Dynamic actin remodelling processes at the leading edge of migrating tumour cells are concerted events controlled by a fine-tuned temporal and spatial interplay of kinases and phosphatases. Actin severing is regulated by ADF/Cofilin which regulates stimulus-induced lamellipodia protrusion and directed cell motility. Cofilin is activated by dephosphorylation via phosphatases of the slingshot (SSH) family. SSH activity is strongly increased by its binding to filamentous actin (F-actin), however, other upstream regulators remain unknown. We show that in response to RhoA activation, Protein Kinase D1 (PKD1) phosphorylates the SSH enzyme SSH1L at a serine residue located in its actin binding motif. This generates a 14-3-3 binding motif, blocks the localization of SSH1L to F-actin-rich structures in the lamellipodium by sequestering it in the cytoplasm. Consequently, expression of constitutively-active PKD1 in invasive tumour cells enhanced phosphorylation of cofilin and effectively blocked the formation of free actin filament barbed ends and directed cell migration.

Macrophages infiltrating the pancreas in response to inflammation induce cellular transdifferentiation by secreting cytokines that activate NF-κB signaling and matrix metalloproteinase expression.

Protein kinase D (PKD) participates in activation of the transcription factor NF-B (nuclear factor B) in cells exposed to oxidative stress, leading to increased cellular survival. We previously demonstrated that phosphorylation of PKD at Tyr463 in the PH (pleckstrin homology) domain is mediated by the Src-Abl pathway and that it is necessary for PKD activation and subsequent NF-B induction. Here we show that activation of PKD in response to oxidative stress requires two sequential signaling events, i.e., phosphorylation of Tyr463 by Abl, which in turn promotes a second step, phosphorylation of the PKD activation loop (Ser738/Ser742). We show that this is mediated by PKC␦ (protein kinase C␦), a kinase that is activated by Src in response to oxidative stress. We also show that other PKCs, including PKC and PKC, do not participate in PKD activation or NF-B induction. We propose a model in which two coordinated signaling events are required for PKD activation. Tyrosine phosphorylation in the PH domain at Tyr463, mediated by the Src-Abl pathway, which in turn facilitates the phosphorylation of Ser738/Ser742 in the activation loop, mediated by the Src-PKC␦ pathway. Once active, the signal is relayed to the activation of NF-B in oxidative stress responses.The activation of the inducible transcription factor NF-B (nuclear factor B) is important for many cellular responses because it participates in the activation of genes such as interleukin-1 and TNF-␣ (tumor necrosis factor alpha), which contribute to efficient immune and inflammatory responses. NF-B activation has also been shown to control both pro-and antiapoptotic signaling (20,36,49). Moreover, numerous studies have shown that in a variety of cell types, NF-B acts as a sensor for oxidative stress (21,29,34). For example, cells exposed to H 2 O 2 , or induced to produce intracellular reactive oxygen species (ROS), show potent 42).Activation of NF-B is regulated by multiple distinct upstream signaling pathways, and the contribution of each pathway to NF-B induction is dependent on the nature of the cellular stimulus (20). However, one feature common to many NF-B-activating pathways is that they converge at the level of the IB kinase (IKK) signalosome, a multiprotein complex necessary for phosphorylation and down-regulation of the NF-B inhibitory protein IB. Although the signaling pathways acting upstream of the IKK complex used by proinflammatory cytokines such as TNF are well characterized, the signaling cascades that mediate oxidative stress-induced NF-B activation have remained elusive (20,29,41). Recent studies have shown that activation of NF-B in response to oxidative stress is concomitant with tyrosine phosphorylation of a number of signaling intermediates in the canonical IKK/NF-B pathway (12, 42). As an example, we recently showed that in response to oxidative stress, activation of the Src-Abl signaling module converges on the serine/threonine kinase PKD (protein kinase D), which in turn stimulates activation of NF-B (42). Moreover, tyrosine phosphorylatio...

Introduction The biological and molecular events that regulate the invasiveness of breast tumour cells need to be further revealed to develop effective therapies that stop breast cancer from expanding and metastasising.