Role of Titin in Nonmuscle and Smooth Muscle Cells

Keller, Thomas C. S.; Eilertsen, Kenneth J.; Higginbotham, M; Kazmierski, Steven T.; Kim, K T; Velichkova, Michaella

doi:10.1007/978-1-4615-4267-4_16

Cited by 22 publications

(14 citation statements)

References 18 publications

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“…Whether Z-repeat and Zq domains are present in any adult smooth muscle titin isoforms recently was brought into doubt, however, by an investigation that revealed the presence of smooth muscle transcripts containing sequence from only 80 -90 titin gene exons and excluding the Z-repeat-and Zq-encoding exons (19). We used RT-PCR analysis and antibody detection to confirm the presence of these domains in the long adult smooth muscle titin isoform that we originally characterized as smitin (18,33) and now call sm-titin. RT-PCR analysis of human carotid artery RNA yielded products encoding Z-repeats Zr1, Zr2, Zr3, and Zr7 and the Zq domain.…”

Section: Discussionmentioning

confidence: 99%

Smooth Muscle Titin Zq Domain Interaction with the Smooth Muscle α-Actinin Central Rod

Richard

Simon

Bienkiewicz

et al. 2008

Journal of Biological Chemistry

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Actin-myosin II filament-based contractile structures in striated muscle, smooth muscle, and nonmuscle cells contain the actin filament-cross-linking protein ␣-actinin. In striated muscle Z-disks, ␣-actinin interacts with N-terminal domains of titin to provide a structural linkage crucial for the integrity of the sarcomere. We previously discovered a long titin isoform, originally smitin, hereafter sm-titin, in smooth muscle and demonstrated that native sm-titin interacts with C-terminal EF hand region and central rod R2-R3 spectrin-like repeat region sites in ␣-actinin. Reverse transcription-PCR analysis of RNA from human adult smooth muscles and cultured rat smooth muscle cells and Western blot analysis with a domain-specific antibody presented here revealed that sm-titin contains the titin geneencoded Zq domain that may bind to the ␣-actinin R2-R3 central rod domain as well as Z-repeat domains that bind to the EF hand region. We investigated whether the sm-titin Zq domain binds to ␣-actinin R2 and R3 spectrin repeat-like domain loops that lie in proximity with two-fold symmetry on the surface of the central rod. Mutations in ␣-actinin R2 and R3 domain loop residues decreased interaction with expressed sm-titin Zq domain in glutathione S-transferase pull-down and solid phase binding assays. Alanine mutation of a region of the Zq domain with high propensity for ␣-helix formation decreased apparent Zq domain dimer formation and decreased Zq interaction with the ␣-actinin R2-R3 region in surface plasmon resonance assays. We present a model in which two sm-titin Zq domains interact with each other and with the two R2-R3 sites in the ␣-actinin central rod.

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Section: Discussionmentioning

confidence: 99%

Smooth Muscle Titin Zq Domain Interaction with the Smooth Muscle α-Actinin Central Rod

Richard

Simon

Bienkiewicz

et al. 2008

Journal of Biological Chemistry

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“…Unlike MHCs, tropomysin, and troponin‐T proteins, we found that the titin protein is not down‐regulated in mature electrocytes and its presence, despite the absence of sarcomeric structures, was unexpected. However, although titin plays a key role in establishing and maintaining the integrity of the contractile sarcomere unit in muscle fibers, it is also found interweaved throughout the cytoskeletal network of nonmuscle cells (45, 46). Hence, titin may be retained in electrocytes to work in concert with other cytoskeletal proteins, i.e., desmin and keratin, to help sustain their structural morphology (44).…”

Section: Discussionmentioning

confidence: 99%

Evidence of post‐transcriptional regulation in the maintenance of a partial muscle phenotype by electrogenic cells of S.macrurus

Cuellar¹,

Kim²,

Unguez³

2006

FASEB j.

