TABLE Classes of Intermediate Filaments Their Location and Associated Diseases 2.3 Molecular Weight Examples of Type of Protein (kDa) Where Found Associated Diseases Class 1 and 2: Keratins Acid cytokeratins 40–64 All epithelial cells Epidermolysis bullosa simplex Basic cytokeratins 52–68 All epithelial cells Keratoderma disorders caused by keratin mutations Meesman corneal dystrophy Class 3: Vimentin and Vimentin-like Vimentin 55 Cells of mesenchymal origin Desmin-related myopathy (including endothelial cells, (DRM) myofbroblasts, some smooth Dilated cardiomyopathy muscle cells) and some cells of Alexander disease neuroectodermal origin Amyotrophic lateral sclerosis Desmin 53 Muscle cells; co-assembles with (ALS) nestin, synemin and paranemin Glial fbrillary acidic protein 50–52 Neuroglial cells (mainly astrocytes; (GFAP) to lesser degree, ependymal cells), Schwann cells, enteric glial cells, satellite cells of sensory ganglia, and pituicytes Peripherin 54 Peripheral neurons Class 4: Neurofilaments Neuroflament L (NF-L) 68 Neurons Charcot-Marie-tooth disease Co-assembles with NF-M or NF-H Parkinson disease Neuroflament M (NF-M) 110 Neurons Co-assembles with NF-L Neuroflament H (NF-H) 130 Neurons Co-assembles with NF-L Nestin 240 Neural stem cells, some cells of neuroectodermal origin, muscle cells Co-assembles with desmin Α-Internexin 68 Neurons Synemin Α/ΒA 182 Muscle cells Co-assembles with desmin Syncoilin 64 Muscle cells Paranemin 178 Muscle cells Co-assembles with desmin Class 5: Lamins Lamin A/CB 62–72 Nucleus of all nucleated cells Emery-Dreyfuss muscular dystrophy Lamin B 65–68 Nucleus of all nucleated cells Limb girdle muscular dystrophy Class 6: Beaded Filaments Phakinin (CP49)C 49 Eye lens fber cells Juvenile-onset cataracts Co-assembles with flesin Congenital cataracts Filesin (CP115) 115 Eye lens fber cells Co-assembles with phakinin A Synemin and synemin represent two alternative transcripts of the DMN gene. BLamin C is a splice product of lamin A. C The molecular weight of filensin/phakinin heterodimer is 131 kilodaltons.
microtubules, and intermediate filaments and are thus important in the proper assembly of the cytoskeleton. Lamins, the intermediate filaments in the nucleus, are associated with numerous proteins in the inner nuclear membrane, including emerin, lamin B receptor (LBR), nurim, and several lamina-associated polypeptides. Some of these proteins have multiple binding sites to intermediate filaments, actin, chromatin, and signaling proteins; thus, they function in chromatin organization, gene expression, nuclear architecture, and cell signaling and provide an essential link between the nucleoskeleton and cytoskeleton of the cell. Another important family of intermediate filament–associated proteins consists of desmoplakins, desmoplakinlike proteins, and plakoglobins. These proteins form the attachment plaques for intermediate filaments, an essential part of desmosomes and hemidesmosomes. The interaction of intermediate filaments with cell-to-cell and cell-toextracellular matrix junctions provides mechanical stren gth and resistance to extracellular forces. Table 2.4 summarizes the characteristics of the three types of cytoskeletal filaments.