In a study to evaluate the molecular interactions critical for oncogenic effects of over expression of the erbB-2 receptor in lung cancer, T antigen immortalized human bronchial epithelial cells were engineered to over express this receptor. Examination of tumorigenic and non-tumorigenic clones suggested the hypothesis that EGFR-erbB-2 heterodimers, formed under the influence of high autocrine production of TGF-alpha, were necessary for tumor formation. This hypothesis was supported by experiments in which a tumorigenic, high TGF-alpha producer, E6T, was transfected with an antisense TGF-alpha construct, creating a cell line, (E6TA), with a 95% reduction in TGF-alpha secretion and loss of tumorigenicity. In order to evaluate heterodimer formation, E6T and E6TA cells were studied for constitutive levels of erbB family receptors (erbB1-4). This study revealed that in this cell type, erbB-1 is the dominant receptor. In addition, it has been shown that, in addition to TGF-alpha, these clones express amphiregulin,betacellulin,HB-EGF,and heregulins alpha 2a and beta3. Studies comparing the activation of signal transduction pathways downstream of these receptors indicate that, with no external growth factor addition, the MAPK and STAT3 pathways are differentially activated in the tumorigenic E6T when compared to E6TA cells. In studies comparing heterodimer formation in these two cells, it was shown that all possible Erb family heterodimers are formed. However,tne ErbB-1/-2 heterodimer is differentially formed in tumorigenic E6T compared to E6TA cells. Endoplasmic reticulum trapping of either ErbB-1 or ErbB-2 was achieved by expression of single chain antibodies carrying an ER trapping signal and specific for either receptor. Tumorigenicity studies on resultant cell clones demonstrated the requirement of both receptors for tumorigenicity and enhanced signal transduction through MAPK and STAT signaling. Requirement of ErbB-1/-2 heterodimer for enhanced signaling was further supported by the use of a tyrphostin inhibitor specific for ErbB-2.1997-10-01 to 1998-07-31 - EGF, erbB Receptor Family, erbB2, Heregulin, Receptor Tyrosine Kinase, - Human Tissues, Fluids, Cells, etc.
