Prelamin-A/C, or lamin A/C is a protein that in humans is encoded by the LMNA gene. [5] [6] [7] Lamin A/C belongs to the lamin family of proteins.
Prelamin-A/C, or lamin A/C is a protein that in humans is encoded by the LMNA gene. [5] [6] [7] Lamin A/C belongs to the lamin family of proteins.
In the setting of ZMPSTE24 deficiency, the final step of lamin processing does not occur, resulting in an accumulation of farnesyl-prelamin A. In Hutchinson–Gilford progeria syndrome, a 50-amino acid deletion in prelamin A (amino acids 607–656) removes the site for the second endoproteolytic cleavage. Consequently, no mature lamin A is formed, and a farnesylated mutant prelamin A (progerin) accumulates in cells. [9] The nuclear lamina consist of a two-dimensional matrix of proteins located next to the inner nuclear membrane. The lamin family of proteins make up the matrix and are highly conserved in evolution. During mitosis, the lamina matrix is reversibly disassembled as the lamin proteins are phosphorylated. Lamin proteins are thought to be involved in nuclear stability, chromatin structure and gene expression. Vertebrate lamins consist of two types, A and B. Through alternate splicing, this gene encodes three type A lamin isoforms. [10]
Early in mitosis, maturation promoting factor (abbreviated MPF, also called mitosis-promoting factor or M-phase-promoting factor) phosphorylates specific serine residues in all three nuclear lamins, causing depolymerization of the lamin intermediate filaments. The phosphorylated lamin B dimers remain associated with the nuclear membrane via their isoprenyl anchor. Lamin A is targeted to the nuclear membrane by an isoprenyl group but it is cleaved shortly after arriving at the membrane. It stays associated with the membrane through protein-protein interactions of itself and other membrane associated proteins, such as TOR1AIP1 (LAP1). Depolymerization of the nuclear lamins leads to disintegration of the nuclear envelope. Transfection experiments demonstrate that phosphorylation of human lamin A is required for lamin depolymerization, and thus for disassembly of the nuclear envelope, which normally occurs early in mitosis.
Mutations in the LMNA gene are associated with several diseases, including Emery–Dreifuss muscular dystrophy, familial partial lipodystrophy, limb girdle muscular dystrophy, dilated cardiomyopathy, Charcot–Marie–Tooth disease, and restrictive dermopathy. A truncated version of lamin A, commonly known as progerin, causes Hutchinson-Gilford-Progeria syndrome. [12] [13] To date over 1,400 SNPs are known . They can manifest in changes on mRNA, splicing or protein (e.g. Arg471Cys, [14] Arg482Gln, [15] Arg527Leu, [11] Arg527Cys, [16] Ala529Val [17] ) level.
DNA double-strand damages can be repaired by either homologous recombination (HR) or non-homologous end joining (NHEJ). LMNA promotes genetic stability by maintaining the levels of proteins that have key roles in HR and NHEJ. [18] [19] Mouse cells that are deficient for maturation of prelamin A have increased DNA damage and chromosome aberrations, and show increased sensitivity to DNA damaging agents. [20] In progeria, the inadequacy of DNA repair, due to defective LMNA, may cause features of premature aging (see DNA damage theory of aging).
LMNA has been shown to interact with:
Progeria is a specific type of progeroid syndrome, also known as Hutchinson–Gilford syndrome or Hutchinson–Gilford progeroid syndrome (HGPS). A single gene mutation is responsible for causing progeria. The affected gene, known as lamin A (LMNA), makes a protein necessary for holding the cell nucleus together. When this gene mutates, an abnormal form of lamin A protein called progerin is produced. Progeroid syndromes are a group of diseases that cause individuals to age faster than usual, leading to them appearing older than they actually are. People born with progeria typically live until their mid- to late-teens or early twenties. Severe cardiovascular complications usually develop by puberty, later on resulting in death.
