NOVEL SPLICING ISOFORM OF ACTIN-BINDING PROTEIN ALPHA-ACTININ 4
IN EPIDERMOID CARCINOMA CELLS A431
V.Yu. Aksenova,1,* M.G. Khotin,1 L.V. Turoverova,1 N.M. Yudintseva,1
K.-E. Magnusson,2 G.P. Pinaev,1 D.G. Tentler 1
1 Institute of Cytology, RAS, St. Petersburg, Russia, and
2 Linkoping University, Sweden;
* e-mail: vasilisina@gmail.com
Alpha-actinin 4 (ACTN4) belongs to actin binding proteins of the spectrin superfamily. Structural organisation
of actin fibres and focal contacts is considered to be its primary function in a cell. Besides that, nucleocytoplasmic
shuffling of ACTN4 and its involvement in nuclear processes were demonstrated. Lately, additional
isoforms of ACTN4 resulted from an alternative splicing has been described in various cel l types and malignant
tumours. In this study, we present investigation of a novel ACTN4 isoform of 80 kDa. The isoform was found in
human epidermoid carcinoma cells A431, and it was not detected in human skin fibroblasts, normal human keratinocytes
and transformed human embryonic cells HEK293T. Analysis of ACTN4 mRNA in A431 cells showed
the presence of a splice variant that lacked the exons 2—8. The deleted exons code two calponin homology
domains responsible for ACTN4 binding to F-actin. Intracellular distribution of the described ACTN4 isoform
(ACTN4ISO) overexpressed in HEK293T cells differed from that of the full size protein. In the cytoplasm,
ACTN4ISO was allocated diffusively with no colocalisation with actin cytoskeleton structures. Intranuclear distribution
of ACTN4ISO also differed from that of the full size ACTN4. Nevertheless, immunochemical analysis
demonstrated possibility of ACTN4ISO to form heterodimers with the full size protein. Additional investigations
of novel isoform interactions with ACTN4 protein partners might clarify its functional features in A431
cells.
Key words: ACTN4, alternative splicing, A431
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