Integrin-mediated laminin-1 adhesion upregulates CXCR4 and IL-8 expression in pancreatic cancer cells

Pancreatic adenocarcinoma is characterized by a hallmark desmoplastic response that includes extensive proliferation of stromal fibroblasts and deposition of extracellular matrix (ECM).1 The ECM, interacting with cells through cell adhesion receptors, in particular the integrins, has been shown to be a critical regulator of important cell processes such as angiogenesis, mitogenesis, migration, and differentiation.2 We have shown recently in two-and three-dimensional in vitro models that α2β1 integrin-mediated adhesion of pancreatic cancer cell lines to type I collagen, shown to be highly upregulated in pancreatic adenocarcinoma,3-10 up-regulates cell proliferation and haptokinetic migration, a measure of an ECM protein’s inherent ability to promote cell movement in the absence of a chemotactic gradient.11-15 These results support the involvement of α2β1 integrin-mediated adhesion to type I collagen in the generation of the malignant phenotype in pancreatic cancer. Similarly, several recent independent studies have also shown in vitro and in vivo that pancreatic cancer cells stimulate increased expression of type I collagen in pancreatic stellate cells and that this increased type I collagen expression promotes the malignant phenotype in cancer cells as defined by increased proliferation, resistance to chemically-induced apoptosis, and tumorigenesis.16,17 It has also been reported, however, that the α6β1 integrin is overexpressed in pancreatic cancer in vivo,3-6,8 and that α6β1 integrin binding to Ln-1 plays an important role in pancreatic cancer metastasis formation both in vitro and in vivo.18 As part of our recent studies examining the role of the ECM in the promotion of the malignant phenotype in pancreatic cancer, we identified 2 distinct subsets of pancreatic cancer cell lines; those more undifferentiated, including MiaPaCa-2, AsPC-1 and Panc-1, that exhibit maximal haptokinesis on Ln-1; and those more differentiated, including FG, Colo-357, CFPAC, Capan-1, and BxPC-3, that migrate maximally on type I collagen.11 The mechanisms regulating these 2 distinct pancreatic cancer cell phenotypes and their relevance in vivo are unclear. Chemokines are members of the small molecule chemoattractant cytokine family that interact with target cells through G-protein-coupled receptors, designated CXCR or CCR, corresponding to their chemokine ligands.19 CXCR4 in particular, whose ligand is SDF-1, has been shown to be upregulated in several types of cancer, including oral squamous cell carcinoma, breast, ovary, prostate, kidney, brain, lung, thyroid, and pancreas.20-23 This up-regulated CXCR4 chemokine receptor expression in pancreatic cancer is associated with increased cell survival, proliferation, migration, invasion, and metastasis. IL-8 belongs to the superfamily of CXC chemokines with known proinflammatory effects.24 IL-8 has been shown to be upregulated in response to TGFβ1 signaling25 and to be expressed in pancreatic cancer, also correlating with increased tumorigenic and metastatic potential.24,26 We have shown recently in multiple pancreatic cancer cell lines that adhesion to Fn upregulates whereas adhesion to type I collagen downregulates IL-8 expression in vitro.12,14 In the present study, we examined the potential of the ECM to regulate the expression of CXCR4 and IL-8 in 8 pancreatic cancer cell lines derived from all 3 tumor histological grades and from both primary and metastatic lesions. Our results indicate that CXCR4 protein is expressed to varying degrees by all cell lines tested. The highly undifferentiated MiaPaCa-2 cell line, expressing the lowest levels of CXCR4 and showing maximal α6β1 and α3β1 integrin-mediated migration on Ln-1, could be induced to upregulate CXCR4 expression significantly after growth on Ln-1. CXCR4 expression seemed to be regulated, at least in part, by the α6β1 integrin. By contrast, IL-8 cytokine expression was also upregulated after growth of MiaPaCa-2 cells on Ln-1, but both the α3β1 and α3β1 integrins seem to play regulatory roles in the expression of this cytokine. These data indicate that integrin-mediated upregulation of CXCR4 and IL-8 expression on Ln-1 in pancreatic cancer cells occurs through distinct mechanisms and may play a role in pancreatic cancer metastasis.