The Golgi-Ca2+-ATPase KlPmr1p function is required for oxidative stress response by controlling the expression of the heat shock element HSP60 in Kluyveromyces lactis.

The Golgi P-type Ca2+-ATPase, Pmr1p, is the major player for calcium homeostasis in yeast. The inactivation of KIPMR1 in Kluyveromyces lactis leads to high pleiotropic phenotypes that include reduced glycosylation, cell wall defects, and alterations of mitochondrial metabolism. In this article we found that cells lacking KlPmr1p have a morphologically altered mitochondrial network and that mitochondria (m) from Klpmr1 Delta cells accumulate Call more slowly and reach a lower [Ca2+](m) level, when exposed to [Ca2+] < 5 mu M, than wild-type cells. The Klpmr1 Delta cells also exhibit traits of ongoing oxidative stress and present hyperphosphorylation of KlHog1p, the hallmark for the activation of stress response pathways. The mitochondrial chaperone KIHsp60 acts as a multicopy suppressor of phenotypes that occur in cells lacking the Ca2+-ATPase, including relief from oxidative stress and recovery of cell wall thickness and functionality. Inhibition of KIPMR1 function decreases KlHSP60 expression at both mRNA and protein levels. Moreover, KIPRM1 loss of function correlates with both decreases in HSF DNA binding activity and KIHSP60 expression. We suggest a role for KIPMR1 in HSF DNA binding activity, which is required for proper KIHSP60 expression, a key step in oxidative stress response.