Identification of a-Tocopherol succinate as an RFFL-substrate interaction inhibitor inducing peripheral CFTR stabilization and apoptosis

The E3 ubiquitin ligase RFFL is an apoptotic inhibitor highly expressed in cancers and its knockdown suppresses cancer cell growth and sensitizes to chemotherapy. RFFL also participates in peripheral protein quality control which removes the functional cell surface Delta F508-CFTR channel and reduces the efficacy of pharmaceutical therapy for cystic fibrosis (CF). Although RFFL inhibitors have therapeutic potential for both cancer and CF, they remain undiscovered. Here, a chemical array screening has identified a-tocopherol succinate (alpha TOS) as an RFFL ligand. NMR analysis revealed that aTOS directly binds to RFFL's substrate-binding region without affecting the E3 enzymatic activity. Consequently, aTOS inhibits the RFFL-substrate interaction, Delta F508-CFTR ubiquitination and elimination from the plasma membrane of epithelial cells, resulting in the increased functional CFTR channel. Among the a-tocopherol (alpha TOL) analogs we tested, only aTOS inhibited the RFFL-substrate interaction and increased the cell surface Delta F508-CFTR, depending on RFFL expression. Similarly, the unique proapoptotic effect of aTOS was dependent on RFFL expression. Thus, unlike other aTOL analogs, aTOS acts as an RFFL protein-protein interaction inhibitor which may explain its unique biological properties among aTOL analogs. Moreover, aTOS may act as a CFTR stabilizer, a novel class of drugs that extend cell surface Delta F508-CFTR lifetime.

Automated summary

RFFL is a highly expressed apoptotic inhibitor in cancers, and its inhibition suppresses cancer cell growth and enhances chemotherapy sensitivity. It has been discovered that α-tocopherol succinate (alpha TOS) can act as a ligand for RFFL, inhibiting the RFFL-substrate interaction and increasing the cell surface expression of CFTR channel, which may have therapeutic potential for both cancer and cystic fibrosis.