Phospholipase D1 Drives a Positive Feedback Loop to Reinforce the Wnt/β-Catenin/TCF Signaling Axis

Abstract

Activation of the Wnt signaling pathway occurs frequently in human cancers, but an understanding of the targets and regulation of this important pathway remains incomplete. In this study, we report that phospholipase D (PLD), a cell survival mediator that is upregulated in cancer, is an important target of the Wnt signaling pathway that functions in a positive feedback loop to reinforce pathway output. PLD1 expression and activity was enhanced by treatment with Wnt3a and glycogen synthase kinase-3 inhibitors, and the Wnt pathway-regulated transcription factors β-catenin and TCF-4 were required for this effect. Three functional TCF-4-binding sites were identified within the PLD1 promoter. Interestingly, suppressing PLD1 blocked the ability of β-catenin to transcriptionally activate PLD1 and other Wnt target genes by preventing β-catenin/ TCF-4 complex formation. Conversely, tactics to elevate intracellular levels of phosphatidic acid, the product of PLD1 enzyme activity, enhanced β-catenin/TCF-4 complex formation as well as β-catenin-dependent TCF transcriptional activity. In cell-based assays, PLD1 was necessary for the anchorage-independent growth driven by Wnt/β-catenin signaling, whereas β-catenin/TCF-4 was necessary for the anchorage-independent growth driven by PLD1 activation. Taken together, our findings define a function for PLD1 in a positive feedback loop of Wnt/β-catenin/TCF-4 signaling that provides new mechanistic insights into cancer, with implications of novel strategies to disrupt Wnt signaling in cancer. Cancer Res; 70(10); 4233-42. ©2010 AACR.

Phospholipase D Meets Wnt Signaling: A New Target for Cancer Therapy

“…We recently identified transcriptional activation of PLD by Wnt3a, and the second messenger PA produced by PLD further induced activation of the Wnt/b-catenin-signaling target genes via promotion of the b-catenin/TCF-4 transcription complex (4,5). We found that the expression levels of PLD and b-catenin are significantly correlated in colorectal cancer tissues, which supports the presence of a strong link between the Wnt/b-catenin pathway and PLD in vivo.…”

“…4,[13][14][15][16][17][18]. Considering the role for PLD in tumor progression, PLD inhibitors have emerged as potential anticancer drugs.…”

“…Isoform-selective or dual-specific small molecular PLD inhibitors have recently been developed and characterized (19,20). PLD inhibitors reduced invasiveness and anchorage-independent growth in metastatic breast and colorectal cancer models (4,19). Therefore, PLD inhibitors have potential for use in the treatment of cancers directly or indirectly associated with PLD.…”

“…Although PLD1 and PLD2 show structural similarities, modes of activation and functional roles of these proteins are distinct. Our recent studies show that both PLD1 and PLD2 are novel target genes of b-catenin/TCF (4,5). PLD and PA have been implicated in a diverse range of pathophysiologic processes, such as inflammation and phagocytosis, diabetes, oncogenesis, and metastasis (3).…”

Phospholipase D Signaling Pathways and Phosphatidic Acid as Therapeutic Targets in Cancer

“…The Wnt pathway is critical in tissue development and is frequently mutated in many cancers (Kikuchi, 2003). Recent studies have shown that PLD1 is a transcriptional product of Wnt activation and participates in a feed-forward mechanism in which PLD activity is required for transcription of a number of Wnt-responsive genes (Kang et al, 2010). Although EMT gene expression was not measured in the study, PLD may potentially regulate EMT and loss of adhesion through Wnt.…”