Abstract
BackgroundAberrant activation of the canonical Wnt/β-catenin pathway occurs in almost all colorectal cancers and contributes to their growth, invasion and survival. Phopholipase D (PLD) has been implicated in progression of colorectal carcinoma However, an understanding of the targets and regulation of this important pathway remains incomplete and besides, relationship between Wnt signaling and PLD is not known.Methodology/Principal FindingsHere, we demonstrate that PLD isozymes, PLD1 and PLD2 are direct targets and positive feedback regulators of the Wnt/β-catenin signaling. Wnt3a and Wnt mimetics significantly enhanced the expression of PLDs at a transcriptional level in HCT116 colorectal cancer cells, whereas silencing of β-catenin gene expression or utilization of a dominant negative form of T cell factor-4 (TCF-4) inhibited expression of PLDs. Moreover, both PLD1 and PLD2 were highly induced in colon, liver and stomach tissues of mice after injection of LiCl, a Wnt mimetic. Wnt3a stimulated formation of the β-catenin/TCF complexes to two functional TCF-4-binding elements within the PLD2 promoter as assessed by chromatin immunoprecipitation assay. Suppressing PLD using gene silencing or selective inhibitor blocked the ability of β-catenin to transcriptionally activate PLD and other Wnt target genes by preventing formation of the β-catenin/TCF-4 complex, whereas tactics to elevate intracellular levels of phosphatidic acid, the product of PLD activity, enhanced these effects. Here we show that PLD is necessary for Wnt3a-driven invasion and anchorage-independent growth of colon cancer cells.Conclusion/SignificancePLD isozyme acts as a novel transcriptional target and positive feedback regulator of Wnt signaling, and then promotes Wnt-driven anchorage-independent growth of colorectal cancer cells. We propose that therapeutic interventions targeting PLD may confer a clinical benefit in Wnt/β-catenin-driven malignancies.
Highlights
Colorectal cancer is one of the most common malignancies, occurring in a significant percentage of the population
Alterations in the Wnt/b-catenin pathway define a key event in the pathogenesis of colon cancer. b-Catenin is a transcriptional coactivator of T cell factor (TCF)/lymphoid enhancer factor (Lef) transcription factors. b-catenin stability is regulated by a multiprotein complex that includes adenomatous polyposis coli (APC), glycogen synthase kinase 3b (GSK3b), and axin
Elevated expression of PLD1 and PLD2 has been reported in colorectal cancer tissues [9]; in particular, PLD2 expression level and its association with clinicopathological features have recently been investigated in colorectal carcinoma [10]
Summary
Colorectal cancer is one of the most common malignancies, occurring in a significant percentage of the population. More than 80% of sporadic and hereditary colorectal cancers may be caused by aberrations in the Wnt/b-catenin signaling pathway [1]–[3]. Accumulation of TCF/b-catenin leads to transcriptional activation of multiple target genes, which can contribute to development of cancer [5], [6]. Identification of direct targets of the Wnt/b-catenin signaling pathway is potentially important to understanding the central role of the Wnt/b-catenin/TCF dependent canonical pathway in tumorigenesis. Aberrant activation of the canonical Wnt/b-catenin pathway occurs in almost all colorectal cancers and contributes to their growth, invasion and survival. Phopholipase D (PLD) has been implicated in progression of colorectal carcinoma an understanding of the targets and regulation of this important pathway remains incomplete and besides, relationship between Wnt signaling and PLD is not known
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