Molecular Characterization and Functional Analysis of Annulate Lamellae Pore Complexes in Nuclear Transport in Mammalian Cells

Abstract

Annulate lamellae are cytoplasmic organelles containing stacked sheets of membranes embedded with pore complexes. These cytoplasmic pore complexes at annulate lamellae are morphologically similar to nuclear pore complexes at the nuclear envelope. Although annulate lamellae has been observed in nearly all types of cells, their biological functions are still largely unknown. Here we show that SUMO1-modification of the Ran GTPase-activating protein RanGAP1 not only target RanGAP1 to its known sites at nuclear pore complexes but also to annulate lamellae pore complexes through interactions with the Ran-binding protein RanBP2 and the SUMO-conjugating enzyme Ubc9 in mammalian cells. Furthermore, upregulation of annulate lamellae, which decreases the number of nuclear pore complexes and concurrently increases that of annulate lamellae pore complexes, causes a redistribution of nuclear transport receptors including importin α/β and the exportin CRM1 from nuclear pore complexes to annulate lamellae pore complexes and also reduces the rates of nuclear import and export. Moreover, our results reveal that importin α/β-mediated import complexes initially accumulate at annulate lamellae pore complexes upon the activation of nuclear import and subsequently disassociate for nuclear import through nuclear pore complexes in cells with upregulation of annulate lamellae. Lastly, CRM1-mediated export complexes are concentrated at both nuclear pore complexes and annulate lamellae pore complexes when the disassembly of these export complexes is inhibited by transient expression of a Ran GTPase mutant arrested in its GTP-bound form, suggesting that RanGAP1/RanBP2-activated RanGTP hydrolysis at these pore complexes is required for the dissociation of the export complexes. Hence, our findings provide a foundation for further investigation of how upregulation of annulate lamellae decreases the rates of nuclear transport and also for elucidation of the biological significance of the interaction between annulate lamellae pore complexes and nuclear transport complexes in mammalian cells.

Ankyrin-G induces nucleoporin Nup358 to associate with the axon initial segment of neurons

“…For instance, Nup358 interacts with the red and green opsins and modulates their subcellular localization in photoreceptors (Ferreira et al, 1996). Our finding of Nup358 at the ER, however, contradicts a previous report identifying Nup358 with other nucleoporins at the annulate lamellae (AL) of neurons (Raghunayakula et al, 2015), which are membranous organelles with characteristic features of both the endoplasmic reticulum and NPCs. Our data show that AL are scarce in neurons and nucleoporins are predominantly expressed at the nuclear rim associated with NPCs.…”

“…Nup358 expression in areas other than the nuclear envelope has previously been reported in different cell types (Cordes et al, 1996;Raghunayakula et al, 2015;Sahoo et al, 2017). However, Nup358 was almost always detected together with other nucleoporins in structures known as annulate lamellae (AL), which are cytoplasmic organelles composed of ER membranous sheets with embedded pore complexes (Kessel, 1992).…”

A variation of pigmentation in the glabrous skin of dogs

“…Annulate lamellae are found in many tissues, although most frequent in rapidly dividing oocytes and cancer cells. The function of the lamellae is not fully understood, but the close resemblance to the nuclear envelope and its pores suggests a connection with RNA production (Ghadially, 2013;Kessel, 1983Kessel, , 1992Raghunayakula, Subramonian, Dasso, Kumar, & Zhang, 2015;Reipert & Kiseleva, 2012). In any case, the presence of this organelle enhances the notion that the melanocytes are dividing frequently.…”

Postmitotic annulate lamellae assembly contributes to nuclear envelope reconstitution in daughter cells

“…They possess regularly spaced AL pore complexes (ALPCs) that are morphologically similar to NPCs (28 -30). Although the AL have an antigenically distinct molecular make-up from that of NPCs and other subcellular membranes (30, 31), many ALPC components can be recognized by antibodies against NPC components (32). Furthermore, overexpressing Nups may induce AL formation in mammalian cells (33), indicating that both NPCs and ALPCs share similar components.…”