Paradoxical cross-talk between the Stat3 and MAPK pathways in CCL25-CCR9 mediated pancreatic cancer growth and proliferation.

Abstract

231 Background: Chemokine receptors have been shown to regulate the progression of several malignancies. Signal transducer and activator of transcription 3 (Stat3) may contribute to the invasive phenotype of several human cancers, but its upstream signals have not been well characterized. Our objective was to investigate the relationship between the CCL25-CCR9 axis and Stat3 signaling in pancreatic cancer cells. Methods: We exposed two established human pancreatic cancer cell lines PANC-1 and MIAPaCa-2 to the cytokine CCL25 (800 ug/uL for 20 min) and measured the activation of Stat3 (phosho-Stat3) by Western blot assay. Stattic, a small molecule Stat3 inhibitor, was used (20uM) to antagonize Stat3 signaling. We also measured activation level of extracellular signal-regulated kinase (phospho-ERK) following CCL25 exposure and used UO126 (10uM), a small molecule MEK inhibitor, to antagonize the MAPK pathway. Changes in cell proliferation were measured by CellTiter Glo Fluorescence assay. Results: Constitutive phosphorylation of Stat3 was observed in both pancreatic cancer cell lines. Exposure of MIAPaCa-2 to CCL25 further increased phospho-Stat3 levels on Western blot assay. We also observed a concomitant increase in phospho-ERK levels with exposure to CCL25 in both cell lines. Exposure of pancreatic cancer cells to CCL25 significantly increased cell proliferation. To determine the mechanism of CCR9-mediated cell proliferation, we used stattic and UO126 to specifically inhibit Stat3 and MEK activation, respectively. Interestingly, pre-treatment with stattic prior to CCL25 exposure resulted in a paradoxical enhancement of phospho-ERK levels. Conversely, inhibition of the MAPK pathway with UO126 led to a paradoxical enhancement of phospho-Stat3 levels. Conclusions: Our results demonstrate that CCL25 activates Stat3 and MAPK pathways to contribute to pancreatic cancer proliferation. We also show potential cross-talk between Stat3 and MAPK pathways, wherein antagonism of one pathway resulted in paradoxical activation of the other pathway. Our findings suggest that therapeutic targeting of downstream pathways may require a multi-drug approach.