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Involvement of the 24-kDa cap-binding protein in regulation of protein synthesis in mitosis
Abstract:
The rate of protein synthesis in metaphase-arrested cells is reduced as compared to interphase cells. The reduction occurs at the translation initiation step. Here, we show that, whereas poliovirus RNA translation is not affected by the mitotic translational block, the translation of vesicular stomatitis virus mRNAs is. In an attempt to elucidate the mechanism by which initiation of protein synthesis is reduced in mitotic cells, we found that the interaction of the mRNA 24-kDa cap-binding protein (CBP) with the mRNA 5' cap structure is reduced in mitotic cell extracts, consistent with their lower translational efficiency. Addition of cap-binding protein complex stimulated the translation of endogenous mRNA in extracts from mitotic but not interphase cells. In addition, we found that the 24-kDa CBP from mitotic cells was metabolically labeled with 32P to a lesser extent than the protein purified from interphase cells. These results are consistent with a hypothesis that the 24-kDa CBP is implicated in the inhibition of protein synthesis in metaphase-arrested cells. Possible mechanisms for this inhibition are offered.
Insights
Protein synthesis slows in dividing cells due to impaired translation initiation. A key protein, cap-binding protein (CBP), shows reduced mRNA interaction, explaining this mitotic translational block.
Area of Science:
- Molecular Biology
- Cell Biology
- Biochemistry
Background:
- Protein synthesis rates differ between interphase and metaphase-arrested cells.
- This difference is primarily due to regulation at the translation initiation step.
Purpose of the Study:
- To investigate the mechanism behind reduced protein synthesis initiation in mitotic cells.
- To identify key factors involved in the translational block during metaphase.
Main Methods:
- Analysis of mRNA translation efficiency for different viruses (poliovirus, vesicular stomatitis virus) in mitotic vs. interphase cell extracts.
- Assessing the interaction between the 24-kDa cap-binding protein (CBP) and mRNA 5' cap structures.
- Investigating the metabolic labeling (32P) of CBP in mitotic and interphase cells.
Main Results:
- Vesicular stomatitis virus mRNA translation is inhibited in mitotic cells, unlike poliovirus RNA.
- The interaction of 24-kDa CBP with mRNA 5' cap structures is reduced in mitotic cell extracts.
- Addition of CBP complex enhances endogenous mRNA translation in mitotic extracts.
- Mitotic CBP exhibits lower 32P metabolic labeling compared to interphase CBP.
Conclusions:
- The 24-kDa cap-binding protein (CBP) is implicated in the inhibition of protein synthesis during metaphase arrest.
- Reduced CBP interaction with mRNA caps contributes to the observed translational block in dividing cells.