC. The activation products of cathepsin C protein (Heavy and light chains) were absent in all patients' urine samples except one with a significantly reduced level compared to the controls. The dimeric form of CTSC protein was found in all the studied cases. The monomeric form was found in five cases. The products of proteolytic activation of CTSC by other cathepsins (L and S) were found in the urine samples of five of the patients. Each patient had a characteristic pattern of accumulated CTSC protein maturation/activation substrates, intermediates, and products. 40% of the patients had the activation products of other lysosomal cathepsins.

CONCLUSION

Urinary CTSC in PLS patients could be used as a diagnostic biomarker for the biochemical screening of the disease. Different variants in CTSC result in different profiles of CTSC secreted in the urine of PLS patients. The profiles of secreted CTSC in urine could be correlated to the severity of palmoplantar keratosis.

Consequences of cathepsin C inactivation for membrane exposure of proteinase 3, the target antigen in autoimmune vasculitis

Membrane-bound proteinase 3 (PR3^m) is the main target antigen of anti-neutrophil cytoplasmic autoantibodies (ANCA) in granulomatosis with polyangiitis, a systemic small-vessel vasculitis. Binding of ANCA to PR3^m triggers neutrophil activation with the secretion of enzymatically active PR3 and related neutrophil serine proteases, thereby contributing to vascular damage. PR3 and related proteases are activated from pro-forms by the lysosomal cysteine protease cathepsin C (CatC) during neutrophil maturation. We hypothesized that pharmacological inhibition of CatC provides an effective measure to reduce PR3^m and therefore has implications as a novel therapeutic approach in granulomatosis with polyangiitis. We first studied neutrophilic PR3 from 24 patients with Papillon-Lefèvre syndrome (PLS), a genetic form of CatC deficiency. PLS neutrophil lysates showed a largely reduced but still detectable (0.5-4%) PR3 activity when compared with healthy control cells. Despite extremely low levels of cellular PR3, the amount of constitutive PR3^m expressed on the surface of quiescent neutrophils and the typical bimodal membrane distribution pattern were similar to what was observed in healthy neutrophils. However, following cell activation, there was no significant increase in the total amount of PR3^m on PLS neutrophils, whereas the total amount of PR3^m on healthy neutrophils was significantly increased. We then explored the effect of pharmacological CatC inhibition on PR3 stability in normal neutrophils using a potent cell-permeable CatC inhibitor and a CD34⁺ hematopoietic stem cell model. Human CD34⁺ hematopoietic stem cells were treated with the inhibitor during neutrophil differentiation over 10 days. We observed strong reductions in PR3^m, cellular PR3 protein, and proteolytic PR3 activity, whereas neutrophil differentiation was not compromised.