Lamins, also known as nuclear lamins are fibrous proteins in type V intermediate filaments, providing structural function and transcriptional regulation in the cell nucleus. Nuclear lamins interact with inner nuclear membrane proteins to form the nuclear lamina on the interior of the nuclear envelope. Lamins have elastic and mechanosensitive properties, and can alter gene regulation in a feedback response to mechanical cues. Lamins are present in all animals but are not found in microorganisms, plants or fungi. Lamin proteins are involved in the disassembling and reforming of the nuclear envelope during mitosis, the positioning of nuclear pores, and programmed cell death. Mutations in lamin genes can result in several genetic laminopathies, which may be life-threatening.
Intermediate filaments (IFs) are cytoskeletal structural components found in the cells of vertebrates, and many invertebrates. Homologues of the IF protein have been noted in an invertebrate, the cephalochordate Branchiostoma.
The nuclear lamina is a dense fibrillar network inside the nucleus of eukaryote cells. It is composed of intermediate filaments and membrane associated proteins. Besides providing mechanical support, the nuclear lamina regulates important cellular events such as DNA replication and cell division. Additionally, it participates in chromatin organization and it anchors the nuclear pore complexes embedded in the nuclear envelope.
In genetics, a missense mutation is a point mutation in which a single nucleotide change results in a codon that codes for a different amino acid. It is a type of nonsynonymous substitution.
Malouf syndrome is a congenital disorder that causes one or more of the following symptoms: intellectual disability, ovarian dysgenesis, congestive cardiomyopathy, broad nasal base, blepharoptosis, and bone abnormalities, and occasionally marfanoid habitus.
Emery–Dreifuss muscular dystrophy (EDMD) is a type of muscular dystrophy, a group of heritable diseases that cause progressive impairment of muscles. EDMD affects muscles used for movement, causing atrophy, weakness and contractures. It almost always affects the heart, causing abnormal rhythms, heart failure, or sudden cardiac death. It is rare, affecting 0.39 per 100,000 people. It is named after Alan Eglin H. Emery and Fritz E. Dreifuss.
Enquiry into the evolution of ageing, or aging, aims to explain why a detrimental process such as ageing would evolve, and why there is so much variability in the lifespans of organisms. The classical theories of evolution suggest that environmental factors, such as predation, accidents, disease, and/or starvation, ensure that most organisms living in natural settings will not live until old age, and so there will be very little pressure to conserve genetic changes that increase longevity. Natural selection will instead strongly favor genes which ensure early maturation and rapid reproduction, and the selection for genetic traits which promote molecular and cellular self-maintenance will decline with age for most organisms.
Emerin is a protein that in humans is encoded by the EMD gene, also known as the STA gene. Emerin, together with LEMD3, is a LEM domain-containing integral protein of the inner nuclear membrane in vertebrates. Emerin is highly expressed in cardiac and skeletal muscle. In cardiac muscle, emerin localizes to adherens junctions within intercalated discs where it appears to function in mechanotransduction of cellular strain and in beta-catenin signaling. Mutations in emerin cause X-linked recessive Emery–Dreifuss muscular dystrophy, cardiac conduction abnormalities and dilated cardiomyopathy.
Laminopathies are a group of rare genetic disorders caused by mutations in genes encoding proteins of the nuclear lamina. Since the first reports of laminopathies in the late 1990s, increased research efforts have started to uncover the vital role of nuclear envelope proteins in cell and tissue integrity in animals. Laminopathies are a group of degenerative diseases, other disorders associated with inner nuclear membrane proteins are known as nuclear envelopathies.
Restrictive dermopathy (RD) is a rare, lethal autosomal recessive skin condition characterized by syndromic facies, tight skin, sparse or absent eyelashes, and secondary joint changes.
Protein O-mannosyl-transferase 1 is an enzyme that in humans is encoded by the POMT1 gene. It is a member of the dolichyl-phosphate-mannose-protein mannosyltransferases.
