Bcl10 is a signaling protein required for activation of the NF-kappaB transcription factor. NF-kappaB is an important mediator of genotoxic stress and regulates the expression of genes required for both cell proliferation and cell death. Bcl10 is phosphorylated in vivo, however, the protein kinase or kinases responsible are not known. Here, we show that Bcl10 is phosphorylated in response to UV irradiation. UV-induced phosphorylation of Bcl10 was inhibited by the p38 stress-activated protein kinase inhibitors SB203580 and PD169316, suggesting that p38 is required for UV-mediated phosphorylation of Bcl10. (C) 2003 Elsevier Science (USA). All rights reserved.