Effect of overexpression of β- and γ-actin isoforms on actin cytoskeleton organization and migration of human colon cancer cells
Histochem Cell Biol
Effect of overexpression of β‑ and γ‑actin isoforms on actin cytoskeleton organization and migration of human colon cancer cells
Aleksandra Simiczyjew 0
Antonina Joanna Mazur 0
Agnieszka Popow‑Woz´niak 0
Maria Malicka‑Błaszkiewicz 0
Dorota Nowak 0
0 a. Simiczyjew · a. J. Mazur · a. Popow-Woz ́niak · M. Malicka-Błaszkiewicz · D. nowak (
1 ) Department of Cell Pathology, Faculty of Biotechnology, University of Wrocław , Joliot-Curie 14a, 50-383 Wrocław , Poland
actins are eukaryotic proteins, which are involved in diverse cellular functions including muscle contraction, cell motility, adhesion and maintenance of cell shape. Cytoplasmic actin isoforms β and γ are ubiquitously expressed and essential for cell functioning. However, their unique contributions are not very well understood. The aim of this study was to determine the effect of β- and γ-actin overexpression on the migration capacity and actin cytoskeleton organization of human colon adenocarcinoma Be cells. In cells overexpressing β- or γ-actin, distinct cytoskeletal actin rearrangements were observed under the laser scanning confocal microscope. Overexpressed actins localized at the submembranous region of the cell body, especially near to the leading edge and on the tips of pseudopodia. The cells transfected with plasmids containing cDna for β - or γ-actin were characterized by increased migration and invasion capacities. However, the migration velocity was statistically significantly higher only in the case of γ-actin overexpressing cells. In conclusion, the increased level of β- or γ-actin leads to actin cytoskeletal remodeling followed by an increase in migration and invasion capacities of human colon Be cells. These data suggest that expression of both actin isoforms has an impact on cancer cell motility, with the subtle predominance of γ-actin, and may influence invasiveness of human colon cancer.
actin isoforms; Cancer cells invasion; Migration
Introduction
The actin family consists of highly conservative proteins,
abundant in all eukaryotic cells. actin plays different roles
in cell functioning including cell motility, contractile ring
formation during cytokinesis, maintenance of cell shape,
signal transduction, cell adhesion, transcription and
muscle contraction
(Perrin and ervasti 2010)
. In vertebrates,
six actin isoforms are expressed. They have been
classified by both isoelectric point and primary tissue or cellular
localization and comprise β- and γ-cytoplasmic, α-skeletal,
α-cardiac, and α- and γ-smooth muscle isoactins
(Vandekerckhove and Weber 1978). Muscle actins are tissue
specific, whereas β- and γ-cytoplasmic actins are ubiquitously
present in almost all cell types and are essential for cell
survival
(Harborth et al. 2001)
. actin isoforms are products of
separate genes, although there is a high homology among
their nucleotide sequences resulting in very similar protein
primary structure. actin isoforms mirror tissue but not
species specificity
(Sheterline et al. 1995; Khaitlina 2001)
. The
differences between actin isoforms occur especially in the
most variable n-terminal region of the actin molecule. The
two cytoplasmic actin isoforms—β and γ—differ only by
four amino acids located at positions 2, 3, 4 and 10. β-actin
contains asp-asp-asp at the n-terminus and Val at
position 10 of the polypeptide chain, whereas γ-actin possesses
n-terminal tripeptide glu-glu-glu and Ile at position 10
(Vandekerckhove and Weber 1978). The proportion of
cytoplasmic actins varies and depends on the cell type
(Vandekerckhove and Weber 1978; Sheterline et al. 1995; nowak
and Malicka-Błaszkiewicz 1999)
. In most cells, regardless
of their different origins, β- and γ-actin isoforms are found
in a ratio of approximately 2:1
(Khaitlina 2007; Bergeron
et al. 2010)
. However, the β/γ isoform ratio in different
rat tissues is: 1:1 in testicles, 2.5:1 in liver and 6:1 in aorta
(Vandekerckhove and Weber 1978; nowak and
MalickaBłaszkiewicz 1999)
. Mammalian erythrocytes contain
only β-actin
(Pinder and gratzer 1983)
, whereas γ-actin
predominates in chicken auditory
hair cells (Höfer et al.
1997
). The changes in actin isoform levels in cells are often
connected with pathological processes. The changed levels
of β- and γ-actins were shown to accompany many tumor
types such as chemically induced melanoma, hepatoma,
lymphoma and breast cancer
(nowak and
MalickaBłaszkiewicz 1999; Toh et al. 1977; gabbiani et al. 1984;
Brittingham et al. 1997)
. Cytoplasmic β-actin seems to be
overexpressed in many tumors, especially in actively
moving cancer cells. This isoform level was also remarkably
increased in the case of selected, highly invasive variants
of colon cancer cells
(nowak et al. 2005)
, MDCK cells
transformed by Moloney sarcoma virus (MSV)
(le et al.
1998)
or melanoma T1C1 cells
(goidin et al. 2001)
.
However, the published data are often controversial. For
example, lymphocytes synthesize β-actin in remarkabl (...truncated)