A potentially therapeutic method to interfere with CSNAP activity, a key negative regulator of protein degradation.
Protein degradation is one of the most essential mechanisms regulating the proteome and its responses to stimuli. The process is largely mediated by E3 ligases, which ubiquitinate target proteins, tagging them for degradation. Cullin-RING ligases (CRLs) comprise one of the largest E3 ligase families, which includes ~250 complexes modularly built around a central cullin scaffold, which is then associated with a specific substrate receptor, adaptor protein and a RING protein that recruits the E2 ubiquitin-conjugating enzyme. The specific set of CRLs active at a given time dictates the dynamics and specificity of protein assembly and disassembly formulating the response to regulatory cues. Given its central role in regulating an array of cellular processes, including cell division and proliferation, it is not surprising that impaired CRL function has been correlated with numerous pathologies, rendering it an attractive therapeutic target.
All CRLs are regulated by the COP9 signalosome complex (CSN), either via enzymatic deconjugation of a ubiquitin-like protein from the cullin subunit (deneddylation) or via steric hindrance of key substrate binding regions, ultimately inhibiting CRL activity. CSN is comprised of eight subunits linked together by CSNAP, a 57-amino acid protein recently discovered by Michal Sharon and her team. The group found that absence of CSNAP compromised the disassembly and assembly of CRL complexes, which led to global proteomic shifts, disrupted cell morphology, growth and cell cycle progression and impaired DNA damage response. Thus, agents attenuating the incorporation of CSNAP into CSN complexes may be potent therapeutics for conditions associated with aberrant protein degradation.
The research team found that meristoylated forms of the C’-terminal peptide of CSNAP were highly cell-permeable and significantly reduced HAP1 cell viability and proliferation in a dose-dependent manner. The peptide competed with and displaced endogenous full-length CSNAP proteins, and successfully incorporated into CSN complexes in HAP1 cells. Further studies demonstrated that substitution of specific amino acids in the unstructured C-terminal tail of C-CSNAP, enhanced CSNAP displacement from CSN.
- Therapeutic candidate for conditions associated with aberrant protein degradation
- Specific modifications of CSNAP uncoupled its steric and catalytic activities, providing a means of targeting specific functional roles of CSN in cellular processes and pathologies.
Present results involve comprehensive in vitro characterization of the C-myristoyl CSNAP peptide, including its cellular effect, conformational structure and interaction with CNS subunits.
