A conditionally active v -ErbB transforms hematopoietic cells to cytokine -independence and promotes cell survival and proliferatio

The purpose of this dissertation is to examine epidermal growth factor receptor (EGFR) signaling using a conditionally active form of the EGFR called v-ErbB:ER. Dysregulation of EGFR signaling occurs in non-small cell lung carcinoma, breast, prostate, pancreatic, colorectal, and many other forms of cancer. The avian oncogene v-ErbB is a homolog to mammalian EGFR. Previous experiments have shown that v-ErbB can transform NIH-3T3 cells to an oncogenic phenotype when expressed in these cells. A conditionally active form of the v-ErbB oncogene was constructed by fusing the hormone-binding portion of the estrogen receptor to the C-terminal domain of v-ErbB. These experiments show that the v-ErbB:ER chimera is dependent upon estrogen or 4-OH tamoxifen for activation. When v-ErbB:ER is expressed in hematopoietic cells it is capable of transforming these cells to cytokine independence. It was also shown that v-ErbB:ER activates the Raf/MEK/ERK and PI3K/Akt pathways as well as JNK and STAT. Activation of v-ErbB:ER leads to phosphorylation and inactivation of the phosphatase PTEN. Hematopoietic cells grown in response to v-ErbB were more resistant to the induction of apoptosis by the MEK inhibitor U0126 and the PI3K inhibitor LY294002 than when grown in the presence of IL-3. In contrast, cells grown in response to v-ErbB were much more sensitive to the induction of apoptosis by the EGFR inhibitor AG1478 than when grown in the presence of IL-3. Transformation by v-ErbB occurs without the production of autocrine growth factors. Finally, it was shown that epidermal growth factor (EGF) stimulates proliferation of hematopoietic cells, EGF enhances IL-3 induced proliferation, and these cells express low levels of EGFR. These studies have led to a better understanding of the interaction between the Raf/MEK/ERK and PI3K/Akt pathways and how these pathways work together to relieve cytokine dependence in hematopoietic cells. This work has led to a better understanding of v-ErbB signaling and cell transformation by dysregulation of this receptor. These studies suggest that it may be possible to use chemotherapy to selectively target cancer cells in patients that have been transformed by EGFR to undergo apoptosis by treating these patients with the EGFR inhibitor.