cAMP-dependent protein kinase phosphorylates and activates nuclear Ca2+-ATPase.
A Ca2+-pump ATPase, similar to that in the endoplasmic reticulum, has been located on the outer membrane of rat liver nuclei. The effect of cAMP-dependent protein kinase (PKA) on nuclear Ca2+-ATPase (NCA) was studied by using purified rat liver nuclei. Treatment of isolated nuclei with the catalytic unit of PKA resulted in the phosphorylation of a 105-kDa band that was recognized by antibodies specific for sarcoplasmic reticulum Ca2+-ATPase type 2b. Partial purification and immunoblotting confirmed that the 105-kDa protein band phosphorylated by PKA is NCA. The stoichiometry of phosphorylation was 0.76 mol of phosphate incorporated/mol of partially purified enzyme. Measurement of ATP-dependent 45Ca2+ uptake into purified nuclei showed that PKA phosphorylation enhanced the Ca2+-pumping activity of NCA. We show that PKA phosphorylation of Ca2+-ATPase enhances the transport of 10-kDa fluorescent-labeled dextrans across the nuclear envelope. The findings reported in this paper are consistent with the notion that the crosstalk between the cAMP/PKA- and Ca2+-dependent signaling pathways identified at the cytoplasmic level extends to the nucleus. Furthermore, these data support a function for crosstalk in the regulation of calcium-dependent transport across the nuclear envelope.
Laboratoire de Neurobiologie Moléculaire des Interactions Cellulaires, UPR 416 du Centre National de la Recherche Scientifique, 5 rue Blaise Pascal, 67084 Strasbourg, France.
P J
PJ
Rogue
J P
JP
Humbert
A
A
Meyer
S
S
Freyermuth
M M
MM
Krady
A N
AN
Malviya
D000818:Animals; D001692:Biological Transport; D015153:Blotting, Western; D000252:Calcium-Transporting ATPases / Q000302:isolation & purification / Q000378:metabolism*; D002467:Cell Nucleus / Q000201:enzymology*; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism*; D004789:Enzyme Activation; D010766:Phosphorylation; D051381:Rats
D017868:Cyclic AMP-Dependent Protein Kinases; D000252:Calcium-Transporting ATPases