Loss of cell–cell contacts induces NF‐κB via RhoA‐mediated activation of protein kinase D1

Abstract Cell–cell contacts mediated by cadherins are known to inhibit the small Rho‐GTPase RhoA. We here show that in epithelial cells the disruption of these cell–cell contacts as mediated by a calcium switch leads to actin re‐organization and the activation of RhoA. We identified the serine/threonine kinase protein kinase D1 (PKD1) as a downstream target for RhoA in this pathway. After disruption of cell–cell contacts, PKD1 relayed RhoA activation to the induction of the transcription factor NF‐κB. We found that a signaling complex composed of the kinases ROCK, novel protein kinase C (nPKC), and Src family kinases (SFKs) is upstream of PKD1 and crucial for RhoA‐mediated NF‐κB activation. In conclusion, our data suggest a previously undescribed signaling pathway of how RhoA is activated by loss of cell–cell adhesions and by which it mediates the activation of NF‐κB. We propose that this pathway is of relevance for epithelial tumor cell biology, where loss of cell–cell contacts has been implicated in regulating cell survival and motility. J. Cell. Biochem. 106: 714–728, 2009. © 2009 Wiley‐Liss, Inc.