Cajal body formation is regulated by coilin SUMOylation

Cajal bodies (CBs) are membraneless organelles whose mechanism of formation is still not fully understood. Many proteins contribute to the formation of CBs, including Nopp140 (NOLC1), WRAP53 and coilin. Coilin is modified on multiple different lysine residues by SUMO, the small ubiquitin-like modifier. In addition to its accumulation in CBs, coilin is also found in the nucleoplasm, where its role is still being evaluated. Here, we demonstrate a novel mechanism of CB regulation by examining the interaction changes of coilin when its SUMOylation is disrupted. The impact of global SUMOylation inhibition and targeted disruption of coilin SUMOylation on CB formation was examined. We found that two types of global SUMOylation inhibition and expression of SUMO-deficient coilin mutants increased CB number but decreased CB size. Additionally, we saw via coimmunoprecipitation that a SUMO-deficient coilin mutant has altered interaction with Nopp140. This demonstrates increased mechanistic ties between CB formation and SUMOylation.