Trastuzumab-induced recruitment of Csk-homologous kinase (CHK) to ErbB2 receptor is associated with ErbB2-Y1248 phosphorylation and ErbB2 degradation to mediate cell growth inhibition

Abstract

The inhibitory effect of trastuzumab, a humanized monoclonal antibody directed against the extracellular domain of ErbB2, is associated with its ability to induce ErbB2-Y1248 phosphorylation, and the status of phosphorylated ErbB2-Y1248 (ErbB2-pY1248) may correlate with the sensitivity of breast cancers to trastuzumab. The mechanisms of which remain unclear. Here, we show that binding of trastuzumab to ErbB2 activates ErbB2 kinase activity and enhances ErbB2-Y1248 phosphorylation in trastuzumab-sensitive breast cancer cells. This in turn increases the interaction between ErbB2 and non-receptor Csk-homologous kinase (CHK), leading to growth inhibition of breast cancer cells. Overexpression of CHK mimics trastuzumab treatment to mediate ErbB2-Y1248 phosphorylation, Akt downregulation, and growth inhibition of trastuzumab-sensitive breast cancer cells. CHK overexpression combined with trastuzumab exerts an additive effect on cell growth inhibition. We further demonstrate that positive ErbB2-pY1248 staining in ErbB2-positive breast cancer biopsies correlates with the increased trastuzumab response in trastuzumab neoadjuvant settings. Collectively, this study highlights an important role for ErbB2-pY1248 in mediating trastuzumab-induced growth inhibition and trastuzumab-induced interactions between CHK and ErbB2-pY1248 is identified as a novel mechanism of action that mediates the growth inhibition of breast cancer cells. The novel mechanistic insights into trastuzumab action revealed by this study may impact the design of next generation of therapeutic monoclonal antibodies targeting receptor tyrosine kinases, as well as open new avenues to identify novel targets for the treatment of ErbB2-positive cancers.

Trastuzumab is not a tyrosine kinase inhibitor

“…Negative signals downstream of ERBB2 subsequently contribute to growth inhibition of ERBB2-positive breast cancer cells. 9,10 Taken together, these studies provide evidence that trastuzumab does not function as a TKI. …”

“…7 Gijsen and co-workers also reported that trastuzumab induced ERBB2 tyrosine phosphorylation, 8 and together with another group observed that trastuzumab treatment induced paradoxical activation of mitogenactivated protein kinase 1/3 in breast cancer cells. 8,9 In 2014, we demonstrated that trastuzumab upregulated ERBB2 tyrosine kinase activity in trastuzumab-sensitive breast cancer cells, and that this upregulated a ctivity contributed to ERBB2 phosphorylation. 9 Despite different effects on ERBB2 phosphorylation, both lapatinib and trastuzumab have the capacity to downregulate Akt activity and to inhibit growth of breast cancer cells.…”

“…8,9 In 2014, we demonstrated that trastuzumab upregulated ERBB2 tyrosine kinase activity in trastuzumab-sensitive breast cancer cells, and that this upregulated a ctivity contributed to ERBB2 phosphorylation. 9 Despite different effects on ERBB2 phosphorylation, both lapatinib and trastuzumab have the capacity to downregulate Akt activity and to inhibit growth of breast cancer cells. Based on our data, we postulate that binding of trastuzumab to ERBB2 could induce structural changes in the ERBB2 cytoplasmic kinase domain, leading to allosteric activation of ERBB2 kinase and trans phosphoryl ation of ERBB2.…”

“…6 Growing evidence indicates that targeting ERBB2 using trastuzumab increases ERBB2 tyrosine phosphorylation in trastuzumab-sensitive breast cancer cells. [7][8][9] Diemeier and colleagues reported that the inhibitory effect of trastuzumab on trastuzumab-sensitive breast…”

“…Based on our data, we postulate that binding of trastuzumab to ERBB2 could induce structural changes in the ERBB2 cytoplasmic kinase domain, leading to allosteric activation of ERBB2 kinase and trans phosphoryl ation of ERBB2. 9,10 Trastuzumab-induced ERBB2 phosphorylation provides docking sites for downstream signalling molecules, which are different from those induced by a ligand (such as epidermal growth factor), in that they recruit signalling molecules such as Csk-homologous kinase, a non-receptor tyrosine kinase. Negative signals downstream of ERBB2 subsequently contribute to growth inhibition of ERBB2-positive breast cancer cells.…”