The nuclear membrane proteome: extending the envelope

Abstract

The marriage of proteomics with cell biology has produced extensive inventories of the proteins that inhabit several subcellular organelles. Recent proteomic analysis has identified a large number of new putative transmembrane proteins in the nuclear envelope, and transcriptome profiling suggests that the nuclear membrane proteome exhibits some significant variations among different tissues. Cell type-specific differences in the composition of protein subcomplexes of the nuclear envelope, particularly those containing the disease-associated protein lamin A, could yield distinctive functions and so explain the tissue-specificity of a diverse group of nuclear envelope-linked disorders in humans. Considered together, these recent results suggest an unexpected functional complexity at the nuclear envelope.3 An introduction to the nuclear envelopeThe past few years have seen an explosion in the number of identified nuclear envelope (NE) proteins as well as in the number of their associated diseases. The NE (Figure 1), which is continuous with the more peripheral ER, contains an outer (ONM) and inner nuclear membrane (INM) that are joined at the nuclear pore membrane, giving rise to three different subdomains within nuclear membranes. The ONM is functionally similar to the more peripheral ER, but also is thought to contain some distinct resident proteins. The INM contains a large group of distinctive transmembrane proteins and is lined by a polymer of intermediate filament proteins called lamins. As many as four major lamin subtypes (lamin A, C, B1, and B2) are expressed in mammalian cells in a developmentally-regulated manner. Most lamin subtypes can be modified with lipid moieties that facilitate their targeting to the NE, and a fraction of some lamins occurs in the nucleoplasm as well as at the INM (reviewed in [1]). The lamin polymer and interacting proteins at the INM collectively comprise the nuclear lamina. The nuclear pore membrane is closely associated with nuclear pore complexes (NPCs), the main macromolecular transport channels across the NE. The transport functions and proteome of the NPC have been extensively characterized [2,3], and will not be further considered here. It is generally agreed that the lamina has a role in nuclear morphology and stability [4][5][6], and support for a wide and ever-increasing array of additional functions has emerged from recent studies. Lamins and lamina-associated membrane proteins have been linked to activities as diverse as transcription [7][8][9][10], DNA replication [11,12], nuclear anchoring/ migration within the cell [13], and signaling cascades [14]. To what extent these are direct or indirect effects of lamina proteins remains to be elucidated. 4Consistent with the notion that the nuclear lamina is involved in a diverse range of basic cellular functions, at least fifteen inherited diseases and syndromes have been linked to lamins A/C and certain associated NE transmembrane proteins.These include muscular dystrophies, lipodystrophies, neuropathy, cardiomyo...

Analysis of Prelamin A Biogenesis Reveals the Nucleus to be a CaaX Processing Compartment

“…Interestingly, a comprehensive study by Schirmer and colleagues to identify nuclear envelope proteins did not uncover Zmpste24 and Icmt (Schirmer et al, 2003;Schirmer and Gerace, 2005). This study used a subtractive approach to identify proteins that were enriched within nuclear envelopes.…”

“…However, our analysis using FTase antibodies does not reveal an unequivocal, concentrated nuclear signal, making the previously published indirect IF data difficult to interpret (J.B. and S.M., unpublished observation). Our observation that a prelamin A mutant that cannot be prenylated (C661S) is not cleaved after nuclear accumulation ( Figure 2C) strongly argues that FTase activity is required for lamin A processing occurring within the nucleus.Interestingly, a comprehensive study by Schirmer and colleagues to identify nuclear envelope proteins did not uncover Zmpste24 and Icmt (Schirmer et al, 2003;Schirmer and Gerace, 2005). This study used a subtractive approach to identify proteins that were enriched within nuclear envelopes.…”

Proteins that associate with lamins: Many faces, many functions

“…Yet a subset of ONM proteins is unique and not shared with the ER. The INM (although joined with the ONM at NPCs) contains its own unique group of integral membrane proteins that selectively and efficiently target to the INM [3,4]. Many of these INM proteins are components of the nuclear lamina, the core of which is formed by the nuclear-specific, type V intermediate filament lamin proteins.…”

Purification of Nuclei and Preparation of Nuclear Envelopes from Skeletal Muscle

“…The nuclear envelope (NE) is a double membrane system that includes a number of integral membrane proteins, nuclear pore complexes and the intermediate filament lamin polymer (1)(2)(3). Recently several inherited diseases, especially muscular dystrophies, have been associated with mutations in NE proteins (2,4), sparking renewed interest in the muscle NE (5).…”

“…Treatment with enzymes to digest nucleic acids followed by salt washes and pelleting through sucrose cushions reduces the relative abundance of chromatin proteins (12)(13)(14). 3 We have previously elaborated procedures specific to purification of NEs from liver and from blood cells (15,16). These and other established procedures for the isolation of nuclei from soft tissues such as liver, kidney and brain cannot be successfully applied to skeletal muscle.…”