Abstract
We have recently found that β-actin-like protein 2 (actbl2) forms complexes with gelsolin in human melanoma cells and can polymerize. Phylogenetic and bioinformatic analyses showed that actbl2 has a common origin with two non-muscle actins, which share a separate history from the muscle actins. The actin groups’ divergence started at the beginning of vertebrate evolution, and actbl2 actins are characterized by the largest number of non-conserved amino acid substitutions of all actins. We also discovered that ACTBL2 is expressed at a very low level in several melanoma cell lines, but a small subset of cells exhibited a high ACTBL2 expression. We found that clones with knocked-out ACTBL2 (CR-ACTBL2) or overexpressing actbl2 (OE-ACTBL2) differ from control cells in the invasion, focal adhesion formation, and actin polymerization ratio, as well as in the formation of lamellipodia and stress fibers. Thus, we postulate that actbl2 is the seventh actin isoform and is essential for cell motility.
Highlights
We have recently found that β-actin-like protein 2 forms complexes with gelsolin in human melanoma cells and can polymerize
Abbreviations actin-binding proteins (ABPs) Actin binding proteins ACTA1 Gene coding for α skeletal actin ACTA2 Gene coding for α smooth actin ACTB Gene coding for β non-muscle actin ACTBL2 Gene coding for actbl[2] (β-actin-like protein 2) actbl[2] β-actin-like protein 2; the product of ACTBL2 ACTC1 Gene coding for α cardiac actin ACTG1 Gene coding for γ non-muscle actin ACTG2 Gene coding for γ smooth actin CR-ACTBL2 Cells with knocked out ACTBL2 CR-CTRL Control cells focal adhesions (FAs) Focal adhesion F-actin Fetal bovine serum FBS Filamentous actin G-actin Globular actin gDNA Genomic DNA lysophosphatidic acid (LPA) Lysophosphatidic Acid nFA Nascent focal adhesion OE-ACTBL2 Cells with actbl[2] overexpression obtained three control clones (OE-CTRL) Control cells
We found that ACTBL2 had a common ancestor with two other non-muscle actin isoforms, and sequences most similar to ACTBL2 are present in marsupials and placental mammals, but sequences showing similarity to them can be found in earlier diverged vertebrate lineages up to cartilaginous fishes
Summary
We have recently found that β-actin-like protein 2 (actbl2) forms complexes with gelsolin in human melanoma cells and can polymerize. Hoedebeck et al.[14] have shown that the silencing of ACTBL2 leads to diminished motility of human arterial smooth muscle cells These authors demonstrated that the expression of ACTBL2 in smooth muscle cells under stretch conditions depends on the nuclear factor 5 of activated T-cells (NFAT5). Because there is scant published data concerning actbl[2], we decided to investigate its role in human melanoma cells in terms of their 2D and 3D motility and ability to form focal adhesions. We obtained stable A375 clones, either devoid of actbl[2] or overexpressing actbl[2] We chose these cells as they are among the best-studied human melanoma cells
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