ABSTRACT
Arsenic is an effective treatment for Acute Promyelocytic Leukaemia as it induces degradation of the Promyelocytic Leukaemia (PML) – retinoic acid receptor alpha (RARA) oncogenic fusion protein. Some patients relapse with arsenic resistant disease because of missense mutations in PML. To determine the mechanistic basis for this arsenic resistance we reconstituted PML-/- cells with wild type (WT) and two mutant forms of YFP-PMLV found in patients refractory to arsenic, A216T and L217F. Both mutants formed PML bodies that were larger, but less numerous than WT and neither responded to arsenic by degradation. Analysis of immunoprecipitated PML bodies indicated that while WT PML experiences increased SUMO1, SUMO2/3 and ubiquitin conjugation, A216T PML is almost completely unresponsive and does not recruit the SUMO targeted ubiquitin E3 ligase RNF4. L217F PML was modified by SUMO and recruited RNF4, but failed to develop the the type of ubiquitin conjugate required to recruit the segregase p97, which is essential for PML degradation. Thus, the two PML mutants fail to be degraded as they do not acquire the necessary SUMO and ubiquitin signals required to progress through the degradation pathway.
Competing Interest Statement
The authors have declared no competing interest.
