Cofilin Nuclear-Cytoplasmic Shuttling Affects Cofilin-Actin Rod Formation During Stress

Abstract

SummaryCofilin protein is involved in regulating the actin cytoskeleton during typical steady state conditions, as well as during cell stress conditions where cofilin saturates F-actin, forming cofilin-actin rods. Cofilin can enter the nucleus through an active nuclear localization signal (NLS), accumulating in nuclear actin rods during stress. Here, we characterize the active nuclear export of cofilin through a leptomycin-B-sensitive, CRM1-dependent, nuclear export signal (NES). We also redefine the NLS of cofilin as a bipartite NLS, with an additional basic epitope required for nuclear localization. Using fluorescence lifetime imaging microscopy (FLIM) and Förster resonant energy transfer (FRET) between cofilin moieties and actin, as well as automated image analysis in live cells, we have defined subtle mutations in the cofilin NLS that allow cofilin to bind actin in vivo and affect cofilin dynamics during stress. We further define the requirement of cofilin-actin rod formation in a system of cell stress by temporal live-cell imaging. We propose that cofilin nuclear shuttling is critical for the cofilin-actin rod stress response with cofilin dynamically communicating between the nucleus and cytoplasm during cell stress.

Cellular functions of the ADF/cofilin family at a glance

“…One of the mechanisms that contribute to the maintenance of nuclear actin levels is mediated by an interaction between cofilin and importin-9 (Dopie et al, 2012) (see poster). Actin does not have a classic NLS, whereas cofilins have a bipartite NLS that allows for their efficient shuttling into the nucleus (Munsie et al, 2012). Importin-9 interacts with actin in a cofilin-dependent manner (likely to be mediated through the cofilin NLS), and this interaction is crucial for the nuclear transport of actin, which in turn influences the level of transcription (see also below) (Dopie et al, 2012).…”

“…As well as an NLS, cofilin also has a nuclear export signal (NES), which mediates its transport out of the nucleus (Munsie et al, 2012). Under stress conditions, such as heat shock, osmotic stress or ATP depletion, cofilin accumulates in the nucleus where it excessively binds to, and saturates, actin filaments, resulting in the formation of cofilin-actin 'rods'.…”

“…Under stress conditions, such as heat shock, osmotic stress or ATP depletion, cofilin accumulates in the nucleus where it excessively binds to, and saturates, actin filaments, resulting in the formation of cofilin-actin 'rods'. Although this has been shown to occur mainly inside the nucleus, cytoplasmic rod formation has also been observed (Bamburg, 1999;Munsie et al, 2012). Rod formation is involved in the development of neurodegenerative disorders, such as Huntington's and Alzheimer's, as the cofilin-actin rods are part of the protein inclusions that contribute to the disruption of neurite function (Bamburg and Bernstein, 2016;Minamide et al, 2010Minamide et al, , 2000.…”

Tackling proteome changes in the longissimus thoracis bovine muscle in response to pre-slaughter stress

“…538 We also found that CFL2 (cofilin, muscle isoform) was up-modulated in response to 539 PSS. Cofilin is an isoform of the actin depolymeration factor family involved in 540 regulating the actin cytoskeleton and in other multiple facets of cellular biology [59]. It 541 has the ability to bind G-and F-actin in a 1:1 ratio of cofilin to actin and is the major 542 component of intranuclear and cytoplasmic actin rods.…”

Structure/Function Analysis of the Huntingtin N-terminus Encoded by Htt Exon 1 Using Knock-In Mouse Models

“…Together, cofilin and Htt bind nuclear actin and form many small cofilin-actin rods [114,115]. This process temporarily halts nuclear actin treadmilling, resulting in decreased ATP consumption and increased availability of cellular ATP that can subsequently contribute to additional cellular stress response mechanisms to aid in recovery from acute stress events [114,115].…”