Figure 1

Proposed mechanisms for the ligand-induced activation of ErbB1, -2, and -3 and a model for the inhibitory mechanism of Necl-4 for the HRG-induced activation of the ErbB2-ErbB3 signalling. (a) Proposed mechanism for the EGF-induced formation of the ErbB1-ErbB1 homo-dimer. (b) Proposed mechanism for the HRG-induced formation of the ErbB2-ErbB3 hetero-dimer. (c) A model for the inhibitory mechanism of Necl-4 for the HRG-induced formation of the ErbB2-ErbB3 hetero-dimer. In the absence of HRG, the third Ig-like domain of Necl-4 interacts with the domain 3 of the ‘tethered’ form of ErbB3. This interaction inhibits the HRG-induced formation of the ErbB2-ErbB3 hetero-dimer. (d) A model for the activation of the ErbB2-ErbB3 signalling in cancer cells. In cancer cells, Necl-4 is down-regulated or dys-functioned and the inhibitory role of Necl-4 in the HRG-induced formation of the ErbB2-ErbB3 hetero-dimer could be lost and induce cell movement and survival.