SignalSlide^® Phospho-ErbB Family IHC Controls

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Background

The epidermal growth factor (EGF) receptor is a 170 kDa transmembrane tyrosine kinase that belongs to the HER/ErbB protein family. Ligand binding results in receptor dimerization, autophosphorylation, activation of downstream signaling and lysosomal degradation (1,2). EGFR is phosphorylated on multiple tyrosine residues, each of which leads to activation of a specific downstream pathway. Major residues involved in EGFR signaling include: Tyr845, Tyr992, Tyr1045, Tyr1068, Tyr1148 and Tyr1173 (2-9). Phosphorylation of EGFR at specific serine and threonine residues attenuates EGFR kinase activity. EGFR carboxy-terminal residues Ser1046 and Ser1047 are phosphorylated by CaM kinase II; a mutation to either of these serines results in upregulated EGFR tyrosine autophosphorylation (10).
The ErbB2 (HER2) proto-oncogene encodes a 185 kDa transmembrane, receptor-like glycoprotein with intrinsic tyrosine kinase activity (11). While ErbB2 lacks an identified ligand, ErbB2 kinase activity can be activated in the absence of a ligand when overexpressed and through heteromeric associations with other ErbB family members (12). Amplification of the ErbB2 gene and overexpression of its product are detected in almost 40% of human breast cancers, making it a key therapeutic target (13). ErbB2 has several key residues that are phosphorylated upon its activation including Tyr877, Tyr1221/1222 and Tyr1248 (11,14).
HER3/ErbB3 is a member of the ErbB receptor protein tyrosine kinase family that lacks tyrosine kinase activity. Tyrosine phosphorylation of ErbB3 depends on its association with other ErbB tyrosine kinases. Ligand binding promotes formation of a heterodimer containing ErbB3 and another ErbB protein and subsequent tyrosine phosphorylation of ErbB3 by the activated ErbB kinase (15,16). At least nine putative carboxy-terminal tail tyrosine phosphorylation sites are found in ErbB3, including Tyr1222 and Tyr1289 (17). ErbB3 may function as an oncogenic unit together with other ErbB members in tumor development; ErbB2 requires ErbB3 to drive breast tumor cell proliferation (18). A novel anti-tumor strategy involves inhibiting the interaction between ErbB3 and ErbB tyrosine kinases.