Activation of different signaling pathways in the regulation of biological properties of human pancreatic cancer cells by the mucin MUC4 and the oncogenic receptor ErbB2 genes

The mucin MUC4 and its membrane partner the ErbB2 oncogenic receptor are potential actors and partners in pancreatic tumourigenesis. However, the way they function is still largely unknown. We thus undertook in this work to identify the cellular mechanisms and the intracellular signalling pathways under the control of both ErbB2 and MUC4. Using co-immunoprecipitation, we show that MUC4 and ErbB2 interact in the human pancreatic adenocarcinomatous cell line CAPAN-2. Stable Knocked-Down (KD) cellular clones for both MUC4 and ErbB2 were raised by a shRNA approach. Biological properties of these cells were then studied in vitro and in vivo. Our results show that ErbB2-KD cells are more apoptotic and less proliferative (decreased cyclin D1 and increased p27kip1 expression) while migration and invasive properties were not altered. MUC4-KD clones were less proliferative with decreased cyclin D1 expression, G1 cell cycle arrest and altered ErbB2/ErbB3 expression. Their migration properties were reduced whereas invasive properties were increased. Importantly, inhibition of ErbB2 and MUC4 expression did not impair the same signalling pathways (inhibition of MUC4 expression affected the JNK pathway whereas that of ErbB2 altered the MAPK pathway). Finally, ErbB2-KD and MUC4-KD cells showed impaired tumour growth in vivo. This indicates that ErbB2 and MUC4, that physically interact, activate different intracellular signalling pathways to regulate biological properties of pancreatic cancer cells. Altogether, these data bring new information regarding molecular mechanisms under the control of both MUC4 and ErbB2 that will have to be taken into account for developing efficient targeting of both proteins in order to slow down/stop pancreatic tumourigenesis. profiling of pancreatic cells depleted for ErbB2 and MUC4