Endocrine Abstracts

SUMOylation is a post-translational protein modification involved in the regulation of essential cell functions. Our group found several SUMO-1 and SUMO-2/3ylated proteins in human ejaculated spermatozoa (Marchiani et al. 2011). We showed that SUMO-1 is mainly present in live spermatozoa and the percentage of SUMOylated spermatozoa was inversely correlated with total and progressive motility. SUMOylated proteins are mainly located in the nucleus and in the midpiece. To better understand the role of SUMO modification in sperm we aimed to characterize possible target proteins. In particular, we evaluated RanGap-1 (Ran GTPase-activating protein 1) one of the main target of SUMO in somatic cells, DRP1 (Dynamin-related protein 1), whose SUMOylation in somatic cells provokes alterations of mitochondrial functions, and Topoisomerase II alpha, necessary for chromatin condensation and demonstrated to be a target of SUMOylation in germ cells.

By co-immunoprecipitation both with anti-SUMO-1 and with anti-RanGap-1 antibodies, we demonstrated that RanGap-1 is SUMO-1ylated in human sperm. With the same strategy, we showed that DRP-1 is SUMO-1ylated and that the SUMO modified protein is found at higher levels in sperm pools from asthenospermic men respect to normospermic. By confocal microscopy, we observed that the co-localization between SUMO-1 and RanGap-1 and between SUMO-1 and DRP1 are mainly found in the neck area. In addition, we also demonstrated the co-localization between SUMO-1 and Topoisomerase II in the sperm nucleus.

In conclusion, we idenfied RanGap-1, DRP-1 and Topoisomerase II as SUMOylation targets in human sperm. Our data suggest that SUMOylation could play different roles in human sperm functions and the characterization of target proteins is fundamental to reveal such roles. The higher levels of SUMOylated DRP1 in asthenospermic subjects, suggests that alterations in mitochondrial function due to SUMO-modified DRP1 may result in decreased sperm motility whereas sumoylation of RanGap may play a role in silencing gene translation.