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Differential signaling by an anti-p185(HER2) antibody and heregulin
X F Le1, R Vadlamudi, A McWatters
1Department of Experimental Therapeutics, The University of Texas M.D. Anderson Cancer Center, Houston 77030, USA.
Abstract:
To understand the molecular mechanisms by which anti-p185HER2 antibody and the ligand heregulin inhibit tumor growth, we have investigated several signaling proteins and pathways. We report here that anti-p185HER2 monoclonal antibody ID5 induced tyrosine phosphorylation of HER2 in SKBr3 breast cancer cells that overexpress p185HER2. Heregulin beta1 induced phosphorylation of both HER3 and HER2. ID5 produced a greater association of phospholipase C (PLC)-gamma1 with HER2 than did heregulin. Concordantly, ID5, but not heregulin, increased PLC-gamma1 activity. However, the G1 cell cycle arrest and induction of p27Kip1 produced by ID5 were not affected by the inhibition of PLC-gamma. ID5 preferentially induced binding of the Mr 46,000 isoform of SHC to HER2, whereas heregulin preferentially induced binding of the Mr 52,00 isoform of SHC to HER3. Heregulin, but not ID5, induced the p85 subunit of phosphatidylinositol 3'-kinase (PI3-K) to interact with HER3. Heregulin induced sustained activation of P13-K signaling, whereas ID5 had only a transient effect. Heregulin, but not ID5, activated the c-Jun-NH2-terminal kinase cascade. Pretreatment of SKBr3 cells with ID5 decreased heregulin-induced association of HER2 with HER3 as well as the activation of c-Jun-NH2-terminal kinase and PI3-K activities. Inhibition of the mitogen-activated protein kinase pathway in SKBr3 cells did not affect heregulin-induced G2-M-phase arrest, apoptosis, and differentiation. Heregulin-induced apoptosis could be blocked by inhibition of p70s6k, but not by inhibition of PI3-K. Heregulin-induced differentiation could be eliminated by inhibition of PI3-K. We conclude that ID5 and heregulin signal via different pathways, although both agents can inhibit the clonogenic growth of cells that overexpress HER2.
Insights
Anti-HER2 antibody (ID5) and heregulin utilize distinct molecular pathways to inhibit tumor growth. ID5 activates phospholipase C (PLC) signaling, while heregulin activates phosphatidylinositol 3-kinase (PI3-K) and c-Jun-NH2-terminal kinase (JNK) pathways.
Area of Science:
- Oncology
- Molecular Biology
- Cell Signaling
Background:
- HER2 overexpression is common in breast cancer, driving tumor growth.
- Understanding signaling pathways activated by anti-HER2 therapies is crucial for treatment optimization.
Purpose of the Study:
- To elucidate the distinct molecular mechanisms of tumor growth inhibition by anti-HER2 antibody ID5 and the ligand heregulin.
- To compare the signaling pathways activated by ID5 and heregulin in HER2-overexpressing breast cancer cells.
Main Methods:
- Investigated tyrosine phosphorylation of HER2 and HER3.
- Assessed protein-protein interactions including phospholipase C (PLC)-gamma1, SHC isoforms, and phosphatidylinositol 3'-kinase (PI3-K).
- Measured enzyme activities (PLC, PI3-K) and downstream signaling pathway activation (c-Jun-NH2-terminal kinase, mitogen-activated protein kinase).
- Evaluated effects on cell cycle progression (G1, G2-M arrest), apoptosis, and differentiation.
Main Results:
- ID5 induced HER2 phosphorylation and increased PLC-gamma1 association and activity, independent of PLC inhibition for cell cycle arrest.
- Heregulin induced HER2/HER3 phosphorylation and activated PI3-K and c-Jun-NH2-terminal kinase signaling pathways.
- ID5 preferentially bound SHC isoforms to HER2, while heregulin bound SHC to HER3.
- ID5 pretreatment reduced heregulin-induced HER2-HER3 association and downstream signaling.
- Heregulin-induced apoptosis was blocked by p70s6k inhibition, and differentiation by PI3-K inhibition.
Conclusions:
- Anti-HER2 antibody ID5 and heregulin employ divergent intracellular signaling cascades.
- ID5 primarily signals through PLC-gamma1, leading to cell cycle arrest.
- Heregulin signals through PI3-K and JNK pathways, mediating apoptosis and differentiation.
- Both agents effectively inhibit clonogenic growth in HER2-overexpressing cells via distinct mechanisms.