The p65/RelA Subunit of NF-κB Interacts with Actin-Containing Structures

Abstract Nuclear factor—kappa B (NF-κB) is a universal transcription factor that participates in induction of a wide variety of cellular genes. In nonstimulated cells, NF-κB is sequestered in the cytoplasm. However, little is known about where NF-κB is located. We have studied the effect of inducing a reorganization of the actin filament system on NF-κB distribution, using normal and E1A+cHa-ras -transformed rat fibroblasts. This paper demonstrates that the p65/RelA subunit of NF-κB interacts with actin-containing structures. Immunofluorescence reveals that p65 is concentrated in focal contacts and along stress fibers in normal fibroblasts. Restoration of actin stress fibers in transformants spread on fibronectin is followed by reallocation of p65 to focal contacts and stress fibers, as in normal cells. The p65 is accumulated at the edge of leading lamellae in transformants spread on laminin and is redistributed to cell-to-cell contacts after a prolonged cultivation. Treatment of cells with Cytochalasin D leads to redistribution of p65 into the actin-containing aggregates. Affinity chromatography on matrix-bound F-actin confirms that p65 can bind to filamentous actin. Taken together, these data indicate that distribution of p65 in the cytoplasm depends on the state of the actin cytoskeleton and suggest an additional, yet unknown, function of the NF-κB in the cytoplasm.

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