Pancreatic ductal adenocarcinoma is a genetically complex disease characterized by the accumulation of genetic alterations and by extensive genomic and transcriptomic alterations leading to cell cycle deregulation, cell survival, invasion and metastasis 
. We now provide compelling evidence that GATA6
copy number gain is an additional and recurrent genetic alteration to be considered for this tumor type, and contributes oncogenic signals by virtue of its enhancement of Wnt signaling.
Although Wnt signaling is aberrantly activated in PDAC 
, mutations of CTNNB1
or other pathway components are rare in this tumor type suggesting alternative mechanisms for Wnt activation. At least two additional pathways known to be active in PDAC have also been reported as converging on the Wnt pathway 
. For example, a recent study has reported that ataxia-telangiectasia group D complementing gene (ATDC) has oncogenic potential through stabilizing ß-catenin and activating the Wnt pathway in PDAC 
whereas in a mouse model of pancreatic carcinoma activation of Hedgehog signaling led to a corresponding activation of Wnt signaling in part due to upregulation of TCF4 expression 
. This is consistent with our data as well as we demonstrate Wnt pathway activation due to transcriptional repression by GATA6 of the secreted Wnt antagonist DKK1. At the very least, the upregulation of Wnt activity mediated by GATA6 dependent repression of DKK1 further supports the view that GATA6 is an oncogene in pancreatic ductal adenocarcinoma.
amplification has been reported in pancreatic cancer cell lines and xenografts 
, when GATA6
amplification occurs during the step-wise progression of pancreatic intraepithelial neoplasia has not. We now show that GATA6 amplification occurs during the late stages of pancreatic intraepithelial neoplasia, specifically PanIN-3. Amplification lead to increased expression in these same lesions, and parallels prior observations GATA6 protein overexpression in pancreatic intraepithelial neoplasia and cancer 
. Perhaps the most important implication of this finding is that detectable GATA6
copy number gain may have value as a diagnostic marker of PDAC while still in the curative stage, as this remains a critical hurdle to improving survival of this disease 
. However, as genetic gain of GATA6
was only identified in a third of samples, a more universal and sensitive marker of canonical Wnt signaling dysregulation may be of value for this purpose.
We also noted a significant relationship among GATA6
copy number and overall survival, in that patients whose resected cancers had a copy number ≥2.3, or nuclear overexpression, had a longer overall survival than those patients without copy number gain. Although the biologic significance of this finding remains to be discerned, it is conceivable that PDACs with high GATA6
copy number, and/or simply with active canonical Wnt signaling for which GATA6
copy number is a marker, cosegregate with those PDACs with less aggressive features as we have recently shown for E-cadherin 
. It is also important to note that proliferative rates alone do not fully represent aggressive biology (metastasis), an interpretation that is in keeping with our published data that pancreatic cancers with low metastatic ability (<10 metastases at autopsy) are actually larger at diagnosis, are more invasive into surrounding tissues than those with highly metastatic ability, yet are often associated with a longer overall survival 
. In addition to its role in Wnt signaling, ß-catenin is also a critical component of the adherens junction complex that includes E-cadherin, p120, plakoglobin and γ-catenin. Binding of ß-catenin to γ-catenin links the adherens junction complex to the actin cytoskeleton, thereby providing mechanical stability 
, whereas disruption of this complex is associated with epithelial-mesenchymal transition and aggressive features in a variety of tumor types, including PDAC 
. One interpretation is that the presence of canonical Wnt pathway activity together with an intact zona-adherens in PDAC, both that are dependent on ß-catenin expression, may be linked to less aggressive features than when ß-catenin expression is lost 
DKK1 belongs to the Dickkopf family comprised of four members that include DKK2, DKK3 and DKK4. With exception of DKK3, all members have the ability to modulate Wnt signaling through inhibiting the Wnt co-receptor LRP5/6 at the cell surface leading to destabilization of ß-catenin and its subsequent degradation 
. Quantitative analysis indicated that DKK1 was the predominant member of this gene family expressed in PDAC cell lines, consistent with Takahashi et al 
. Although that study did suggest DKK1 upregulation functions as an oncogene in PDAC cells, it is important to note that only Suit-2 and a related cell line were used in that study that was not used in the current work, and the levels of GATA6 in Suit-2 are unknown. By contrast, our data has relied on multiple cell lines selected based on GATA6 and DKK1 expression levels and Wnt signaling levels. Therefore it is conceivable that the conclusions drawn based use of the Suit-2 cell line, while valid, are not fully representative of DKK1 regulation in PDAC.
In summary, GATA6 contributes to PDAC through activation of the canonical Wnt signaling pathway. This finding expands upon recent observations of GATA6 amplification, and provides fertile ground for additional studies of the role of GATA transcription factors and Wnt signaling in this pathogenesis and aggressiveness of this tumor type.