A Chinese hamster ovary cell mutant with a heat-sensitive, conditional-lethal defect in vacuolar function

Area of Science:

• Cell Biology
• Genetics
• Biochemistry

Background:

• Chinese hamster ovary (CHO) cells are widely used in cell biology research.
• Protein toxins often rely on cellular mechanisms like endocytosis and pH changes for entry.
• Temperature sensitivity in cell mutants can reveal critical cellular processes.

Purpose of the Study:

• To characterize a novel temperature-sensitive mutant (G.7.1) derived from CHO cells.
• To investigate the underlying molecular defect causing heat sensitivity and toxin resistance.
• To understand the role of vacuolar acidification in cellular viability and toxin sensitivity.

Main Methods:

• Cell culture at different temperatures (34°C and 39.5°C).
• Growth assays in supplemented and unsupplemented media.
• Toxin resistance assays (diphtheria toxin, modeccin, Pseudomonas aeruginosa exotoxin A).
• Assay of vacuolar acidification using acridine orange and cell-free vesicle preparations.

Main Results:

• Mutant G.7.1 exhibits normal growth at 34°C but fails to grow at 39.5°C in standard medium.
• Supplementation with FeSO4 rescues growth at the elevated temperature.
• G.7.1 cells demonstrate resistance to multiple protein toxins at 39.5°C.
• Vacuolar acidification in G.7.1 cells is heat-labile, indicating a defect in this process.

Conclusions:

• Mutant G.7.1 possesses a heat-sensitive defect impairing vacuolar acidification.
• This defect leads to temperature-sensitive growth and resistance to protein toxins.
• Impaired acidification hinders iron extraction from transferrin, impacting cell viability at higher temperatures.