Abstract
SUN2 is an inner nuclear membrane protein with a conserved Sad1/UNC-84 homology SUN-domain at the C-terminus. Intriguingly, SUN2 has also been reported to interact with Rab5, which localizes in early endosomes. To clarify the dual subcellular localization of SUN2, we investigated its localization in lamin A/C deficient cells rescued with lamin A or lamin C isoform, and in HeLa cells transfected with Rab5 or its mutants. We found that expression of lamin A but not lamin C partly restored the nuclear envelope localization of SUN2. SUN2 was redistributed to endosomes upon overexpression of Rab5, but remained on the nuclear envelope when the SUN domain was deleted. To explore the physiological function of SUN2 in vesicle trafficking and endocytosis, we demonstrated the colocalization of endogenous SUN2 and Rab5. Moreover, overexpression of SUN2 stimulated the uptake of transferrin while suppression of SUN2 expression attenuated the process. These findings support a role of SUN2 in endocytosis.
Highlights
SUN2 belongs to a family of proteins with a conserved Cterminal Sad1/UNC-84 homology (SUN) domain
Proteomic screening analyses have revealed that both SUN1 and SUN2 reside on the nuclear envelope (NE) [3,4]
hemagglutinin A (HA)-tagged SUN3 is localized to the NE [5], SPAG4/SUN4 is found in outer dense fiber of sperm tail [6], SPAG4L and SPAG4L2 are NE proteins specific to spermatids [7]
Summary
SUN2 belongs to a family of proteins with a conserved Cterminal Sad1/UNC-84 homology (SUN) domain. UNC-84 is a Caenorhabditis elegans protein which is required for nuclear migration and anchoring during development [1]. The nuclear envelope (NE) localization of UNC-84 depends on Ce-lamin [2]. The SUN domain is present in six reported proteins termed SUN1, SUN2, SUN3, SPAG4/SUN4, SPAG4L/SUN5 and SPAG4L2. Proteomic screening analyses have revealed that both SUN1 and SUN2 reside on the NE [3,4]. HA-tagged SUN3 is localized to the NE [5], SPAG4/SUN4 is found in outer dense fiber of sperm tail [6], SPAG4L and SPAG4L2 are NE proteins specific to spermatids [7]
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