Link to bioRxiv paper:
http://biorxiv.org/cgi/content/short/2023.02.13.528037v1?rss=1

Authors: Renna, F. J., Steinberg, J. H. E., Manifava, M., Gonzalez, C. D., Tadic, M. S., Orquera, T., Vecino, C. V., Ropolo, A., Rossi, M., Ktistakis, N. T., Vaccaro, M. I.

Abstract:
Autophagy is a tightly regulated catabolic process involved in the degradation and recycling of proteins and organelles. Ubiquitination plays an important role in the regulation of autophagy. VMP1 is an essential autophagy protein whose expression in pancreatic cancer stem cells, carrying activated KRAS, triggers autophagy and enables therapy resistance. Using biochemical and cellular approaches we investigated VMP1 ubiquitination in the autophagic process of human tumor cells. We identified ubiquitination as a post-translational modification for VMP1. VMP1 is ubiquitinated early in autophagosome biogenesis and remains ubiquitinated as part of the autophagosome membrane throughout autophagic flux until autolysosome formation. However, VMP1 is not degraded by autophagy nor by the ubiquitin-proteasomal system. Mass spectrometry and immunoprecipitation showed that Cdt2, the substrate recognition subunit of the E3 ligase complex associated with cancer CRL4, is a novel interactor of VMP1. Cdt2 is involved in the VMP1 ubiquitination since Cdt2 relocates from the nucleus to the perinuclear region under VMP1 expression. Moreover, VMP1 ubiquitination decreases under the CRL inhibitor MLN4924 and increases with the Cdt2 overexpression. Our results indicate that ubiquitination is a novel post-translational modification of VMP1 in autophagy human tumor cells. VMP1 ubiquitination would be of clinical relevance in tumor cell therapy resistance.

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