RNA sequencing of sorted cells from mouse PDAC

Pancreatic ductal adenocarcinoma (PDAC) is characterized by the presence of abundant desmoplatic stroma primarily composed of cancer-associated fibroblasts (CAFs). It is generally accepted that CAFs stimulate tumor progression and might be implicated in drug resistance and immunosuppression. Here, we have compared the transcriptional profile of PDGFRa+ CAFs isolated from genetically engineered mouse PDAC tumors with that of normal pancreatic fibroblasts (NPFs) to identify genes potentially implicated in their pro-tumorigenic properties. We report that the most differentially expressed gene, Saa3, a member of the acute-phase Serum Amyloid A (SAA) apolipoprotein family, is a key mediator of the pro-tumorigenic activity of PDGFRa+ CAFs. Whereas Saa3 competent CAFs stimulate the growth of PDAC tumor cells in an orthotopic model, Saa3 null CAFs inhibit tumor growth. Saa3 also plays a role in the cross-talk between CAFs and tumor cells. Ablation of Saa3 in pancreatic tumor cells makes them insensitive to the inhibitory effect of Saa3 null CAFs. As a consequence, germline ablation of Saa3 does not prevent PDAC tumor development in mice. The pro-tumorigenic activity of Saa3 in CAFs is mediated by Mpp6, a member of the palmitoylated membrane protein subfamily of the peripheral membrane-associated guanylate kinases. Finally, we interrogated whether these observations could be translated to a human scenario. Indeed, SAA1, the orthologue of murine Saa3, is overexpressed in human CAFs. Moreover, high levels of SAA1 in the stromal component correlate with worse survival. These findings support the concept that selective inhibition of SAA1 in CAFs may provide potential therapeutic benefit to PDAC patients. Overall design: The following groups were used: Normal Pancreatic Fibroblasts (NPFs), Cancer Associated Fibroblasts (CAFs), Saa3 KO CAFs, Saa3 WT tumor cells, Saa3 KO tumor cells. For each group at least 3 biological replicate was included in the analysis.