Research article

Dynacortin facilitates polarization of chemotaxing cells

Cathryn Kabacoff¹ , Yuan Xiong² , Runa Musib^1,3 , Elizabeth M Reichl^1,4 , John Kim¹ , Pablo A Iglesias² and Douglas N Robinson¹

¹Department of Cell Biology, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA

²Department of Electrical and Computer Engineering, Johns Hopkins University, Baltimore, MD, USA

³Current address: The Henry M. Jackson Foundation for the Advancement of Military Medicine, VPRP/DAIDS/NIAD, 6700-A Rockledge Drive, Room 42A165, Bethesda, MD, USA

⁴Current address: Human Genome Sciences, Inc. 14200 Shady Grove Road, Rockville, MD, USA

author email corresponding author email

BMC Biology 2007, 5:53doi:10.1186/1741-7007-5-53

Published:	26 November 2007

Abstract

Background

Cell shape changes during cytokinesis and chemotaxis require regulation of the actin cytoskeletal network. Dynacortin, an actin cross-linking protein, localizes to the cell cortex and contributes to cortical resistance, thereby helping to define the cell shape changes of cytokinesis. Dynacortin also becomes highly enriched in cortical protrusions, which are sites of new actin assembly.

Results

We studied the effect of dynacortin on cell motility during chemotaxis and on actin dynamics in vivo and in vitro. Dynacortin enriches with the actin, particularly at the leading edge of chemotaxing cells. Cells devoid of dynacortin do not become as polarized as wild-type control cells but move with similar velocities as wild-type cells. In particular, they send out multiple pseudopods that radiate at a broader distribution of angles relative to the chemoattractant gradient. Wild-type cells typically only send out one pseudopod at a time that does not diverge much from 0° on average relative to the gradient. Though dynacortin-deficient cells show normal bulk (whole-cell) actin assembly upon chemoattractant stimulation, dynacortin can promote actin assembly in vitro. By fluorescence spectroscopy, co-sedimentation and transmission electron microscopy, dynacortin acts as an actin scaffolder in which it assembles actin monomers into polymers with a stoichiometry of 1 Dyn₂:1 actin under salt conditions that disfavor polymer assembly.

Conclusion

Dynacortin contributes to cell polarization during chemotaxis. By cross-linking and possibly stabilizing actin polymers, dynacortin also contributes to cortical viscoelasticity, which may be critical for establishing cell polarity. Though not essential for directional sensing or motility, dynacortin is required to establish cell polarity, the third core feature of chemotaxis.