P5A-Type ATPase Cta4p Is Essential for Ca2+ Transport in the Endoplasmic Reticulum of Schizosaccharomyces pombe

This study establishes the role of P5A-type Cta4 ATPase in Ca2+ sequestration in the endoplasmic reticulum by detecting an ATP-dependent, vanadate-sensitive and FCCP insensitive 45Ca2+-transport in fission yeast membranes isolated by cellular fractionation. Specifically, the Ca2+-ATPase transport activity was decreased in ER membranes isolated from cells lacking a cta4+ gene. Furthermore, a disruption of cta4+ resulted in 6-fold increase of intracellular Ca2+ levels, sensitivity towards accumulation of misfolded proteins in ER and ER stress, stimulation of the calcineurin phosphatase activity and vacuolar Ca2+ pumping. These data provide compelling biochemical evidence for a P5A-type Cta4 ATPase as an essential component of Ca2+ transport system and signaling network which regulate, in conjunction with calcineurin, the ER functionality in fission yeast

Spermine modulates fungal morphogenesis and activates plasma membrane H+-ATPase during yeast to hyphae transition

Polyamines play a regulatory role in eukaryotic cell growth and morphogenesis. Despite many molecular advances, the underlying mechanism of action remains unclear. Here, we investigate a mechanism by which spermine affects the morphogenesis of a dimorphic fungal model of emerging relevance in plant interactions, Yarrowia lipolytica, through the recruitment of a phytohormone-like pathway involving activation of the plasma membrane P-type H+-ATPase. Morphological transition was followed microscopically, and the H+-ATPase activity was analyzed in isolated membrane vesicles. Proton flux and acidification were directly probed at living cell surfaces by a non-invasive selective ion electrode technique. Spermine and indol-3-acetic acid (IAA) induced the yeast-hypha transition, influencing the colony architecture. Spermine induced H+-ATPase activity and H+ efflux in living cells correlating with yeast-hypha dynamics. Pharmacological inhibition of spermine and IAA pathways prevented the physio-morphological responses, and indicated that spermine could act upstream of the IAA pathway. This study provides the first compelling evidence on the fungal morphogenesis and colony development as modulated by a spermine-induced acid growth mechanism analogous to that previously postulated for the multicellular growth regulation of plants

Arbuscular mycorrhizal fungi induce differential activation of the plasma membrane and vacuolar H+ pumps in maize roots.

Roots undergo multiple changes as a consequence of arbuscular mycorrhizal (AM) interactions. One of the major alterations expected is the induction of membrane transport systems, including proton pumps. In this work, we investigated the changes in the activities of vacuolar and plasma membrane (PM) H(+) pumps from maize roots (Zea mays L.) in response to colonization by two species of AM fungi, Gigaspora margarita and Glomus clarum. Both the vacuolar and PM H(+)-ATPase activities were inhibited, while a concomitant strong stimulation of the vacuolar H(+)-PPase was found in the early stages of root colonization by G. clarum (30 days after inoculation), localized in the younger root regions. In contrast, roots colonized by G. margarita exhibited only stimulation of these enzymatic activities, suggesting a species-specific phenomenon. However, when the root surface H(+) effluxes were recorded using a noninvasive vibrating probe technique, a striking activation of the PM H(+)-ATPases was revealed specifically in the elongation zone of roots colonized with G. clarum. The data provide evidences for a coordinated regulation of the H(+) pumps, which depicts a mechanism underlying an activation of the root H(+)-PPase activity as an adaptative response to the energetic changes faced by the host root during the early stages of the AM interaction

Mutant <i>cta4Δ</i> displays higher calcineurin phosphatase activity.

<p>The calcineurin protein phosphatase activity was determined by the amount of free phosphate released. The reaction was started by adding the cellular extracts, followed by incubation at 30°C for 30 min with the RII phosphopeptide substrate. Values are means (± SE) of three independent experiments.</p

The growth of <i>cta4Δ</i> is impaired by endoplasmic reticulum stress.

<p>Wild-type and <i>cta4Δ</i> cells were serially diluted in five-fold steps, spotted onto YES plates containing 0.4% DTT and 0.05 µg/mL tunicamycin and incubated for 3 days at 30°C.</p

<i>cta4⁺</i> is required for Ca²⁺-ATPase activity in ER membrane fractions.

<p>Total membranes were isolated from wt and <i>cta4Δ</i> cells and fractionated on 12-step sucrose density gradient. (A) ATP-dependent FCCP-insensitive ⁴⁵Ca²⁺ uptake in the membrane fractions was measured after 10 min of incubation as described in Materials and <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0027843#s2" target="_blank">Methods</a>. Sucrose concentration of each fraction is shown. (B) Dotblot of selected gradient fractions (fraction numbers are indicated) was used for immunolocalization of Cta4-GFP using anti-GFP antibodies. (C) Inhibition of ATP-dependent FCCP-insensitive ⁴⁵Ca²⁺ transport in ER membrane fractions by vanadate (Na₃VO₄), the inhibitor of P-type ATPases. <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0027843#s3" target="_blank">Results</a> shown are representative of three independent experiments. Abbreviation used: NE, nuclear envelope; ER, endoplasmic reticulum; Vac, vacuole.</p

Calcineurin inhibition stimulated ⁴⁵Ca²⁺ accumulation in wt and <i>cta4Δ</i> mutant cells.

<p>The accumulation of ⁴⁵Ca²⁺ in wild-type and <i>cta4Δ</i> yeast cells was measured after 5 hours of addition of ⁴⁵Ca²⁺ to YES medium containing 10 µg/mL cyclosporin A (CsA). Values are means (± SE) of three independent experiments.</p

Endoplasmic reticulum stress caused by inhibition of glycosylation stimulates an increase of Ca²⁺ accumulation.

<p>The accumulation of ⁴⁵Ca²⁺ in wild-type and <i>cta4Δ</i> yeast cells was measured after 5 hours of addition of ⁴⁵Ca²⁺ to YES medium containing 0.125 µg/mL tunicamycin. Values are means (± SE) of three independent experiments.</p