Inhibition of protein phosphatase 1 stimulates secretion of Alzheimer amyloid precursor protein.
BACKGROUND
Aberrant metabolism of the Alzheimer amyloid precursor protein (APP) or its amyloidogenic A beta fragment is thought to be centrally involved in Alzheimer's disease. Nonamyloidogenic processing of APP involves its cleavage within the A beta domain by a protease, termed alpha-secretase, and release of the large extracellular domain, termed APPS. Secretion of APPS can be stimulated by phorbol esters, activators of protein kinase C, with concurrent inhibition of A beta production. While the role of protein kinases of APP metabolism has been investigated, considerably less effort has been devoted to elucidating the role played by protein phosphatases. Okadaic acid, a protein phosphatase inhibitor, has been shown to stimulate secretion of APPS, but the identity of the phosphatase involved has not been investigated.


METHODS
The secretion of APPS from COS-1 cells was measured in the absence or presence of various doses of serine/threonine-specific phosphatase inhibitors. Quantitation of the derived IC50 values was used to determine the identity of the phosphatase involved in the control of APP secretion.


RESULTS
The availability of protein phosphatase inhibitors with different relative potencies against the different types of serine/threonine-specific protein phosphatase allowed us to examine which of the four known types of protein phosphatase might be involved in the regulation of APP secretion. Both okadaic acid and calyculin A stimulated the secretion of APP from COS-1 cells in a dose-dependent manner. The half-maximal dose for stimulation of APP secretion was approximately 100-fold higher with okadaic acid than with calyculin A.


CONCLUSIONS
The nearly 100-fold difference in the observed IC50 values for okadaic acid and calyculin A implicates a type 1 protein phosphatase in the control of APPS production. Protein phosphatase 1 (PP1) is known to be highly expressed in adult mammalian brain, both in neurons and glia. The identification of a specific phosphatase type in the control of APP secretion opens new avenues to the development of rational therapeutic intervention strategies aimed at the prevention and/or treatment of Alzheimer's Disease.
Rockefeller University, Laboratory of Molecular and Cellular Neuroscience, New York, New York 10021, USA.
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da Cruz e Silva
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da Cruz e Silva
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Zaia
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Greengard
D000368:Aged; D000544:Alzheimer Disease / Q000378:metabolism*; D000682:Amyloid / Q000378:metabolism*; D053829:Amyloid Precursor Protein Secretases; D016282:Aspartic Acid Endopeptidases; D002193:Cantharidin / Q000494:pharmacology; D002460:Cell Line; D010450:Endopeptidases / Q000378:metabolism; D004791:Enzyme Inhibitors / Q000494:pharmacology; D004988:Ethers, Cyclic / Q000494:pharmacology; D006801:Humans; D015151:Immunoblotting; D008387:Marine Toxins; D019319:Okadaic Acid; D010080:Oxazoles / Q000494:pharmacology; D015240:Phorbol 12,13-Dibutyrate / Q000494:pharmacology; D010749:Phosphoprotein Phosphatases / Q000037:antagonists & inhibitors*; D000072002:Prion Proteins; D011328:Prions; D054645:Protein Phosphatase 1; D011498:Protein Precursors / Q000378:metabolism*
D000682:Amyloid; D004791:Enzyme Inhibitors; D004988:Ethers, Cyclic; D008387:Marine Toxins; D010080:Oxazoles; C512656:PRNP protein, human; D000072002:Prion Proteins; D011328:Prions; D011498:Protein Precursors; D019319:Okadaic Acid; D015240:Phorbol 12,13-Dibutyrate; C059041:calyculin A; D010749:Phosphoprotein Phosphatases; D054645:Protein Phosphatase 1; D053829:Amyloid Precursor Protein Secretases; D010450:Endopeptidases; D016282:Aspartic Acid Endopeptidases; C509280:BACE1 protein, human; D002193:Cantharidin