Deletion mutant of FGFR4 induces onion-like membrane structures in the nucleus

Abstract

The expression of several deletion mutants of fibroblast growth factor receptor 4 (FGFR4) was studied in COS-1 cells. FGFR4-mutants lacking most of the extracellular region did not efficiently reach the plasma membrane but accumulated in the endoplasmic reticulum (ER) and Golgi body. A mutant FGFR4 lacking the kinase domain as well as most of the extracellular region (ΔExt/R4Tth) had a distinct intracellular distribution. It localized in part to the nucleus, where it exhibited a striking spotted pattern. Ultrastructural studies showed that the nuclear spots consisted of several layers of membrane that were folded into onion-like structures at the nucleoplasmic side of the nuclear envelope. These intranuclear structures did not contain nuclear pores but were positive for the ER proteins calreticulin and protein disulfide isomerase, in addition to abundant ΔExt/R4Tth. Formation of the intranuclear structures was sensitive to inhibition of protein kinase C. Live microscopy of a green-fluorescent-protein/ΔExt/R4Tth fusion protein showed that the intranuclear structures were stable and immobile, suggesting that they function as deposits of the overexpressed mutant and associated membrane. The ΔExt/R4Tth protein also induced formation of densely packed membrane stacks in the cytosol and we suggest a model were the intranuclear structures are formed by invagination of ER-derived membrane stacks into the nucleus.

Intranuclear membrane structure formations by CaaX-containing nuclear proteins

“…In contrast, in the case of Nup53p a potential amphipathic α-helix at its C-terminus seems to be responsible for the induction of intranuclear membrane formation (Marelli et al, 2001). Recently a deletion mutant of fibroblast growth factor receptor was described that lacks most of its extracellular region and its kinase domain but retains its transmembrane region (Sørensen et al, 2004). This protein localized to the nucleus and induced intranuclear membranes similar to those described here.…”

Sorting Motifs Involved in the Trafficking and Localization of the PIN1 Auxin Efflux Carrier

“…The proliferation of ER-derived membrane structures, either in the cytosol or in the nucleus, has been observed previously upon the overexpression of integral ER membrane proteins, such as 3-hydroxy-3-methyl glutarylCoA reductase, cytochrome P450, and IP3 receptor, and different models have been proposed to explain their formation (Chin et al, 1982;Schunck et al, 1991;Takei et al, 1994;Koning et al, 1996). These membranous structures also were found to contain integral membrane proteins, like calnexin, an ER chaperone, but also luminal ER proteins, like BiP or PDI (Isaac et al, 2001;Sørensen et al, 2004). Since the levels of PIN1:GFP-F165A in the mutant lines were not significantly different from those of PIN1:GFP in the control plants ( Fig.…”

Intranuclear membranes induced by lipidated proteins are derived from the nuclear envelope

“…5B and D with the non-injected control E, GFP). ER marker proteins did not induce intranuclear membranes on their own when expressed NCS-related structures, the R-rings, induced by overexpression of the nucleolar chaperon Nopp140, 6 for ODVs produced in insect cells during baculovirus infection, 17 for membranes formed after overexpression of particular nuclear proteins [22][23][24][25] as well as for those membranes formed in nuclei of several pathological cells. 13 In the above-mentioned cases the membrane budding from the INM has been either followed directly by live cell imaging 6,15,22 or membrane continuity between the intranuclear membranes and the INM has been demonstrated by TEM analysis.…”

“…17 Intranuclear membranes have also been induced experimentally by overexpression of integral membrane proteins like the lamin B receptor (LBR), an INM protein, 22 or a mutant fibroblast growth factor receptor 4 that is targeted to the INM. 23 Moreover, formation of intranuclear membrane cisternae after overexpression of particular NPC proteins has been described for nucleoporin Nup153 in mammalian cells 24 and for Nup53p in yeast. 25 In all the cases either a direct continuity between INM and the intranuclear membranes has been observed or their origin from the NE/ER has been demonstrated by the presence of bona fide ER proteins in these membranes.…”

“…6,10,13 In addition, the presence of ER marker proteins within the intranuclear membrane structures has been taken as conclusive evidence for their NE/ER origin. 23,24 Overexpression of lamins leads to formation of multilayered stacked membrane cisternae. The surface of these membranes is covered by the overexpressed proteins, which in case Cos-7 cells (results not shown).…”