Gene expression profiles of pancreatic tumor cells and fibroblasts in mono-cultured, transwell-cocultured, and direct-cocultured conditions

Tumor cells with diverse phenotype and biological behaviors are influenced by stromal cells through secretory factors or direct cell-cell contact. Pancreatic ductal adenocarcinoma (PDAC) is characterized by extensive desmoplasia with fibroblasts as the major cell type. Although the tumor-promoting roles of paracrine factors from fibroblasts are well-studied, direct tumor-fibroblast contact mediated tumorigenesis and metastasis is a mystery in PDAC. Here, we observed enrichment of myofibroblasts in juxta-tumoral position where tumor cells gain epithelial-mesenchymal transition for invasion, that correlated with worsened prognosis in PDAC patients. Direct cell-cell contacts as forming heterocellular aggregates between fibroblasts and tumor cells were detected in primary pancreatic tumor and circulating tumor microemboli from transgenic mice and human specimens. To explore the mechanism of direct tumor-fibroblast contact mediated tumor malignancy, RNA-seq analysis was performed to compare gene expression levels of tumor cells among mono-, transwell-, or direct co-cultured conditions. 464 common up-regulated genes in BxPC-3 and SU.86.86 cells upon direct contact with fibroblasts were identified. Using the Ingenuity Pathway Analysis system, top canonical pathways associated with these genes were related to fibroblast activation and regulation of epithelial-mesenchymal transition. On the other hand, RNA sequencing data showed that top signaling pathways activated in fibroblasts upon direct contact with BxPC-3 and SU.86.86 cells (but not MIA PaCa-2 and PANC-1 cells) were calcium-dependent axonal guidance and CREB signaling. These results elucidate the interplay between tumor cells and the closely-associated fibroblasts providing potential therapeutic strategies against tumor invasion and metastasis.