Introduction
Pancreatic ductal adenocarcinoma (PDAC) is one of the leading causes of cancer-associated mortality in developed countries with a 5-year survival rate of less than 10%. Despite extensive research, there is still a lack of reliable biomarkers for early disease detection and pathophysiology. Therefore, the minute delineation of intimate molecular mechanisms involved in the intratumoral interplay between different compartments of PDAC became of paramount importance. DKK3 (Dickkopf-3), one of the main modulators of Wnt signaling, is a rather unique protein: in PDAC, suppression of DKK3 in a Trp53-deficient context negatively impacts tumor progression and prolongs survival. We previously identified DKK3 as a novel factor for organ regeneration during pancreatitis and, through state-of-the-art investigations involving a in vivo models, delineated a direct, previously unknown link between DKK3 and the canonical-Wnt- and Hedgehog-signaling. This, and given that pancreatitis renders as a risk factor for pancreatic cancer, prompted us to investigate the potential role of DKK3 in PDAC development.
Aims & Methods
To investigate the role of DKK3 in PDAC progression, we employed cutting-edge in vivo, in vitro, and ex vivo experimental settings at different stages of KRAS-driven tumorigenesis (from early dysplasia to cancer stage). In line, a KRAS-driven PDAC mouse model (LSL-KrasG12D/+; Ptf1aCre/+) harboring wildtype Dkk3 allele (KC), heterozygous Dkk3 deletion (DKC) or homozygous Dkk3 deletion (DDKC) was involved. To specifically examine stage-specific roles of DKK3, we characterized the mice at different stages, from development of early dysplasia (10 weeks) until invasive PDAC (36 weeks). To dissect the DKK3 compartment-specific role at early and late stages within the epithelial compartment, functional assays were conducted on acinar and tumor cells respectively. Comprehensive co-culture systems employing stellate and tumor cells were utilized to characterize the intratumoral heterogeneity traits.
Results
The phenotyping of mice revealed that DKCs and DDKCs animals displayed significantly more acinar-to-ductal metaplasia (ADM) and precursor lesions from 10 weeks onward. These lesions translated in a substantial PDAC invasiveness at 36 weeks, and negatively impacted the survival and metastasis at end stage. Additionally, the loss of DKK3 positively correlated with a higher fibrotic content, a key characteristic of PDAC tumorigenesis. In line, ex vivo ADM assays demonstrated a significantly increased capacity of DKK3-null acinar cells to form ductal structures. Additionally, functional assays employing knockout tumor cells revealed higher mesenchymal marker expression such as Vimentin and N cadherin, increased invasion and migration compared to KC, in line with increased metastasis at the end stage. Furthermore, DDKC tumor cells were able to redraft the fibroblast compartment and thus, to give rise to more myofibroblasts that could likely contribute to the tumor aggressiveness at the end stages.
Conclusion
Overall, we show a multifaceted role of DKK3 in pancreatic cancer progression, and especially highlight its tumor-restraining capability within the epithelial compartment as a moderator of early tumor initiating events. This could potentially enable DKK3 to rise as a novel stage-specific biomarker for early PDAC detection.
