Xu Li, Xianjue Ma, and Lianfeng Wu’s research groups at the School of Life Sciences, published a paper in Developmental Cell , entitled “Low-density Lipoprotein Receptor-related Protein 1 Mediates Notch Pathway Activation”. Collaborating with Wenqi Wang at UC Irvine and Junjie Chen at MD Anderson Cancer Center, this research established the human Notch pathway protein interaction network, and discovered many key regulators including low-density-lipoprotein-receptor-related protein 1 (LRP1). Their findings shed lights on LRP1's potential role as a therapeutic target for Notch-related cancers.

Weixiang Bian, Mengfan Tang, Hua Jiang, Wenyan Xu, Wanyu Hao and Yue Sui are the co-first authors. Xu Li, Wenqi Wang, Junjie Chen, Xianjue Ma and Lianfeng Wu are the co-corresponding authors. 

The team first constructed stable cell lines containing 13 core proteins of the Notch signaling pathway (NOTCH1/2/3/4, MAML1/2/3, JAG1/2, DLL1/3/4, RBPJ) in human cells. The protein complexes associated with 13 core components of Notch pathway were identified by tandem affinity purification mass spectrometry. Subsequently, the team identified a number of high-confidence interacting proteins using bioinformatics analysis, and established a protein interaction network of the human Notch signaling pathway, which greatly expanded the current understanding of the Notch signaling pathway.

By integrating the Notch pathway protein interaction network with multiple databases related to human disease, the team found that LRP1 might be an important regulator of Notch signaling. LRP1 not only binds to the Notch ligand Delta, but Westlake University Researchers Established the Human Notch Pathway Protein Interaction Network and Indentified Potential Drug Targets for Notch-related Diseases also has mutations and abnormal expression in congenital heart disease, acute T lymphoblastic leukemia (T-ALL) and squamous cell carcinoma (SCC) associated with Notch disorders, suggesting that LRP1 may be involved in the regulation of Notch signaling pathway.

Subsequently, the team conducted a series of biochemical and cellular experiments to confirm that LRP1 is a key upstream regulator of the Notch pathway. LRP1 interacts with Notch ligand Delta to influence its binding to ubiquitin ligase E3, which in turn contributes to changes in Notch ligand Delta ubiquitin chain, thus mediating endocytic recycle, membrane localization and stability of Delta. In order to further demonstrate the importance of LRP1 in the Notch signaling pathway, the team employed additional two model organisms, C. elegans and Drosophila, to further explore the function of LRP1, and confirmed that LRP1 is involved in the activation of Notch signaling pathway. Finally, to determine the biological significance of LRP1 under pathological conditions, they constructed a mouse xenograft tumor and tail vein injection T-ALL model, and found that LRP1 knockout significantly inhibited leukemia cell migration, invasion and tumorigenesis. RAPm6, an antagonist of LRP1, can effectively inhibit Notch signaling and significantly slow down tumor progression. 

In conclusion, the team established the protein interaction network of human Notch signaling pathway, identified LRP1, a key upstream regulator of Notch signaling pathway, and revealed that LRP1 may serve as a potential therapeutic target for Notch related diseases.

Image: (left) Important proteins and related functions in the protein interaction network of Notch signaling pathway. (right) Human Notch pathway protein interaction network: Lightning (Notch ligand and receptor binding) between the two planets (cells) triggers the binding of molecules (proteins) on the planet, creates the life