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Updated: Mar 31, 2026
Experimental Approaches to Study Mitochondrial Localization and Function of a Nuclear Cell Cycle Kinase, Cdk1
Published on: February 25, 2016
MAPK1 phosphorylates CCNB1 at Ser128 to drive mitotic progression and cell proliferation in triple-negative breast
Beinan Han1, Xiangpin Zhu1, Zhiren Han1
1Department of Oncology, Sun Yat-sen Memorial Hospital, Sun Yat-sen University, Guangzhou, China.
Aims:
Triple-negative breast cancer (TNBC) is an aggressive subtype of breast cancer lacking effective targeted therapies. The MAPK pathway is frequently activated in TNBC, but clinical responses to MAPK inhibitors remain limited, largely due to adverse effects and adaptive resistance. MAPK1 (ERK2) is well known to promote tumor progression primarily by phosphorylating transcription factors that regulate gene expression, yet its downstream substrates beyond transcription factors remains poorly defined. Identifying these noncanonical substrates is crucial for uncovering alternative MAPK1-driven oncogenic mechanisms and may reveal therapeutic vulnerabilities to overcome the limitations of MAPK pathway inhibition.
Materials And Methods:
TurboID-based proximity labeling coupled with mass spectrometry was performed in TNBC cells to identify MAPK1-interacting proteins. Biochemical assays, including co-immunoprecipitation and in vitro kinase assays, were performed to confirm MAPK1-substrate interactions. Generation of CCNB1-Ser128 mutants, nuclear-cytoplasmic fractionation, immunofluorescence, cell cycle analysis, and in vivo xenograft experiments were conducted to determine functional consequences.
Key Findings:
Cyclin B1 (CCNB1), a key regulator of early mitotic entry, was identified as a MAPK1-associated protein. MAPK1 phosphorylates CCNB1 at serine 128, and this modification facilitates CCNB1 nuclear translocation and the G2-to-prophase transition. Pharmacological inhibition or genetic depletion of MAPK1 reduced CCNB1 Ser128 phosphorylation and impaired mitotic progression. The phospho-mimetic CCNB1-S128D mutant partially rescued proliferation defects induced by MAPK1 knockdown.
Significance:
These findings expand the functional scope of MAPK1 beyond transcriptional regulation and identify CCNB1 Ser128 phosphorylation as a key effector mechanism linking MAPK signaling to mitotic control in TNBC. The MAPK1-CCNB1 axis may represent a mechanistically informed therapeutic target for TNBC.
Insights
The mitogen-activated protein kinase 1 (MAPK1) pathway regulates cell division in triple-negative breast cancer (TNBC). Researchers found MAPK1 directly phosphorylates Cyclin B1 (CCNB1), impacting cell cycle progression and offering a potential therapeutic target for TNBC.
Area of Science:
- Oncology
- Molecular Biology
- Cell Biology
Background:
- Triple-negative breast cancer (TNBC) is an aggressive cancer subtype with limited targeted therapies.
- The MAPK pathway is often activated in TNBC, but MAPK inhibitors have shown limited clinical efficacy due to resistance and side effects.
- MAPK1 (ERK2) is known to drive tumor progression, but its non-transcriptional targets are not well understood, hindering the development of effective treatments.
Purpose of the Study:
- To identify novel, non-transcriptional substrates of MAPK1 in TNBC.
- To investigate the functional role of MAPK1-mediated phosphorylation of identified substrates in TNBC progression.
- To explore the potential of targeting the MAPK1 signaling axis for TNBC therapy.
Main Methods:
- Utilized TurboID proximity labeling and mass spectrometry to identify MAPK1-interacting proteins in TNBC cells.
- Performed biochemical assays (co-immunoprecipitation, in vitro kinase assays) to validate MAPK1-CCNB1 interactions.
- Conducted experiments including mutant generation, cell fractionation, immunofluorescence, cell cycle analysis, and xenograft studies to assess functional impacts.
Main Results:
- Identified Cyclin B1 (CCNB1), a key cell cycle regulator, as a novel MAPK1-associated protein.
- Demonstrated that MAPK1 directly phosphorylates CCNB1 at serine 128 (S128).
- Showed that MAPK1-mediated CCNB1 phosphorylation promotes nuclear translocation and mitotic entry, and that inhibiting MAPK1 impairs this process.
Conclusions:
- MAPK1's function extends beyond transcriptional regulation, directly impacting mitotic control through CCNB1 phosphorylation.
- The phosphorylation of CCNB1 at S128 by MAPK1 is a critical mechanism linking MAPK signaling to cell cycle progression in TNBC.
- The identified MAPK1-CCNB1 axis represents a promising, mechanistically informed therapeutic target for treating triple-negative breast cancer.
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