Transmembrane protein 43 is a protein that in humans is encoded by the TMEM43 gene. TMEM43 may have an important role in maintaining nuclear envelope structure by organizing protein complexes at the inner nuclear membrane. Required for retaining emerin at the inner nuclear membrane. However, the localization of TMEM43 in myocardial tissue is controversial discussed. Franke et al. demonstrated that TMEM43 is localized at the intercalated disc but not at the nuclear envelope. In contrast Christensen et al. have shown that TMEM43 is mainly localized at the sarcolemma. Mutations in TMEM43 are associated with ARVD and EDMD7.
Torsin-1A-interacting protein 1 is a protein that in humans is encoded by the TOR1AIP1 gene. More commonly known as lamina associated polypeptide 1 (LAP1), it is a type II integral membrane protein that resides in the inner nuclear membrane. The luminal domain of LAP1 interacts with Torsin A and is necessary for the ATPase activity of Torsin A. LAP1 plays a critical role in skeletal and heart muscle. Mutations in TOR1AIP1 have been linked to muscular dystrophy and cardiomyopathy. It's deletion from mouse hepatocytes leads to defected very-low density lipoprotein secretion and causes non-alcoholic fatty liver disease and non-alcoholic steatohepatitis
ZMPSTE24 is a human gene. The protein encoded by this gene is a metallopeptidase. It is involved in the processing of lamin A. Defects in the ZMPSTE24 gene lead to similar laminopathies as defects in lamin A, because the latter is a substrate for the former. In humans, a mutation abolishing the ZMPSTE24 cleavage site in prelamin A causes a progeroid disorder. Failure to correctly process prelamin A leads to deficient ability to repair DNA double-strand breaks.
Progerin is a truncated version of the lamin A protein involved in the pathology of Hutchinson–Gilford progeria syndrome. Progerin is most often generated by a sporadic single point nucleotide polymorphism c.1824 C>T in the gene that codes for matured Lamin A. This mutation activates a cryptic splice site that induces a larger mutation in the processed prelamin A messenger RNA, causing the deletion of a 50 amino-acid group near the C-terminus of the prelamin A protein. The endopeptidase ZMPSTE24 cannot cleave between the missing RSY - LLG amino acid sequence during the maturation of Lamin A, due to the deletion of the 50 amino acids which included that sequence. This leaves the intact premature Lamin A bonded to the methylated carboxyl farnesyl group creating the defective protein Progerin, rather than the desired protein matured Lamin A. Approximately 90% of all Hutchinson–Gilford progeria syndrome cases are heterozygous for this deleterious single nucleotide polymorphism within exon 11 of the LMNA gene causing the post-translational modifications to produce progerin.
Inner nuclear membrane proteins are membrane proteins that are embedded in or associated with the inner membrane of the nuclear envelope. There are about 60 INM proteins, most of which are poorly characterized with respect to structure and function. Among the few well-characterized INM proteins are lamin B receptor (LBR), lamina-associated polypeptide 1 (LAP1), lamina-associated polypeptide-2 (LAP2), emerin and MAN1.
Progeroid syndromes (PS) are a group of rare genetic disorders that mimic physiological aging, making affected individuals appear to be older than they are. The term progeroid syndrome does not necessarily imply progeria, which is a specific type of progeroid syndrome.
Veena Krishnaji Parnaik is an Indian cell biologist and the current Chief Scientist at the Centre for Cellular and Molecular Biology. She obtained her Masters in Science in medicinal biochemistry from the University of Mumbai and received her PhD from Ohio State University before moving back to India to work at the CCMB. Her research is focused on understanding the functional role of the nuclear lamina and how defects in it may lead to disorders such as progeria and muscular dystrophy.
Lamin A/C congenital muscular dystrophy (CMD) is a disease that it is included in laminopathies. Laminopathies are caused, among other mutations, to mutations in LMNA, a gene that synthesizes lamins A and C.
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