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MEKK1 induces c-Jun complexes that act as negative regulators for cell survival and proliferation of HCC cells
Fumitake Komoda1, Yuji Shino, Tatsuya Hirano
1Department of Medicine and Clinical Oncology (K1), Graduate School of Medicine, Chiba University, 1-8-1 Inohana, Chuou-ku, Chiba 260-8670, Japan.
Abstract:
c-Jun has a variety of functions including proliferation, differentiation and death. c-Jun is specifically phosphorylated by c-Jun N-terminal kinase (JNK) which is regulated by Ras-MEKK1-MKK4/7 pathway. Previous studies showed that c-Jun protein plays a positive role in cell proliferation of normal hepatocytes and was detected in hepatocellular carcinoma (HCC) tissues. However, the function of c-Jun in HCC cells has not been examined. The aim of this study was to investigate whether the MEKK1-JNK signaling pathway and c-Jun may be involved in the survival and proliferation of HCC. Surprisingly, an active not dominant negative form of MEKK1 (CA-MEKK1) remarkably inhibited the colony formation of HCC cells. Gel retardation assays indicated that CA-MEKK1 induces c-Jun DNA binding, and luciferase assays exhibited that CA-MEKK1 enhances the transactivating activity of c-Jun in HCC cells. These results suggested that the inhibitory effect of CA-MEKK1 on colony formation is likely to be mediated by c-Jun. As expected, when wild-type c-Jun was transfected, the colony formation was significantly reduced. Especially in HuH7 cells, c-Jun transfected cells failed to make any colonies. Our data suggested that c-Jun activation can induce negative effect on survival and proliferation of HCC cells.
Insights
Activating the MEKK1-JNK pathway surprisingly inhibits hepatocellular carcinoma (HCC) cell growth. This pathway activation enhances c-Jun DNA binding and activity, leading to reduced HCC cell survival and proliferation.
Area of Science:
- Oncology
- Molecular Biology
- Cell Signaling
Background:
- c-Jun protein regulates cell proliferation, differentiation, and death.
- c-Jun is phosphorylated by c-Jun N-terminal kinase (JNK), part of the Ras-MEKK1-MKK4/7 pathway.
- c-Jun is detected in hepatocellular carcinoma (HCC) tissues, but its role in HCC cells is unclear.
Purpose of the Study:
- To investigate the involvement of the MEKK1-JNK signaling pathway and c-Jun in HCC cell survival and proliferation.
Main Methods:
- Transfection with an active MEKK1 mutant (CA-MEKK1).
- Gel retardation assays to assess c-Jun DNA binding.
- Luciferase assays to measure c-Jun transactivating activity.
- Transfection with wild-type c-Jun.
Main Results:
- CA-MEKK1 significantly inhibited HCC cell colony formation.
- CA-MEKK1 increased c-Jun DNA binding and transactivating activity.
- Overexpression of wild-type c-Jun also significantly reduced colony formation, particularly in HuH7 cells.
Conclusions:
- Activation of the MEKK1-JNK pathway, leading to increased c-Jun activity, negatively impacts HCC cell survival and proliferation.
- c-Jun activation may serve as a therapeutic target for hepatocellular carcinoma.