Abstract
Neurotensin (NT) stimulates protein kinase D1 (PKD1), extracellular signal regulated kinase (ERK), c‐Jun N‐terminal Kinase (JNK), and DNA synthesis in the human pancreatic adenocarcinoma cell line PANC‐1. To determine the effect of PKD1 overexpression on these biological responses, we generated inducible stable PANC‐1 clones that express wild‐type (WT) or kinase‐dead (K618N) forms of PKD1 in response to the ecdysone analog ponasterone‐A (PonA). NT potently stimulated c‐Jun Ser^63^ phosphorylation in both wild type and clonal derivatives of PANC‐1 cells. PonA‐induced expression of WT, but not K618N PKD1, rapidly blocked NT‐mediated c‐Jun Ser^63^ phosphorylation either at the level of or upstream of MKK4, a dual‐specificity kinase that leads to JNK activation. This is the first demonstration that PKD1 suppresses NT‐induced JNK/cJun activation in PANC‐1 cells. In contrast, PKD1 overexpression markedly increased the duration of NT‐induced ERK activation in these cells. The reciprocal influence of PKD1 signaling on pro‐mitogenicERK and pro‐apopotic JNK/c‐Jun pathways prompted us to examine whether PKD1 overexpression promotes DNA synthesis and proliferation of PANC‐1 cells. Our results show that PKD1 overexpression increased DNA synthesis and cell numbers of PANC‐1 cells cultured in regular dishes or in polyhydroxyethylmethacrylate [Poly‐(HEMA)]‐coated dishes to eliminate cell adhesion (anchorage‐independent growth). Furthermore, PKD1 overexpression markedly enhanced DNA synthesis induced by NT (1–10 nM). These results indicate that PKD1 mediates mitogenic signaling in PANC‐1 and suggests that this enzyme could be a novel target for the development of therapeutic drugs that restrict the proliferation of these cells. J. Cell. Physiol. 223: 309–316, 2010. © 2010 Wiley‐Liss, Inc.