Expression and regulation of c-ERBB ligands in human head and neck squamous carcinoma cells

We recently reported that multiple c-erbB ligands differentially modulate in vitro proliferation, invasion and expression of matrix metalloproteinases in human head and neck squamous carcinoma cells (HNSCC). In order to evaluate further the importance of c-erbB ligands in tumor progression, the expression and regulation of this growth factor family in HNSCC cells was studied. We demonstrate that mRNAs for the 6 major c-erbB ligands, namely, epidermal growth factor (EGF), transforming growth factor-alpha (TGF-alpha), betacellulin (BTC), heparin-binding epidermal growth factor-like growth factor (HB-EGF), amphiregulin (AR) and heregulin (HRG), are expressed in a large panel of HNSCC cell lines. In addition to TGF-alpha, other ligands (notably BTC and HRG-beta1) are involved in the autocrine growth regulation of these cells. Each c-erbB ligand when applied exogenously, induced mRNA expression of both itself and the remaining family members and a differential response in the kinetics of induction was found. HB-EGF and HRG mRNAs were induced rapidly (within 1 hr) and to a greater extent (3.2-6.2- and 4.8-7. 3-fold increase) than TGF-alpha, BTC and AR mRNAs (1.6-2.7, 1.8-3.6- and 1.6-4.2-fold, respectively). This pattern was observed for all inducing ligands tested. Analysis of mRNA stability, and concurrent treatment with BTC (as an inducing ligand) and cycloheximide (to inhibit protein synthesis) suggested both transcriptional and post-transcriptional regulatory mechanisms. These results support and extend previous observations of c-erbB receptor signaling as a critical element in the pathogenesis and progression of HNSCC, and emphasize the role of autocrine ligand production.