Identification Of MAPK Pathways And VPS Genes Involved In Cadmium Tolerance In Saccharomyces Cerevisiae

Cadmium is a ubiquitous environmental pollutant and human carcinogen. In cells, cadmium exerts multiple toxic effects and affects cell proliferation, differentiation, apoptosis and other cellular activities. From a genome-scale genetic screen, we have identified 94 cadmium-sensitive gene mutations in Saccharomyces cerevisiae. Twenty-nine of these identified cadmium-sensitive mutations are of genes previously reported to be involved in the vacuolar protein sorting (VPS) pathway. Accordingly, the cadmium-sensitive phenotypes for seventeen identified VPS mutants correlate to their intracellular cadmium contents in response to oxidative stress. Genes for these VPS mutants mainly function in GTPase/ATPase, ESCRT complex and HOPS complexes. This suggests that these macromolecules are essential for maintaining intracellular ion homeostasis in yeast cells. The rest of other sixty-five genes for cadmium-sensitive mutations are involved in various functions including transcription and cell stress, signal transduction, and cell cycle. Interestingly, key components of two MAPK pathways, the HOG MAPK pathway and the CWI MAPK pathway, are hypothetically involved in cadmium tolerance. To further study the relationship between MAPK pathway and cadmium tolerance, we constructed three reporter genes STL1p-lacZ, CWP1p-lacZ and MPK1p-lacZ, which are regulated by HOG pathway and CWI pathway. We assayed the activity ofβ- galactosidase expressed by reporters and found that expression of CWP1p-lacZ and MPK1p-lacZ were induced in response to the stimulation of cadmium, which indicates that expression of CWP1 and MPK1 responds to cadmium stress.