Manuel S Rodriguez

Regulating proteaphagy, a yinyang master mechanism to restore sensitivity to the proteasome inhibitor bortezomib in Mantle Cell Lymphoma cells

Manuel S Rodriguez

LCC-CNRS, Toulouse, France

invited by Naïma Belgareh-Touzé

Friday 14 march 2025, at 11 am at Library

Previous studies using ubiquitin traps combined with mass spectrometry revealed that in Bortezomib (BTZ) resistant Mantle Cell Lymphoma (MCL) cells, a selective autophagy mechanism, known as proteaphagy, was a main mechanism eliminating the proteasome and reducing the sensitivity to this treatment (1). In order to recover the sensitivity to BTZ we have tackled two main molecules that were found enriched in the ubiquitin proteome of those cells, the autophagy receptor p62 and the Tripartite Motif Containing protein 24 (TRIM24) ubiquitin ligase. To investigate how TRIM24 could contribute to this proteolytic crosstalk,  dTRIM24, a proteolysis-targeting chimera (PROTAC), was employed.  dTRIM24 treatment enhanced apoptosis in BTZ-resistant ZBR cells, but no significant difference was observed compared to the parental, BTZ-sensitive Z138 cells. However, the dTRIM24/BTZ combination significantly enhances cooperativity and drives an efficient apoptosis in ZBR cells. The use of a ZBR^{TRIM24 KO} cell line further confirmed the important role of TRIM24 in the triggering of cell death in the context of BTZ resistance. Reducing the TRIM24 protein level in ZBR cells by dTRIM24 or in the context of the ZBR^{TRIM24 KO} cell line allowed the recovery of proteasome activity and explained the apoptosis efficacy observed with the dTRIM24/BTZ treatment. Interestingly, proteaphagy is not significantly affected in the ZBR^{TRIM24 KO} compared to the parental ZBR cell line, indicating that TRIM24 does not directly regulate proteaphagy.  Instead, dTRIM24 treatment resulted in the remodeling of protein ubiquitination favoring the accumulation of K48 Ub chains and their interaction with proteasome subunits. A similar PROTAC strategy was used to tackle p62 and advances on this approach will be presented. Altogether, our data indicate that TRIM24 and p62 play an important role as a regulators of UPS/ALS crosstalk by distinct mechanisms, either by regulating the abundance of K63 vs K48 chains or directly blocking proteaphagy. Understanding the key molecular mechanisms underlying this process is crucial for the development of new combination therapies with the ability to overcome BTZ refractoriness or in general regulating selective autophagy events in distinct pathologies.

References

1. Quinet et al, Cancers (2022) Feb 12;14(4):923. doi: 10.3390/cancers14040923.