Compensatory Internalization of Pma1 in V-ATPase Mutants in Saccharomyces cerevisiae Requires Calcium- and Glucose-Sensitive Phosphatases

摘要

Loss of V-ATPase activity in organelles, whether through V-ATPase inhibition or V-ATPase (vma) mutations, triggers a compensatory downregulation of the essential plasma membrane proton pump in Saccharomyces cerevisiae. We have previously determined that the α-arrestin and ubiquitin ligase are essential for ubiquination and endocytosis in response to loss of V-ATPase activity. Here, we show that endocytosis in V-ATPase mutants does not require pathway components upstream and downstream of , indicating that is acting independently in internalization. We find that two phosphatases, the calcium-responsive phosphatase calcineurin and the glucose-sensitive phosphatase (), and one of the regulatory subunits , exhibit negative synthetic genetic interactions with vma mutants, and demonstrate that both phosphatases are essential for ubiquitination and endocytic downregulation of in these mutants. Although both acute and chronic loss of V-ATPase activity trigger the internalization of ∼50% of surface , a comparable reduction in expression in a href="http://www.yeastgenome.org/locus/S000002976/overview" data-ga-action="click_feat_suppl" ref="reftype=extlink&article-id=5788529&issue-id=305641&journal-id=301&FROM=Article%7CFront%20Matter&TO=External%7CLink%7CURI" target="_blank">pma1-007 mutant neither compensates for loss of V-ATPase activity nor stops further href="http://www.yeastgenome.org/locus/S000002976/overview" data-ga-action="click_feat_suppl" ref="reftype=extlink&article-id=5788529&issue-id=305641&journal-id=301&FROM=Article%7CFront%20Matter&TO=External%7CLink%7CURI" target="_blank">Pma1 endocytosis. The results indicate that the cell surface level of href="http://www.yeastgenome.org/locus/S000002976/overview" data-ga-action="click_feat_suppl" ref="reftype=extlink&article-id=5788529&issue-id=305641&journal-id=301&FROM=Article%7CFront%20Matter&TO=External%7CLink%7CURI" target="_blank">Pma1 is not directly sensed and that internalized href="http://www.yeastgenome.org/locus/S000002976/overview" data-ga-action="click_feat_suppl" ref="reftype=extlink&article-id=5788529&issue-id=305641&journal-id=301&FROM=Article%7CFront%20Matter&TO=External%7CLink%7CURI" target="_blank">Pma1 may play a role in compensating for loss of V-ATPase-dependent acidification. Taken together, these results provide new insights into cross talk between two major proton pumps central to cellular pH control.