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Protein kinase A is required for resistance to the lysosomotropic drugs quinacrine and chloroquine in the fission yeast, Schizosaccharomyces pombe

Yeast vacuoles, the functionally diverse counterparts of mammalian lysosomes, are highly dynamic organelles that undergo morphological changes during the cell cycle and in response to various cellular stresses. Here, we report results of an investigation on the contribution of protein kinase A (PKA) to vacuole integrity and dynamics in the fission yeast, Schizosaccharomyces pombe. Under normal culturing conditions, vacuoles in S. pombe wild type cells and PKA null (pka1Δ) mutants appear similar in size, morphology, and distribution. Wild type and pka1Δ cells also exhibit similar intensities of staining with quinacrine, a fluorescent lysosomotropic drug that accumulates in acidic organelles, indicating that PKA is not required for vacuole acidification in S. pombe. However, whereas quinacrine induces coalescence of vacuoles in wild type S. pombe cells, it does not induce a similar response in pka1Δ cells. Moreover, pka1Δ mutants are hypersensitive to the growth inhibitory effects of both quinacrine and the lysosomotropic toxin, chloroquine. Interestingly, we also found that the toxin rotenone, while having no obvious affect on vacuole morphology in wild type S. pombe cells, induced formation of small vacuoles aggregated at the nuclear periphery in pka1Δ cells, which are hypersensitive to growth inhibitory effects of the toxin. Our findings implicate PKA as a mediator of vacuole stress response in S. pombe.