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Electrocytes, the current-producing cells of electric organs (EOs) in electric fish, are unique in that they derive from striated muscle and they possess biochemical characteristics of both muscle and non-muscle cells. In the freshwater teleost Sternopygus macrurus, electrocytes are multinucleated cells that do not contract yet retain expression of some proteins common to skeletal muscle cells. Given the role that transcriptional regulation plays in the activation of the myogenic program in vertebrates, we examined the expression patterns of several genes associated with multiple functions of skeletal muscle in mature electrocytes of S. macrurus. Our expression analyses detected transcripts for alpha-actin, alpha-acetylcholine (ACh) receptor (alpha-AChR), desmin, muscle creatine kinase (MCK), myosin heavy chain (MHC) isoforms, titin, tropomyosin, and troponin-T genes in the EO. However, immunolabeling studies revealed that electrocytes do not contain MCK, MHCs, or tropomyosin or troponin-T proteins. These results underscore the contribution of gene regulatory mechanisms in the maintenance of the muscle-like phenotype of EO that may be transcriptional-independent. We also report the classification and frequency of distinct transcripts from a random selection of 420 clones from an EO cDNA library. This is the first characterization of expressed genes in an EO, and it is an important step toward identifying mechanisms that affect different muscle protein systems for the evolution of highly specialized noncontractile tissues. Evidence of post-transcriptional regulation in the maintenance of a partial muscle phenotype by electrogenic cells of S. macrurus.

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“…We previously isolated a very high molecular weight protein from extracts of intestinal epithelial cell brush borders [Eilertsen and Keller, III, 1992;Eilertsen et al, 1994] and human blood platelets [Keller, III et al, 2000]. This protein was named cellular titin (ctitin) because of its similarity in size and molecular Fig.…”

Section: Cellular Titin-a Titin Isoformmentioning

confidence: 99%

“…Previously, our lab has identified a titin-like protein (cellular titin, c-titin) in nonmuscle cells, first in the terminal web domain of the intestinal cell brush border cytoskeleton and then in human blood platelets [Eilertsen and Keller, III, 1992;Keller, III et al, 2000]. Characterization of c-titin isolated from brush borders and platelets revealed that it interacts with a-actinin and arranges nonmuscle myosin II bipolar filaments in a side-by-side and end-to-end ordered array similar to that of myosin II organization in the stress fibers of nonmuscle cells [Eilertsen and Keller, III, 1992;Eilertsen et al, 1994].…”

Section: Introductionmentioning

confidence: 99%

Molecular identification and localization of cellular titin, a novel titin isoform in the fibroblast stress fiber

Cavnar

Olenych

Keller

2007

Cell Motil. Cytoskeleton

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We previously discovered a large titin-like protein-c-titin-in chicken epithelial brush border and human blood platelet extracts that binds alpha-actinin and organizes arrays of myosin II bipolar filaments in vitro. RT-PCR analysis of total RNA from human megakaryoblastic (CHRF-288-11) and mouse fibroblast (3T3) nonmuscle cells reveal sequences identical to known titin gene exon sequences that encode parts of the Z-line, I-band, PEVK domain, A-band, and M-line regions of striated muscle titins. In the nonmuscle cells, these sequences are differentially spliced in patterns not reported for any striated muscle titin isoform. Rabbit polyclonal antibodies raised against expressed protein fragments encoded by the Z-repeat and kinase domain regions react with the c-titin band in Western blot analysis of platelet extracts and immunoprecipitate c-titin in whole platelet extracts. Immunofluorescent localization demonstrates that the majority of the c-titin colocalizes with alpha-actinin and actin in 3T3 and Indian Muntjac deer skin fibroblast stress fibers. Our results suggest that differential expression of titin gene exons in nonmuscle cells yields multiple novel isoforms of the protein c-titin that are associated with the actin stress fiber structures.

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Role of Titin in Nonmuscle and Smooth Muscle Cells

Cited by 22 publications

References 18 publications

Smooth Muscle Titin Zq Domain Interaction with the Smooth Muscle α-Actinin Central Rod

Smooth Muscle Titin Zq Domain Interaction with the Smooth Muscle α-Actinin Central Rod

Evidence of post‐transcriptional regulation in the maintenance of a partial muscle phenotype by electrogenic cells of S.macrurus

Molecular identification and localization of cellular titin, a novel titin isoform in the fibroblast stress fiber

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