Heparin-binding epidermal growth factor-like growth factor eliminates constraints on activated Kras to promote rapid onset of pancreatic neoplasia.

Pancreatic cancer remains as one of the most deadly cancers with few treatment options at late stages and little information about how it develops through earlier stages. Activating mutation of the Kras gene has been implicated in, but is not sufficient for, tumorigenesis. In mouse models of pancreatic cancer, loss of tumor suppressor genes in conjunction with Kras mutation leads to gradual stochastic acquisition of neoplastic precursors and carcinomas, whereas many cells remain phenotypically unaltered in younger mice. Here, we demonstrate that two oncogenic events, mutation of Kras and production of the growth factor heparin-binding epidermal growth factor-like growth factor (HB-EGF), are sufficient for rapid and complete neoplastic transformation of the exocrine pancreas. We found that macrophages are the major source of HB-EGF production in pancreatic cancer tissue samples, and that macrophages are present in high density and in close association with human pancreatic cancer lesions. In a mouse model, high macrophage density was observed at the earliest stages of neoplastic transformation. The consequence of elevated HB-EGF signaling was investigated without the confounding effects of other macrophage-produced factors via transgenic overexpression of the active form of HB-EGF. In this model, HB-EGF was sufficient to promote Kras-initiated tumorigenesis, inducing rapid and complete neoplastic transformation of the entire exocrine pancreas shortly after birth. HB-EGF overexpression and Kras(G12D) together, but neither alone, increased proliferation with increased cyclinD1 and decreased Cdkn2a/2d (p16/p19(Ink4A/Arf)). These findings establish the importance of oncogenic synergy in cancer initiation and promotion, and establish a molecular link between inflammation and the earliest stages of tumor induction.

Induction of cPLA2 in lung epithelial cells and non-small cell lung cancer is mediated by Sp1 and c-Jun.

Activating mutations in ras genes are frequently associated with non-small cell lung cancer cells (NSCLC) and contribute to transformed growth in these cells. Expression of oncogenic forms of Ras in these cells is associated with increased expression and activity of cytosolic phospholipase A(2) (cPLA(2)) and cyclooxygenase-2 (COX-2), leading to constitutively elevated levels of prostaglandin production. Expression of oncogenic Ras is sufficient to induce these enzymes in normal lung epithelial cells. We have previously reported that the JNK and ERK pathways are necessary for induction of cPLA(2) and have defined a minimal region of the cPLA(2) promoter from -58 to -12 that is required for Ha-Ras-mediated induction. To further characterize the cis-regulatory elements within this region involved in this response, site-directed mutagenesis was used to make mutations at various sites. Three cis-regulatory elements were identified: regions -21/-18, -37/-30, and -55/-53. Mutations in any of these elements decreased basal and Ha-Ras-induced cPLA(2) promoter activity in both normal lung epithelial cells, as well as steady state promoter activity in A549 cells, with a mutation in element -21/-18 completely eliminating all promoter activity. Overexpression studies and gel shift assays indicated that Sp1 may serve as a transcription factor functionally regulating promoter activity by directly interacting with two of the cis-regulatory elements, -21/-18 and -37/-30. Expression of Ha-Ras led to induction of c-Jun protein, which showed functional cooperation with Sp1 in driving promoter activity. Additional unidentified transcription factors bound to the regions from -55/-53 and -37/-34.