A classical NLS and the SUN domain contribute to the targeting of SUN2 to the inner nuclear membrane

Abstract

Integral membrane proteins of the inner nuclear membrane (INM) are inserted into the endoplasmic reticulum membrane during their biogenesis and are then targeted to their final destination. We have used human SUN2 to delineate features that are required for INM targeting and have identified multiple elements that collectively contribute to the efficient localization of SUN2 to the nuclear envelope (NE). One such targeting element is a classical nuclear localization signal (cNLS) present in the N-terminal, nucleoplasmic domain of SUN2. A second motif proximal to the cNLS is a cluster of arginines that serves coatomer-mediated retrieval of SUN2 from the Golgi. Unexpectedly, also the C-terminal, lumenal SUN domain of SUN2 supports NE localization, showing that targeting elements are not limited to cytoplasmic or transmembrane domains of INM proteins. Together, SUN2 represents the first mammalian INM protein relying on a functional cNLS, a Golgi retrieval signal and a perinuclear domain to mediate targeting to the INM.

Structure of Sad1-UNC84 Homology (SUN) Domain Defines Features of Molecular Bridge in Nuclear Envelope

“…For example, SUN1 has been implicated to play a critical role for the distribution of nuclear pore complex across the nuclear surface (55), whereas SUN2 is involved in tethering mammalian meiotic telomeres to the nuclear envelope (38). The SUN domain of SUN2 contributes to localization to the inner membrane of the nuclear envelope (56), probably through association with nesprin.…”

NuclearDrosophilaCerS Schlank regulates lipid homeostasis via the homeodomain, independent of the lag1p motif

“…Keywords: ceramide synthase; Drosophila; homeodomain; importin; lipid homeostasis; nuclear function Ceramides and sphingolipids are key intermediates in diverse cellular processes for growth, stress resistance, apoptosis, neurodegeneration, insulin function, and lipid homeostasis [1][2][3][4][5].…”

“…Expression of Schlank variants containing the homeodomain without functional lag1p motif rescued the fat metabolism phenotype of schlank mutants whereas a variant with a mutated NLS site did not rescue. Thus, the homeodomain of Schlank is involved in the regulation of lipid metabolism independent of the catalytic lag1p motif.Keywords: ceramide synthase; Drosophila; homeodomain; importin; lipid homeostasis; nuclear function Ceramides and sphingolipids are key intermediates in diverse cellular processes for growth, stress resistance, apoptosis, neurodegeneration, insulin function, and lipid homeostasis [1][2][3][4][5].In synthesis of ceramide, Ceramide Synthases (CerSs) acylate a sphingoid long-chain base (LCB) with a fatty acyl-CoA of distinct length to generate (dihydro) ceramide, the backbone of all complex sphAbbreviations aa, amino acid; ASAH1, acid ceramidase; ATF2, activating transcription factor 2; cDNA, complementary DNA; CerSs, ceramide synthases; dsRNA, double-stranded RNA; ER, endoplasmic reticulum; Gal4, galactose-responsive transcription factor; GFP, green fluorescent protein; GlcT-1, glucosylceramide synthase; H215D, change in a histidine at position 215 of schlank into glutamate; INM, inner nuclear membrane; …”

Structural insights into SUN-KASH complexes across the nuclear envelope

“…Endogenous SUN2 is localized to the NE and is partly dependent on lamin A, but not lamin C, for NE retention [13]. SUN2 is targeted to the INM through classical nuclear localization signal motifs at the N-terminus and the perinuclear SUN domain at the C-terminus [14]. SUN2 appears to associate with the centrosome in a cell cycle-dependent manner.…”