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The role of amino-terminal sequences in actin isoform function

English title The role of amino-terminal sequences in actin isoform function
Applicant Chaponnier Christine
Number 109879
Funding scheme Project funding
Research institution Département de Pathologie et Immunologie Faculté de Médecine / CMU Université de Genève
Institution of higher education University of Geneva - GE
Main discipline Cellular Biology, Cytology
Start/End 01.10.2005 - 31.03.2009
Approved amount 296'000.00
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Keywords (6)

myofibroblast; Isoactin; Actin polymerization; Actin Binding Proteins; Cell migration and contraction; Fibrotic diseases

Lay Summary (English)

Lay summary
The structure, assembly and dynamics of the actin cytoskeleton are essential for cell migration and cell contraction. Mammals express six actin isoforms in a tissue specific pattern. In addition to the ubiquitous - and - cytoplasmic isoforms ( - and -CYA), non muscle cells can express another isoform, i.e. -smooth muscle actin ( -SMA). Whether isoactins play distinct roles according to cellular function is still poorly understood with the exception of -smooth muscle actin (Α-SMA) expressed in myofibroblast, the cell responsible for granulation tissue contraction during wound repair.
The major goal of our research is to elucidate the function of the actin isoforms. As the main sequence differences among actin isoforms are located at their N-terminal end, we focus our investigations towards the regulation of isoactin organization through this domain.
We previously have investigated the functional significance of the N-terminus AcEEED sequence of -SMA. Using complementary tools such as, the anti- -SMA monoclonal antibody (mAb) anti- SM-1 specific for the AcEEED sequence, the sequence AcEEED intracellularly delivered using a fusion peptide (FP) and the -SMA-GFP construct, we have provided evidence that the N-terminus AcEEED of -SMA is crucial for: 1) myofibroblast contractile activity in vitro and in vivo; 2) incorporation of -SMA into stress fibers.
Recently, using newly generated monoclonal antibodies, we have investigated the distribution of - and -CYA in fibroblastic and epithelial cells. - and -CIA differ in their complete sequence by only 4 amino acid substitutions in position 1, 2, 3 and 9. Our results indicate that - and -CYA have distinct patterns of organization: -CYA is organized in parallel filaments such as in stress fibers and circular bundles at cell-cell contacts, suggesting a role for -CYA in cell attachment and cell contraction. Conversely, -CYA is organized as a meshwork in cortical and lamellipodial structures, suggesting a role for -CYA in cell motility. Small GTPase inhibition indicates that the - and -CYA arrays are under the control of Rho and Rac respectively. When fibroblastic and epithelial cells undergo isoform specific RNAi-mediated knockdown, they display profound distinct morphological changes: -CYA siRNA treated cells are highly spread displaying broad lamellipodia and lose -CYA bundles; in contrast, -CYA siRNA treated cells acquire a contractile phenotype with thick actin bundles and devoid of lamellipodial structures. Moreover, they exhibit significant changes in motility compared to the respective controls.
Our results clearly favor the importance of the N-terminus of actin isoform for function and reveal new aspects of isoactin organization that imply their functional diversity.
Direct link to Lay Summary Last update: 21.02.2013

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Associated projects

Number Title Start Funding scheme
125320 The role of amino-terminal sequences in actin isoform function 01.04.2009 Project funding
68313 The role of amino-terminal sequences in actin isoform function. 01.10.2002 Project funding