Plectin isoform 1b mediates mitochondrion–intermediate filament network linkage and controls organelle shape

Plectin is a versatile intermediate filament (IF)–bound cytolinker protein with a variety of differentially spliced isoforms accounting for its multiple functions. One particular isoform, plectin 1b (P1b), remains associated with mitochondria after biochemical fractionation of fibroblasts and cells expressing exogenous P1b. Here, we determined that P1b is inserted into the outer mitochondrial membrane with the exon 1b–encoded N-terminal sequence serving as a mitochondrial targeting and anchoring signal. To study P1b-related mitochondrial functions, we generated mice that selectively lack this isoform but express all others. In primary fibroblasts and myoblasts derived from these mice, we observe a substantial elongation of mitochondrial networks, whereas other mitochondrial properties remain largely unaffected. Normal morphology of mitochondria could be restored by isoform-specific overexpression of P1b in P1b-deficient as well as plectin-null cells. We propose a model where P1b both forms a mitochondrial signaling platform and affects organelle shape and network formation by tethering mitochondria to IFs.

[1]  R Y Tsien,et al.  Understanding, improving and using green fluorescent proteins. , 1995, Trends in biochemical sciences.

[2]  G. Weigel,et al.  Plectin scaffolds recruit energy-controlling AMP-activated protein kinase (AMPK) in differentiated myofibres , 2006, Journal of Cell Science.

[3]  S. Reipert,et al.  Plectin-controlled keratin cytoarchitecture affects MAP kinases involved in cellular stress response and migration , 2006, The Journal of cell biology.

[4]  R. Hauptmann,et al.  Plectin transcript diversity: identification and tissue distribution of variants with distinct first coding exons and rodless isoforms. , 1997, Genomics.

[5]  W. Neupert,et al.  Signal-Anchor Domains of Proteins of the Outer Membrane of Mitochondria , 2003, Journal of Biological Chemistry.

[6]  G. Wiche,et al.  Plectin-isoform-specific rescue of hemidesmosomal defects in plectin (-/-) keratinocytes. , 2003, The Journal of investigative dermatology.

[7]  Doron Rapaport,et al.  Finding the right organelle , 2003, EMBO reports.

[8]  A. Elbe-Bürger,et al.  Targeted ablation of plectin isoform 1 uncovers role of cytolinker proteins in leukocyte recruitment. , 2005, Proceedings of the National Academy of Sciences of the United States of America.

[9]  M. Omary,et al.  Cellular integrity plus: organelle-related and protein-targeting functions of intermediate filaments. , 2005, Trends in cell biology.

[10]  E. Fuchs,et al.  The genetic basis of epidermolysis bullosa simplex with mottled pigmentation. , 1996, Proceedings of the National Academy of Sciences of the United States of America.

[11]  G. Wiche,et al.  Role of plectin in cytoskeleton organization and dynamics. , 1998, Journal of cell science.

[12]  R. Baum,et al.  Association of mitochondria with intermediate filaments and of polyribosomes with cytoplasmic actin , 2004, Cell and Tissue Research.

[13]  R. Youle,et al.  Quantitation of mitochondrial dynamics by photolabeling of individual organelles shows that mitochondrial fusion is blocked during the Bax activation phase of apoptosis , 2004, The Journal of cell biology.

[14]  Luca Scorrano,et al.  The relationship between mitochondrial shape and function and the cytoskeleton. , 2006, Biochimica et biophysica acta.

[15]  M. Mavroidis,et al.  Muscle intermediate filaments and their links to membranes and membranous organelles. , 2007, Experimental cell research.

[16]  G. Wiche,et al.  Plectin-RACK1 (Receptor for Activated C Kinase 1) Scaffolding , 2004, Journal of Biological Chemistry.

[17]  H. Lassmann,et al.  Targeted inactivation of plectin reveals essential function in maintaining the integrity of skin, muscle, and heart cytoarchitecture. , 1997, Genes & development.

[18]  H. McBride,et al.  Import and insertion of proteins into the mitochondrial outer membrane. , 1995, European journal of biochemistry.

[19]  G. Wiche,et al.  Not just scaffolding: plectin regulates actin dynamics in cultured cells. , 1998, Genes & development.

[20]  R. Hauptmann,et al.  Unusual 5' transcript complexity of plectin isoforms: novel tissue-specific exons modulate actin binding activity. , 1999, Human molecular genetics.

[21]  H. Blau,et al.  Primary mouse myoblast purification, characterization, and transplantation for cell-mediated gene therapy , 1994, The Journal of cell biology.

[22]  N. Pfanner,et al.  Assaying protein import into mitochondria. , 2001, Methods in cell biology.

[23]  A. Krogh,et al.  Predicting transmembrane protein topology with a hidden Markov model: application to complete genomes. , 2001, Journal of molecular biology.

[24]  G. Wiche,et al.  Plectin 5'-transcript diversity: short alternative sequences determine stability of gene products, initiation of translation and subcellular localization of isoforms. , 2003, Human molecular genetics.

[25]  R. Liem,et al.  Mutations in the neurofilament light gene linked to Charcot‐Marie‐Tooth disease cause defects in transport , 2005, Journal of neurochemistry.