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Cytoplasmic microtubules are essential for the formation of membrane-bound polyribosomes
Abstract:
Colchicine, at low intracellular concentrations, causes a rapid depolymerization of membrane-associated polyribosomes. Poly(A+) mRNA is rapidly lost from these polysomes, and 80 S monomers are left attached to the membranes of the endoplasmic reticulum. Binding studies and measurements of intracellular colchicine concentrations indicate that the drug is acting via depolymerization of cytoplasmic microtubules. The vinca alkaloids, vincristine and vinblastine, have the same effect on polyribosomes, whereas lumicolchicine is ineffective. Furthermore, cordycepin and actinomycin D are without effect on polyribosomes indicating that colchicine is not simply inhibiting the production or transport of new mRNA. It appears that disruption of the cytoplasmic microtubule network prevents membrane-associated ribosomes from reinitiating protein synthesis resulting in the rapid loss of mRNA.
Insights
Colchicine rapidly depolymerizes cytoplasmic microtubules, leading to the loss of messenger RNA (mRNA) from membrane-associated polyribosomes. This disruption prevents protein synthesis initiation, highlighting microtubules
Area of Science:
- Molecular Biology
- Cell Biology
- Biochemistry
Background:
- Polyribosomes (polysomes) are crucial for protein synthesis, translating messenger RNA (mRNA) into proteins.
- Cytoplasmic microtubules form the cell's structural network and are involved in various cellular processes.
- Colchicine is a known disruptor of microtubule polymerization.
Purpose of the Study:
- To investigate the effect of colchicine on membrane-associated polyribosomes and mRNA.
- To elucidate the mechanism by which colchicine impacts protein synthesis at the polysome level.
- To determine the role of cytoplasmic microtubules in maintaining mRNA on polysomes.
Main Methods:
- Treatment of cells with colchicine and related compounds (vinca alkaloids, lumicolchicine, cordycepin, actinomycin D).
- Analysis of polyribosome structure and mRNA content.
- Measurement of intracellular colchicine concentrations and binding studies.
Main Results:
- Low intracellular concentrations of colchicine rapidly depolymerized membrane-associated polyribosomes.
- Poly(A+) mRNA was rapidly lost from these polysomes, leaving 80 S monomers attached to endoplasmic reticulum membranes.
- Vinca alkaloids mimicked this effect, while lumicolchicine, cordycepin, and actinomycin D did not.
Conclusions:
- Colchicine disrupts protein synthesis by depolymerizing cytoplasmic microtubules, which are essential for maintaining mRNA on polysomes.
- The disruption of the microtubule network prevents the reinitiation of protein synthesis on membrane-associated ribosomes.
- This mechanism explains the rapid loss of mRNA observed following colchicine treatment.