Abstract
In contrast to our extensive knowledge on ubiquitin polymer signaling, we are severely limited in our understanding of poly-SUMO signaling. We set out to identify substrates conjugated to SUMO polymers, using knockdown of the poly-SUMO2/3 protease SENP6. We identify over 180 SENP6 regulated proteins that represent highly interconnected functional groups of proteins including the constitutive centromere-associated network (CCAN), the CENP-A loading factors Mis18BP1 and Mis18A and DNA damage response factors. Our results indicate a striking protein group de-modification by SENP6. SENP6 deficient cells are severely compromised for proliferation, accumulate in G2/M and frequently form micronuclei. Accumulation of CENP-T, CENP-W and CENP-A to centromeres is impaired in the absence of SENP6. Surprisingly, the increase of SUMO chains does not lead to ubiquitin-dependent proteasomal degradation of the CCAN subunits. Our results indicate that SUMO polymers can act in a proteolysis-independent manner and consequently, have a more diverse signaling function than previously expected.