HEDGEHOG AND ITS PATHWAY MEMBERS ARE MISEXPRESSED AND ACTIVE IN THE MAJORITY OF SPORADIC HUMAN PANCREATIC ADENOCARCINOMAS: A BIOLOGICALLY IMPORTANT PATHWAY AND POTENTIAL THERAPEUTIC TARGET.

Abstract

The Hedgehog (Hh) signaling pathway has been implicated in pancreatic tumorigenesis, where it is believed to play a critical role as both an initiator and maintenance factor. However, the prevalence and magnitude of Hh pathway aberration in sporadic human pancreatic adenocarcinomas remains unknown. Here we present quantitative real-time PCR data from 20 human adenocarcinomas and show increased mRNA expression for 7 representative Hedgehog pathway genes. Methods: Individual samples were obtained from 20 human pancreatic adenocarcinomas freshly resected at our institution. Total RNA was extracted, genomic DNA was removed, and the RNA was subjected to quantitative real-time PCR analysis, using algorithmically generated primers for the genes SHH, IHH, DHH, PTCH, SMO, GLI1, and GLI2. All samples in a given run were normalized to a standardized sample of 18S rRNA, and gene expression levels in tumors were compared to those in an averaged expression level of 10 normal human pancreata. Results: All human tumors showed marked upregulation of the Hedgehog pathway when compared to normal pancreatic controls. All tumors misexpress Hh ligands, principally SHH and IHH (median 168- and 165-fold upregulation, respectively). Furthermore, this pathway is active, as indicated by an impressive upregulation of downstream mediators of the Hh pathway, GLI1 and GLI2 (median 71- and 96-fold). DHH, PTCH, and SMO are identified but demonstrate comparatively less upregulation (median 9-, 2-, and 5-fold). Conclusions: Misexpression of Hh ligands and activation of the Hh pathway is a prevalent finding in human pancreatic adenocarcinoma. The finding that all adenocarcinomas tested to date have an impressive increase in activity suggests that Hh pathway aberration is an important fundamental mechanism in pancreatic tumorigenesis. Thus, inhibition of the Hh pathway may represent a powerful potential treatment modality in pancreatic adenocarcinoma.