Connexin 31.1 degradation requires the Clathrin-mediated autophagy in NSCLC cell H1299

Area of Science:

• Cell Biology
• Cancer Research
• Protein Degradation

Background:

• Connexins, including Connexin 31.1 (Cx31.1), have short half-lives and Cx31.1 is downregulated in non-small cell lung cancer (NSCLC), suggesting tumor-suppressive roles.
• Mechanisms regulating Cx31.1 protein levels remain largely unknown.
• Understanding Cx31.1 regulation is crucial for its potential therapeutic applications in NSCLC.

Purpose of the Study:

• To investigate the cellular mechanisms responsible for the degradation of Connexin 31.1 (Cx31.1).
• To explore the roles of the ubiquitin-proteasome system (UPS) and autophagy in Cx31.1 turnover.
• To identify potential protein interactions involved in Cx31.1 regulation, particularly concerning autophagy.

Main Methods:

• Utilized proteasome inhibitor MG-132 to assess UPS involvement in Cx31.1 degradation.
• Induced autophagy via starvation and Brefeldin A treatment in H1299 cells stably expressing Cx31.1.
• Employed knockdown of autophagy-related protein ATG5 and clathrin using siRNA.
• Performed immunofluorescence analysis for colocalization studies (Cx31.1 and LC3).
• Conducted co-immunoprecipitation assays to investigate protein interactions.

Main Results:

• Inhibition of the ubiquitin-proteasome system (UPS) partially increased Cx31.1 levels, indicating involvement but not complete blockage of degradation.
• Autophagy induction led to decreased Cx31.1 levels, and ATG5 knockdown increased Cx31.1 levels under normal and starvation conditions.
• Cx31.1 colocalized with LC3, and interaction with clathrin heavy chain was observed; clathrin knockdown significantly increased Cx31.1 levels and impaired autophagic lysosome reformation (ALR).

Conclusions:

• Autophagy significantly contributes to the degradation of Connexin 31.1 (Cx31.1).
• Clathrin heavy chain plays a role in regulating Cx31.1 autophagic degradation, potentially through its influence on autophagic lysosome reformation (ALR).
• These findings elucidate novel regulatory pathways for Cx31.1, relevant to its function in cancer.