Functional p38 MAPK Identified by Biomarker Profiling of Pancreatic Cancer Restrains Growth through JNK Inhibition and Correlates with Improved Survival

Abstract

Numerous biomarkers for pancreatic cancer have been reported. We determined the extent to which such biomarkers are expressed throughout metastatic progression, including those that effectively predict biologic behavior. Biomarker profiling was performed for 35 oncoproteins in matched primary and metastatic pancreatic cancer tissues from 36 rapid autopsy patients. Proteins of significance were validated by immunolabeling in an independent sample set, and functional studies were performed in vitro and in vivo. Most biomarkers were similarly expressed or lost in expression in most samples analyzed, and the matched primary and metastases from a specific patient were most similar to each other than to other patients. However, a subset of proteins showed extensive interpatient heterogeneity, one of which was p38 MAPK. Strong positive pp38 MAPK immunolabeling was significantly correlated with improved postresection survival by multivariate analysis (median overall survival 27.9 months, P = 0.041). In pancreatic cancer cells, inhibition of functional p38 by SB202190 increased cell proliferation in vitro in both low-serum and low-oxygen conditions. High functional p38 activity in vitro corresponded to lower levels of pJNK protein expression, and p38 inhibition resulted in increased pJNK and pMKK7 by Western blot analysis. Moreover, JNK inhibition by SP600125 or MKK7 siRNA knockdown antagonized the effects of p38 inhibition by SB202190. In vivo, SP600125 significantly decreased growth rates of xenografts with high p38 activity compared with those without p38 expression. Functional p38 MAPK activity contributes to overall survival through JNK signaling, thus providing a rationale for JNK inhibition in pancreatic cancer management.