The TGFβ-SMAD3 pathway inhibits IL-1α induced interactions between human pancreatic stellate cells and pancreatic carcinoma cells and restricts cancer cell migration

Background: The most abundant cells in the extensive desmoplastic stroma of pancreatic adenocarcinomas are the pancreatic stellate cells, which interact with the carcinoma cells and strongly influence the progression of the cancer. Tumor stroma interactions induced by IL-1 alpha/IL-1R1 signaling have been shown to be involved in pancreatic cancer cell migration. TGF beta and its receptors are overexpressed in pancreatic adenocarcinomas. We aimed at exploring TGF beta and IL-1 alpha signaling and cross-talk in the stellate cell cancer cell interactions regulating pancreatic adenocarcinoma cell migration. Methods: Human pancreatic stellate cells were isolated from surgically resected pancreatic adenocarcinomas and cultured in the presence of TGF beta or pancreatic adenocarcinoma cell lines. The effects of TGF beta were blocked by inhibitors or amplified by silencing the endogenous inhibitor of SMAD signaling, SMAD7. Pancreatic stellate cell responses to IL-1 alpha or to IL-1 alpha-expressing pancreatic adenocarcinoma cells (BxPC-3) were characterized by their ability to stimulate migration of cancer cells in a 2D migration model. Results: In pancreatic stellate cells, IL-1R1 expression was found to be down-regulated by TGF beta and blocking of TGF beta signaling re-established the expression. Endogenous inhibition of TGF beta signaling by SMAD7 was found to correlate with the levels of IL-1R1, indicating a regulatory role of SMAD7 in IL-1R1 expression. Pancreatic stellate cells cultured in the presence of IL-1 alpha or in co-cultures with BxPC-3 cells enhanced the migration of cancer cells. This effect was blocked after treatment of the pancreatic stellate cells with TGFa. Silencing of stellate cell expression of SMAD7 was found to suppress the levels of IL-1R1 and reduce the stimulatory effects of IL-1 alpha, thus inhibiting the capacity of pancreatic stellate cells to induce cancer cell migration. Conclusions: TGF beta signaling suppressed IL-1 alpha mediated pancreatic stellate cell induced carcinoma cell migration. Depletion of SMAD7 upregulated the effects of TGF beta and reduced the expression of IL-1R1, leading to inhibition of IL-1 alpha induced stellate cell enhancement of carcinoma cell migration. SMAD7 might represent a target for inhibition of IL-1a induced tumor stroma interactions.