Pacific origin of the abrupt increase in Indian Ocean heat content during the warming hiatus

Global mean surface warming has stalled since the end of the twentieth century1, 2, but the net radiation imbalance at the top of the atmosphere continues to suggest an increasingly warming planet. This apparent contradiction has been reconciled by an anomalous heat flux into the ocean3, 4, 5, 6, 7, 8, induced by a shift towards a La Niña-like state with cold sea surface temperatures in the eastern tropical Pacific over the past decade or so. A significant portion of the heat missing from the atmosphere is therefore expected to be stored in the Pacific Ocean. However, in situ hydrographic records indicate that Pacific Ocean heat content has been decreasing9. Here, we analyse observations along with simulations from a global ocean–sea ice model to track the pathway of heat. We find that the enhanced heat uptake by the Pacific Ocean has been compensated by an increased heat transport from the Pacific Ocean to the Indian Ocean, carried by the Indonesian throughflow. As a result, Indian Ocean heat content has increased abruptly, which accounts for more than 70% of the global ocean heat gain in the upper 700 m during the past decade. We conclude that the Indian Ocean has become increasingly important in modulating global climate variability

Protein Phosphatase 2A Interacts with the Na+,K+-ATPase and Modulates Its Trafficking by Inhibition of Its Association with Arrestin

Background: The P-type ATPase family constitutes a collection of ion pumps that form phosphorylated intermediates during ion transport. One of the best known members of this family is the Na +,K +-ATPase. The catalytic subunit of the Na +,K +-ATPase includes several functional domains that determine its enzymatic and trafficking properties. Methodology/Principal Findings: Using the yeast two-hybrid system we found that protein phosphatase 2A (PP2A) catalytic C-subunit is a specific Na +,K +-ATPase interacting protein. PP-2A C-subunit interacted with the Na +,K +-ATPase, but not with the homologous sequences of the H +,K +-ATPase. We confirmed that the Na +,K +-ATPase interacts with a complex of A- and C-subunits in native rat kidney. Arrestins and G-protein coupled receptor kinases (GRKs) are important regulators of G-protein coupled receptor (GPCR) signaling, and they also regulate Na +,K +-ATPase trafficking through direct association. PP2A inhibits association between the Na +,K +-ATPase and arrestin, and diminishes the effect of arrestin on Na +,K +-ATPase trafficking. GRK phosphorylates the Na +,K +-ATPase and PP2A can at least partially reverse this phosphorylation. Conclusions/Significance: Taken together, these data demonstrate that the sodium pump belongs to a growing list of io

Immunolocalization of the Na⁺,K⁺-ATPase and arrestin in the presence of PP2A in COS cells.

<p>COS cells were transfected with H85N plus Na⁺,K⁺-ATPase β-subunit (A), with H85N, Na⁺,K⁺-ATPase β-subunit and flag tagged arrestin (B-D), with H85N, Na⁺,K⁺-ATPase β-subunit and HA tagged PP2A C-subunit (E-G), or with H85N plus Na⁺,K⁺-ATPase β-subunit and flag tagged arrestin plus HA tagged PP2A C-subunit (H-M). Cells were stained with HK9 (A, B, E, H and K), anti-flag for arrestin (C and I), and anti-HA for PP2A C-subunit (F and L) antibodies. Overlay patterns are shown in D, G, J and M. (×200 magnification) A large fraction of the H85N was found in intracellular compartments when cells expressed arrestin in the absence of PP2A C-subunit. This effect was not observed when arrestin was expressed together with the PP2A C-subunit. Typical results from one of three experiments are shown.</p

Deletion constructs of the large cytoplasmic loop of the Na⁺,K⁺-ATPase α-subunit and GST pull down of PP2A with GST constructs.

<p>A. HA tagged PP2A C-subunit was expressed in COS cells and cell lysates were incubated with GST fusion proteins. PP2A C-subunit was detected by Western blot with anti-HA antibody (upper panel) and GST fusion proteins were detected by CBB staining. Not only N-terminal segments but also the C-terminal half of the large cytoplasmic loop binds to PP2A C-subunit. Typical results from one of four experiments are shown. B. Flag tagged PP2A A-subunit was expressed in COS cells and cell lysates were incubated with GST fusion proteins. PP2A A-subunit was detected by Western blot with anti-flag antibody (upper panel) and GST fusion proteins were detected by CBB staining. The PP2A A-subunit co-precipitated with the A-domain of the Na⁺,K⁺-ATPase α-subunit. Typical results from one of three experiments are shown.</p

In vitro translation of PP2A and pull down with a GST construct incorporating the large cytoplasmic loop of the Na⁺,K⁺-ATPase α-subunit.

<p>PP2A A (flag tagged)- and C (HA tagged)- subunit proteins were prepared by in vitro translation and GST pull down was performed with GST alone or GST-Na⁺,K⁺-ATPase large cytoplasmic loop (Na,K-GST). A. GST proteins used for pull down were detected by coomassie brilliant blue (CBB) staining. PP2A C-subunit and A-subunit were detected by Western blot with anti-HA (B) and anti-flag (C) antibodies, respectively. The PP2A C-subunit, but not the A-subunit, specifically co-precipitate with the GST-Na⁺,K⁺-ATPase. Typical results from one of three experiments are shown.</p

Competition between PP2A and arrestin for binding to the large cytoplasmic loop of the Na⁺,K⁺-ATPase.

<p>COS cell lysates expressing flag tagged arrestin 2 or HA tagged PP2A C-subunit were prepared. A. Coomassie Brilliant Blue staining demonstrating that the same quantities of GST fusion protein incorporating the large cytoplasmic loop of the Na⁺,K⁺-ATPase were used in each lane of the experiments depicted in panels B and C. B. GST fusion protein incorporating the large cytoplasmic loop of the Na⁺,K⁺-ATPase was incubated with 500 µl of lysate from arrestin2-expressing cells and varying amounts of lysate from PP2A C-subunit-expressing cells. Arrestin 2 (upper panel) and PP2A C-subunit (lower panel) were detected by western blotting using an anti-flag and anti-HA antibodies, respectively. C. GST fusion protein incorporating the large cytoplasmic loop of the Na⁺,K⁺-ATPase was incubated with 500 µl of lysate from PP2A C-subunit-expressing cells and varying amounts of lysate from arrestin 2-expressing cells. PP2A C-subunit (upper panel) and arrestin 2 (lower panel) were detected by western blotting with an anti-HA and anti-flag antibodies, respectively. Arrestin 2 binding to the Na⁺,K⁺-ATPase large loop was strongly inhibited by the PP2A C-subunit. Typical results from one of three experiments are shown.</p

Immunoprecipitation of Na⁺,K⁺-ATPase and PP2A from rat kidney.

<p>Rat kidney lysate was incubated with antibodies directed against the PP2A C-subunit, the PP2A A-subunit or the HA epitope (control) followed by protein A beads. As an additional control for the fact that the Na,K-ATPase α-subunit migrates in SDS-PAGE in close proximity to the band corresponding to IgG heavy chain dimers, the antibodies directed against the PP2A A-subunit or C-subunit were incubated with lysis buffer without the addition of tissue lysate. Immune complexes were separated by SDS-PAGE and Western blotting was performed with biotinylated anti Na⁺,K⁺-ATPase antibody, 6H. The Na⁺,K⁺-ATPase was co-precipitated with both the C- and A-subunits of PP2A. Typical results from one of three experiments are shown.</p