A chimeric, ligand-binding v-erbB/EGF receptor retains transforming potential

Area of Science:

• Molecular Biology
• Oncology
• Cell Biology

Background:

• The avian erythroblastosis virus erbB oncogene product (v-erbB) is structurally similar to a truncated form of the human epidermal growth factor (EGF) receptor.
• Both proteins are transmembrane tyrosine kinases, but v-erbB lacks significant portions of the extracellular ligand-binding domain found in the human EGF receptor.

Purpose of the Study:

• To investigate the proposed origin of v-erbB as a truncated avian EGF receptor.
• To determine the functional importance of the deleted extracellular sequences in v-erbB's transforming activity.

Main Methods:

• Construction of a chimeric gene encoding the extracellular and transmembrane domains of the human EGF receptor fused to the cytoplasmic domain of the avian erbB oncogene product.
• Expression of the chimeric gene (HER-erbB) in Rat1 fibroblasts to assess its cellular localization, ligand binding, and signaling capabilities.

Main Results:

• The HER-erbB chimera was successfully transported to the cell surface and bound EGF.
• Ligand binding stimulated the autophosphorylation activity of the chimeric receptor.
• Expression of HER-erbB induced anchorage-independent cell growth and EGF-dependent focus formation in Rat1 cells, indicating transforming potential.

Conclusions:

• The v-erbB oncogene product retains its transforming activity when its cytoplasmic domain is associated with the extracellular ligand-binding domain of the human EGF receptor.
• This suggests that the v-erbB sequences themselves possess oncogenic potential, which can be activated by the human EGF receptor's extracellular domain.