Down-Regulation of 3-Phosphoinositide–Dependent Protein Kinase-1 Levels Inhibits Migration and Experimental Metastasis of Human Breast Cancer Cells

Abstract

High expression of 3-phosphoinositide-dependent protein kinase-1 (PDK1) has been detected in various invasive cancers. In the current study, we investigated its role in cancer cell migration and experimental metastasis. Down-regulation of PDK1 expression by small interference RNA markedly inhibited spontaneous migration and epidermal growth factor (EGF)-induced chemotaxis of human breast cancer cells. The defects were rescued by expressing wild-type PDK1. PDK1-depleted cells showed impaired EGF-induced actin polymerization and adhesion, probably due to a decrease in phosphorylation of LIM kinase/cofilin and integrin β1. Confocal microscopy revealed that EGF induced cotranslocation of PDK1 with Akt and protein kinase Cζ (PKCζ), regulators of LIM kinase, and integrin β1. Furthermore, PDK1 depletion dampened EGF-induced phosphorylation and translocation of Akt and PKCζ, suggesting that Akt and PKCζ functioned downstream of PDK1 in the chemotactic signaling pathway. In severe combined immunodeficiency mice, PDK1-depleted human breast cancer cells formed more slowly growing tumors and were defective in extravasation to mouse lungs after i.v. injection. Our results indicate that PDK1 plays an important role in regulating the malignant behavior of breast cancer cells, including their motility, through activation of Akt and PKCζ. Thus, PDK1, which increases its expression in cancer cells, can be used as a target for the development of novel therapies. (Mol Cancer Res 2009;7(6):944-54)

A novel regulatory mechanism links PLCγ1 to PDK1

“…6C,D). These data demonstrate that PDK1 has a role in invasion in distinct cellular models, consistent with data in literature (Pinner and Sahai, 2008;Liu et al, 2009). Stable PDK1 knock down did not affect MDA-MB-231 cell proliferation (supplementary material Fig.…”

“…PDK1 and PLCc1 have both been reported to be involved in regulation of migration and experimental metastasis of breast cancer cells (Sala et al, 2008;Liu et al, 2009). Whether these two enzymes are involved in the same signalling cascade is not known.…”

“…Despite the general assumption that these two enzymes control parallel and distinct signalling pathways, it has been reported that downregulation of either PDK1 (Liu et al, 2009) or PLCc1 (Sala et al, 2008) inhibits migration and experimental metastasis of breast cancer cells. This observation led us to the hypothesis that the two enzymes could either co-operate or act in the same signalling cascade to control these processes.…”

Silencing of PDK1 Gene Expression by RNA Interference Suppresses Growth of Esophageal Cancer

“…PKD1 siRNA down-regulates the PDK1 expression specifically in breast cancer MDA-MB-231 cells, and inhibits the cell invasion capacity obviously (Min et al, 2009). It decreases the PDK1 mRNA and protein expression in breast cancer MCF-7, Y47D and MDA-MB-231 cells, and reduces the cell invasion capacities and tumor formation capacities in mice (Liu et al, 2009). PDK1 silencing by siRNA increases the susceptibility of MCF-7 cells to chemotherapeutics (Iorns et al, 2009;Peifer et al, 2009).…”

“…Therefore, blocking the excessively activated PI3K/Akt signal transduction pathway has become the hotspot of gene therapies for malignant tumors. Inhibition of the PDK1 expression in breast cancer MCF-7 cells (Iorns et al, 2009;Liu et al, 2009), malignant glioma U87-MG cells (Bilanges et al, 2005) and colon cancer HT-29 cells by RNA interference or micromolecular inhibitors can inhibit cell proliferation and invasion capacity, induce apoptosis, and increase the susceptibility of tumors to chemotherapeutics; and meanwhile, RNAi with PDK1 shows a better effect in increasing the susceptibility of MCF-7 cells to chemotherapeutics compared with RNAi with Akt (Liang et al, 2006). These results suggest that PDK1 might be a more effective treatment target compared with Akt.…”