Intersectin-1s: a novel nucleo-cytoplasmic endocytic protein

A growing number of proteins involved in endocytosis are reported to undergo nucleocytoplasmic trafficking and interact with different nuclear factors. This mechanism, known as protein moonlighting, is emerging as a key factor in many biological processes, though little is known about the correlation between endocytosis and nuclear functions. Here we investigated the nuclear location of the multi-domain scaffold endocytic protein intersectin-1s, a protein involved in clathrin mediated endocytosis, cell signalling and actin cytoskeleton rearrangements. We detected different Nuclear Localization Signals (NLS) by bioinformatic analysis of the protein sequence. Indeed, by immunofluorescence and biochemical nuclei isolation we revealed the presence of intersectin-1s in the nuclear compartment. Moreover, the protein accumulates in the nucleus under nuclear export inhibition treatment with Leptomycin B. Canonical Nuclear Exporting Signals (NES) were not detected in our protein sequence analysis, thus we searched for potential SUMOylation sites, since many proteins undergoing nucleocytoplasmic trafficking are modified and regulated by this mechanism. Six potential high probability SUMO sites have been found. Elimination of the potential VKGE site at position 769 resulted in a major redistribution of the protein in the nucleus, indicating the involvement of SUMOylation in the nuclear exit of intersectin-1s. In conclusion, our results show for the first time the existence of a nuclear pool of intersectin-1s, which shuttles between nucleus and cytosol and is regulated by SUMOylation.