PTPN18 protein tyrosine phosphatase (BDP1) binds ERBB2, activated in response to EGF stimulation, via PEST and catalytic domains of PTPN18 (Wang et al. 2014).
Protein tyrosine kinase PTPN18 dephosphorylates ERBB2, activated in response to EGF stimulation (Gensler et al. 2004), at tyrosine residues Y1196, Y1112 and Y1248 (Wang et al. 2014). PTPN18 does not dephosphorylate activated EGFR. Dephosphorylation of ERBB2 tyrosines Y1196 and Y1248 attenuates downstream activation of PI3K/AKT and RAS signaling. Dephosphorylation of Y1112 interferes with the recruitment of CBL E3 ubiquitin ligase to activated ERBB2 and CBL-mediated lysosomal route of ERBB2 down-regulation. When phosphorylated by an unknown serine/threonine kinase in an AKT-dependent manner on serine residues S419 and S423, PTPN18 recruits beta-TRCP ubiquitin ligase complex to ERBB2, thus promoting proteasome-dependent ERBB2 degradation (Wang et al. 2014).
Signaling by ERBB2 can be downregulated by ubiquitination and subsequent proteasome-dependent degradation of ERBB2 or activated ERBB2 heterodimers. In addition, protein tyrosine phosphatases that dephosphorylate tyrosine residues in the C-terminus of ERBB2 prevent the recruitment of adapter proteins involved in signal transduction, thus attenuating ERBB2 signaling. STUB1 (CHIP) and CUL5 are E3 ubiquitin ligases that can target non-activated ERBB2 for proteasome-dependent degradation (Xu et al. 2002, Ehrlich et al. 2009). RNF41 (NRDP1) is an E3 ubiquitin ligase that targets ERBB3 and activated heterodimers of ERBB2 and ERBB3 for proteasome-dependent degradation by ubiquitinating ERBB3 (Cao et al. 2007). Two protein tyrosine phosphatases of the PEST family, PTPN12 and PTPN18, dephosphorylate tyrosine residues in the C-terminus of ERBB2, thus preventing signal transduction to RAS and PI3K effectors (Sun et al. 2011, Wang et al. 2014).