Reorientation of the SUMOylation landscape and altered L3mbtl2-mediated transcriptional activity in cancer-associated muscle contractile dysfunction.

Cachexia is a debilitating muscle-wasting disorder associated with a high mortality rate in cancer patients. However, the molecular mechanisms of muscle contractile dysfunction underlying cancer-induced cachexia (CIC) remain poorly characterized. Here, we demonstrated that CIC reorients global SUMOylation in skeletal muscle cells and alters the stability of various SUMO machinery components, particularly SUMO isopeptidases. The non-canonical polycomb repressor protein L3mbtl2 was among the predominant proteins with enhanced SUMOylation level in CIC. Surprisingly, in contrast to previous notions, we found that L3mbtl2 activates transcription of a large cohort of genes regulating muscle contraction. Mechanistically, L3mbtl2 associates with Ash2L, a component of the SET1/MLL histone methyltransferase complex. Increased SUMO modification of L3mbtl2 in CIC leads to partitioning of Ash2L from its target genes, resulting in impaired calcium handling, sarcomere disorganization and impeded muscle cell contractile properties. Our findings reveal an unprecedented connection between SUMO and CIC, a paradoxical SUMO-associated transcriptional activator function of L3MBTL2 and hold potential for developing therapeutic interventions to ameliorate CIC.