The deubiquitinase Usp27x as a novel regulator of cFLIPL protein expression and sensitizer to death-receptor-induced apoptosis

• Published in: Apoptosis (London) Vol. 27; no. 1-2; pp. 112 - 132
• Main Authors: Dold, Manuel Nico, Ng, Xiulin, Alber, Claudia, Gentle, Ian Edward, Häcker, Georg, Weber, Arnim
• Format: Journal Article
• Language: English
• Published: New York Springer US 01-02-2022; Springer Nature B.V
• Subjects: Apoptosis; Bcl-2 protein; BIM protein; Biochemistry; Biomedical and Life Sciences; Biomedicine; c-FLIP protein; Cancer Research; Caspase-8; Cell Biology; Cell death; Death receptors; Melanoma; Membrane proteins; Mortality; Oncology; Polyinosinic:polycytidylic acid; Proteasomes; Protein expression; Proteins; Receptors; Signal transduction; Signaling; TLR3 protein; Toll-like receptors; Transcription; Tumor necrosis factor; Tumor necrosis factor receptor 1; Tumor necrosis factor-TNF; Ubiquitin; Ubiquitin-protein ligase; Ubiquitin-specific proteinase; Ubiquitination; Virology; Caspase-8; TRIM28; Usp27x; TNF; TLR3; Apoptosis
• ISSN: 1360-8185; 1573-675X
• DOI: 10.1007/s10495-021-01706-9

Death receptors are transmembrane proteins that can induce the activation of caspase-8 upon ligand binding, initiating apoptosis. Recent work has highlighted the great molecular complexity of death receptor signalling, in particular through ubiquitination/deubiquitination. We have earlier defined the deubiquitinase Ubiquitin-Specific Protease 27x (Usp27x) as an enzyme capable of stabilizing the pro-apoptotic Bcl-2 family member Bim. Here, we report that enhanced expression of Usp27x in human melanoma cells leads to the loss of cellular FLICE-like inhibitory protein (cFLIP) and sensitizes to Tumor necrosis factor receptor 1 (TNF-R1) or Toll-like receptor 3 (TLR3)-induced extrinsic apoptosis through enabling enhanced processing of caspase-8. The loss of cFLIP
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upon overexpression of Usp27x was not due to reduced transcription, could be partially counteracted by blocking the ubiquitin proteasome system and was independent of the known cFLIP
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destabilizing ubiquitin E3-ligases Itch and DTX1. Instead, Usp27x interacted with the E3-ligase TRIM28 and reduced ubiquitination of TRIM28. Reduction of cFLIP
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protein levels by Usp27x-induction depended on TRIM28, which was also required for polyI:C-induced cell death. This work defines Usp27x as a novel regulator of cFLIP
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protein expression and a deubiquitinase in fine tuning death receptor signalling pathways to execute apoptosis.