Signal transduction processes in T-cells and other cell types alter the phosphorylation state of cofilin, an actin-binding phosphoprotein. Whether reversible phosphorylation is responsible for the regulation of the functional activities of cofilin is not clear at present. Here we have identified the phosphoacceptor site of cofilin and analyzed the role of cofilin phosphorylation with respect to its subcellular localization. Site-directed mutagenesis studies show that phosphorylation occurs exclusively on Ser-3. Expression of non-phosphorylatable mutant cofilin proteins in NIH3T3 cells and determination of their subcellular localization by confocal laser scanning microscopy reveal that non-phosphorylated cofilin accumulates within nuclei. This analysis shows that the subcellular localization of cofilin depends on the phosphorylation state of Ser-3.
"rylation sug - gests that cofilin is phosphorylated in the tail . The phosphor - ylation dependency of cofilin translocation is supported by other studies . It was shown in NIH3T3 cells that subcellular localization of cofilin depends on the phosphorylation state of Ser - 3 , in which non - phosphorylated cofilin accumulates with - in the nuclei ( Nebl et al . 1996 ) . However , in HL - 60 cells , cofilin translocates to the plasma membrane concomitantly to activation - induced cofilin dephosphorylation ( Suzuki et al . 1995 ) . Tyrosine phosphorylation of gelsolin is mediated by PKA / Src activities and serine - phosphorylation of cofilin is mediated by PKA as we showed here , which probably phos"
[Show abstract][Hide abstract] ABSTRACT: The spermatozoon is capable of fertilizing an oocyte only after undergoing several biochemical changes in the female reproductive tract, referred to as capacitation. The capacitated spermatozoon interacts with the egg zona pellucida and undergoes the acrosome reaction, which enables its penetration into the egg and fertilization. Actin dynamics play a major role throughout all these processes. Actin polymerization occurs during capacitation, whereas prior to the acrosome reaction, F-actin must undergo depolymerization. In the present study, we describe the presence of the actin-severing protein, cofilin, in human sperm. We examined the function and regulation of cofilin during human sperm capacitation and compared it to gelsolin, an actin-severing protein that was previously investigated by our group. In contrast to gelsolin, we found that cofilin is mainly phosphorylated/inhibited at the beginning of capacitation, and dephosphorylation occurs towards the end of the process. In addition, unlike gelsolin, cofilin phosphorylation is not affected by changing the cellular levels of PIP2. Despite the different regulation of the two proteins, the role of cofilin appears similar to that of gelsolin, and its activation leads to actin depolymerization, inhibition of sperm motility and induction of the acrosome reaction. Moreover, like gelsolin, cofilin translocates from the tail to the head during capacitation. In summary, gelsolin and cofilin play a similar role in F-actin depolymerization prior to the acrosome reaction but their pattern of phosphorylation/inactivation during the capacitation process is different. Thus, for the sperm to achieve high levels of F-actin along the capacitation process, both proteins must be inactivated at different times and, in order to depolymerize F-actin, both must be activated prior to the acrosome reaction.
Cell and Tissue Research 06/2015; DOI:10.1007/s00441-015-2229-1 · 3.57 Impact Factor
"This is a tumor-promoting mechanism, since a cofilin knockdown diminishes the cloning efficiency of these cells and interference with the respective cofilin phosphatases induces apoptosis of T-lymphoma cells 71. Cofilin is also constitutively dephosphorylated in non-hematopoietic tumor cells, such as the cervix carcinoma cell line HeLa or the colon carcinoma cell line KM12 35. Within the last decade, cofilin expression and its activation state were described as determining the metastatic potential of tumor cells. "
[Show abstract][Hide abstract] ABSTRACT: Cofilin is an actin-binding protein that depolymerizes and/or severs actin filaments. This dual function of cofilin makes it one of the major regulators of actin dynamics important for T-cell activation and migration. The activity of cofilin is spatio-temporally regulated. Its main control mechanisms comprise a molecular toolbox of phospho-, phospholipid, and redox regulation. Phosphorylated cofilin is inactive and represents the dominant cofilin fraction in the cytoplasm of resting human T cells. A fraction of dephosphorylated cofilin is kept inactive at the plasma membrane by binding to phosphatidylinositol 4,5-bisphosphate. Costimulation via the T-cell receptor/CD3 complex (signal 1) together with accessory receptors (signal 2) or triggering through the chemokine SDF1α (stromal cell-derived factor 1α) induce Ras-dependent dephosphorylation of cofilin, which is important for immune synapse formation, T-cell activation, and T-cell migration. Recently, it became evident that cofilin is also highly sensitive for microenvironmental changes, particularly for alterations in the redox milieu. Cofilin is inactivated by oxidation, provoking T-cell hyporesponsiveness or necrotic-like programmed cell death. In contrast, in a reducing environment, even phosphatidylinositol 4,5-bisphosphate -bound cofilin becomes active, leading to actin dynamics in the vicinity of the plasma membrane. In addition to the well-established three signals for T-cell activation, this microenvironmental control of cofilin delivers a modulating signal for T-cell-dependent immune reactions. This fourth modulating signal highly impacts both initial T-cell activation and the effector phase of T-cell-mediated immune responses.
"Several studies have demonstrated an increase in cofilin amounts or in activity (dephosphorylated form) in cancer cells including cell lines derived from T-cell lymphoma (Jurkat) and carcinomas from the cervix (HeLa), colon (KM12), liver (HepG2) and kidney (COS1) , and in clinical tumor samples of oral squamous-cell carcinoma , renal cell carcinoma  and ovarian cancer . In addition, overexpression of cofilin increases velocity of cell migration in Dictyostelium and human glioblastoma cells . "
[Show abstract][Hide abstract] ABSTRACT: ADF/cofilin proteins are key modulators of actin dynamics in metastasis and invasion of cancer cells. Here we focused on the roles of ADF and cofilin-1 individually in the development of polarized migration of rat mammary adenocarcinoma (MTLn3) cells, which express nearly equal amounts of each protein. Small interference RNA (siRNA) technology was used to knockdown (KD) the expression of ADF and cofilin-1 independently.
Either ADF KD or cofilin KD caused cell elongation, a reduction in cell area, a decreased ability to form invadopodia, and a decreased percentage of polarized cells after 180 s of epidermal growth factor stimulation. Moreover, ADF KD or cofilin KD increased the rate of cell migration and the time of lamellipodia protrusion but through different mechanisms: lamellipodia protrude more frequently in ADF KD cells and are more persistent in cofilin KD cells. ADF KD cells showed a significant increase in F-actin aggregates, whereas cofilin KD cells showed a significant increase in prominent F-actin bundles and increased cell adhesion. Focal adhesion area and cell adhesion in cofilin KD cells were returned to control levels by expressing exogenous cofilin but not ADF. Return to control rates of cell migration in ADF KD cells was achieved by expression of exogenous ADF but not cofilin, whereas in cofilin KD cells, expression of cofilin efficiently rescued control migration rates.
Although ADF and cofilin have many redundant functions, each of these isoforms has functional differences that affect F-actin structures, cell adhesion and lamellipodial dynamics, all of which are important determinants of cell migration.
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