Effectiveness of EGFR/HER2-targeted drugs is influenced by the downstream interaction shifts of PTPIP51 in HER2-amplified breast cancer cells

Abstract

Breast cancer is the most common female cancerous disease and the second most cause of cancer death in women. About 20–30% of these tumors exhibit an amplification of the HER2/ErbB2 receptor, which is coupled to a more aggressive and invasive growth of the cancer cells. Recently developed tyrosine kinase inhibitors and therapeutic antibodies targeting the HER2 receptor improved the overall survival time compared with sole radio- and chemotherapy. Upcoming resistances against the HER2-targeted therapy make a better understanding of the receptor associated downstream pathways an absolute need. In earlier studies, we showed the involvement of Protein Tyrosine Phosphatase Interacting Protein 51 (PTPIP51) in the mitogen-activated protein kinase (MAPK) pathway. The MAPK pathway is one of the most frequently overactivated pathways in HER2-amplified breast cancer cells. This study is aimed to elucidate the effects of four different TKIs on the interactome of PTPIP51, namely with the receptors EGFR and HER2, 14-3-3/Raf1 (MAPK pathway), its regulating enzymes, and the mitochondria-associated interaction partners in HER2 breast cancer cell lines (SK-BR3 and BT474) by using the Duolink proximity ligation assay, immunoblotting and knockdown of PTPIP51. Inhibition of both EGFR and HER2/ErbB2R shifted PTPIP51 into the MAPK pathway, but left the mitochondria-associated interactome of PTPIP51 unattended. Exclusively inhibiting HER2/ErbB2 by Mubritinib did not affect the interaction of PTPIP51 with the MAPK signaling. Selective inhibition of HER2 induced great alterations of mitochondria-associated interactions of PTPIP51, which ultimately led to the most-effective reduction of cell viability of SK-BR3 cells of all tested TKIs. The results clearly reveal the importance of knowing the exact mechanisms of the inhibitors affecting receptor tyrosine kinases in order to develop more efficient anti-HER2-targeted therapies.

PTPIP51 crosslinks the NFκB signaling and the MAPK pathway in SKBR3 cells and provides a bypass mechanism for NFκB inhibition

“…Selective IKK inhibition by IKK-16 enhances the interaction of PTPIP51 and the HER2 receptor ( Fig.3) The amplified HER2 receptor activates the NFκB signaling via the canonical pathway and the activation of IKKα (8). PTPIP51 interacts with the HER2 receptor and seems to be crucial for the responsiveness of HER2 amplified breast cancer cells towards HER2 targeted therapies (14). Thus., we examined the interaction of PTPIP51 and the HER2 receptor under NFκB inhibition.…”

“…Recent studies of our group substantiated an interaction of PTPIP51 and the HER2 receptor. Interestingly, selective inhibition of the HER2 receptor using Mubritinib induced a formation of a ternary complex consisting of PTPIP51, c-Src, and HER2, which potentially depicts a resistance mechanism against HER2 targeted tyrosine kinase inhibitors (14).…”

“…Noteworthy, the scaffold protein Protein Tyrosine Phosphatase Interacting Protein 51 (PTPIP51) interacts with both signaling structures, the HER2 receptor, and the NFκB signaling (13,14). The interaction of PTPIP51 with the HER2 receptor seems crucial for the sensitivity of HER2 amplified breast cancer cell lines to EGFR/HER2 targeted therapies (14). Besides the direct interaction with the HER2 receptor, PTPIP51 is involved in the titration of the MAPK signaling (15)(16)(17).…”

The Importance of the Right Framework: Mitogen-Activated Protein Kinase Pathway and the Scaffolding Protein PTPIP51

“…In Her2 amplified breast cancer cells, the phosphorylation of PTPIP51 at Tyr176 is to a great extend performed by the EGFR. Inhibition of the EGFR in Her2 amplified breast cancer cells induces a reduction of PTPIP51 phosphorylation at the Tyr176 residue accompanied by a formation of the Raf-1/14-3-3β/PTPIP51 interactome, thus proofing a normal regulation of MAPK-related interactions of PTPIP51 [ 50 ].…”

“…Interestingly, PTPIP51 also interacts with the Her2 receptor, but it is not clear if the Her2 receptor phosphorylates PTPIP51 or if PTPIP51 forms a scaffold for the interaction of the Her2 receptor with other signaling molecules [ 50 ]. Of note, selective inhibition of the Her2 receptor with the TKI Mubritinib induces a formation of a potential ternary interactome consisting of the Her2 receptor, PTPIP51 and c-Src [ 50 ]. As mentioned above, c-Src plays a crucial role in Her2 targeted therapy resistance and the transduction of growth and survival signals [ 41 , 42 , 44 , 46 ].…”