Epigenetic priming targets tumor heterogeneity to shift transcriptomic phenotype of pancreatic ductal adenocarcinoma towards a Vitamin D susceptible state
As a highly heterogeneous tumor, pancreatic ductal adenocarcinoma (PDAC) exhibits non-uniform responses to therapies across subtypes. Overcoming therapeutic resistance due to tumor heterogeneity in PDAC remains a challenge. Here, we report that Vitamin D-resistant PDAC cells hijacked Vitamin D signaling to promote tumor progression, whereas epigenetic priming with glyceryl triacetate (GTA) and 5-Aza-2'-deoxycytidine (5-Aza) overcame Vitamin D resistance and shifted the transcriptomic phenotype of PDAC toward a Vitamin D-susceptible state. Increasing overall H3K27 acetylation with GTA and reducing overall DNA methylation with 5-Aza not only elevated the Vitamin D receptor (VDR) expression but also reprogrammed the Vitamin D-responsive genes. Consequently, Vitamin D inhibited cell viability and migration in the epigenetically primed PDAC cells by activating genes involved in apoptosis as well as genes involved in negative regulation of cell proliferation and migration, while the opposite effect of Vitamin D was observed in unprimed cells. Studies in genetically engineered mouse PDAC cells further validated the effects of epigenetic priming for enhancing the anti-tumor activity of Vitamin D. Using gain- and loss-of-function experiments, we further demonstrated that VDR was necessary for augmenting original Vitamin D responses, but was insufficient for shifting transcriptomic phenotype of PDAC toward a therapeutic response to Vitamin D, highlighting that both the VDR and Vitamin D-responsive genes were prerequisites for Vitamin D response. These data reveal a previously undefined mechanism in which epigenetic state orchestrates the expression of both VDR and Vitamin D-responsive genes, and determines the response to Vitamin D in PDAC. Overall design: To understand the underlying mechanism by which the epigenetic priming with GTA and 5-Aza shift the transcriptomic phenotype of PDAC towards a Vitamin D susceptible state, we treated the MiaPaca2 cells for 24 hours with DMSO(Control),  or CPT (Vitamin D analogue),  or GTA+5-Aza, or CPT+GTA+5-Aza. Total RNA was extracted using TRIzol Reagent (Invitrogen) protocol. RNA sequencing was performed by Novogene.