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Published on: March 7, 2025
Molecular pathways: cbl proteins in tumorigenesis and antitumor immunity-opportunities for cancer treatment
Mariya S Liyasova1, Ke Ma1, Stanley Lipkowitz2
1Women's Malignancies Branch, Center for Cancer Research, National Cancer Institute, National Institutes of Health, Bethesda, Maryland.
Abstract:
The Cbl proteins are a family of ubiquitin ligases (E3s) that regulate signaling through many tyrosine kinase-dependent pathways. A predominant function is to negatively regulate receptor tyrosine kinase (RTK) signaling by ubiquitination of active RTKs, targeting them for trafficking to the lysosome for degradation. Also, Cbl-mediated ubiquitination can regulate signaling protein function by altered cellular localization of proteins without degradation. In addition to their role as E3s, Cbl proteins play a positive role in signaling by acting as adaptor proteins that can recruit signaling molecules to the active RTKs. Cbl-b, a second family member, negatively regulates the costimulatory pathway of CD8 T cells and also negatively regulates natural killer cell function. The different functions of Cbl proteins and their roles both in the development of cancer and the regulation of immune responses provide multiple therapeutic opportunities. Mutations in Cbl that inactivate the negative E3 function while maintaining the positive adaptor function have been described in approximately 5% of myeloid neoplasms. An improved understanding of how the signaling pathways [e.g., Fms-like tyrosine kinase 3 (Flt3), PI3K, and signal transducer and activator of transcription (Stat)] are dysregulated by these mutations in Cbl has helped to identify potential targets for therapy of myeloid neoplasms. Conversely, the loss of Cbl-b leads to increased adaptive and innate antitumor immunity, suggesting that inhibiting Cbl-b may be a means to increase antitumor immunity across a wide variety of tumors. Thus, targeting the pathways regulated by Cbl proteins may provide attractive opportunities for treating cancer.
Insights
Cbl proteins are ubiquitin ligases regulating tyrosine kinase signaling. Targeting Cbl pathways offers therapeutic opportunities for myeloid neoplasms and increasing antitumor immunity.
Area of Science:
- Biochemistry
- Molecular Biology
- Immunology
Background:
- Cbl proteins function as ubiquitin ligases (E3s) regulating receptor tyrosine kinase (RTK) signaling pathways.
- They target active RTKs for lysosomal degradation, controlling signaling duration and intensity.
- Cbl proteins also act as adaptors, positively influencing signaling by recruiting molecules to RTKs.
Purpose of the Study:
- To explore the multifaceted roles of Cbl proteins in cellular signaling and their therapeutic potential in cancer.
- To investigate how Cbl mutations impact signaling pathways in myeloid neoplasms.
- To evaluate the potential of Cbl-b inhibition for enhancing antitumor immunity.
Main Methods:
- The study reviews existing literature on Cbl protein functions, signaling pathways, and their roles in cancer and immunity.
- It analyzes the impact of specific Cbl mutations on Fms-like tyrosine kinase 3 (Flt3), PI3K, and signal transducer and activator of transcription (Stat) pathways.
- It discusses the implications of Cbl-b's role in immune regulation for cancer immunotherapy.
Main Results:
- Mutations in Cbl proteins are found in approximately 5% of myeloid neoplasms, often inactivating their negative E3 ligase function while preserving adaptor functions.
- Dysregulation of Flt3, PI3K, and Stat pathways by these Cbl mutations provides insights into potential therapeutic targets for myeloid neoplasms.
- Loss of Cbl-b function enhances both adaptive and innate antitumor immunity, suggesting its inhibition as a strategy to boost anti-cancer responses.
Conclusions:
- Cbl proteins are critical regulators of diverse signaling pathways with significant implications in cancer development and immune responses.
- Targeting Cbl-mediated signaling pathways presents promising therapeutic avenues for myeloid neoplasms and various other cancers.
- Inhibiting Cbl-b represents a potential strategy to augment the efficacy of cancer immunotherapies.
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