Expression, regulation and role of the MAGUK protein SAP-97 in human atrial myocardium.
OBJECTIVE
In various cell types, membrane-associated guanylate kinases proteins called MAGUK play a major role in the spatial localization and clustering of ion channels. Here, we studied the expression and role of these anchoring proteins in human right atrial myocardium by means of various molecular, biochemical and physiological methods.


RESULTS
SAP-97, PSD-95, Chapsyn and SAP-102 messengers were detected by reverse transcriptase-polymerase chain reaction (RT-PCR) on mRNA extracted from both whole myocardium and isolated myocytes. Western blot revealed that the MAGUK protein SAP-97 and, to a lesser extent, PSD-95, is abundantly expressed in human atrial myocardium, while Chapsyn are almost undetectable. Confocal microscopic visualization of cryosection of atrial myocardium stained with the anti-PSD-95 family antibody showed positive staining at the plasma membrane level and cell extremity. Calpain-I cleaved both SAP-97 and PSD-95 proteins, resulting in an accumulation of short bands, including an 80-kDa band that was also detected in the cytosolic protein fraction. Immunoprecipitation of SAP-97 co-precipitated hKv1.5 channels, and vice versa. Co-expression of cloned SAP-97 and hKv1.5 channels in Chinese hamster ovarian (CHO) cells increased the K(+) current (157.00+/-19.45 pA/pF vs. 344.50+/-58.58 pA/pF at +50 mV).


CONCLUSIONS
The protein SAP-97 is abundantly expressed in human atrial myocardium in association with hKv1.5 channels, and probably contributes to regulating the functional expression of the latter.
Godreau
David
D
INSERM Unité 460, Faculté de Médecine Xavier Bichat, 16 rue Henri Huchard, 75018, Paris, France.
Vranckx
Roger
R
Maguy
Ange
A
Rücker-Martin
Catherine
C
Goyenvalle
Catherine
C
Abdelshafy
Salah
S
Tessier
Sophie
S
Couétil
Jean Paul
JP
Hatem
Stéphane N
SN
D048868:Adaptor Proteins, Signal Transducing; D000818:Animals; D016466:CHO Cells; D002154:Calpain / Q000494:pharmacology; D006224:Cricetinae; D000074288:Discs Large Homolog 1 Protein; D005786:Gene Expression Regulation; D051528:Guanylate Kinases; D006325:Heart Atria / Q000378:metabolism; D006801:Humans; D051666:Kv1.5 Potassium Channel; D008565:Membrane Proteins; D009206:Myocardium / Q000378:metabolism*; D032383:Myocytes, Cardiac / Q000378:metabolism; D009419:Nerve Tissue Proteins / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D009703:Nucleoside-Phosphate Kinase / Q000378:metabolism; D018408:Patch-Clamp Techniques; D015221:Potassium Channels / Q000378:metabolism; D024642:Potassium Channels, Voltage-Gated; D012333:RNA, Messenger / Q000235:genetics; D051381:Rats; D020133:Reverse Transcriptase Polymerase Chain Reaction; D014162:Transfection; D025521:Tumor Suppressor Proteins
D048868:Adaptor Proteins, Signal Transducing; C513314:DLG1 protein, human; D000074288:Discs Large Homolog 1 Protein; C501119:Dlg1 protein, rat; C496981:KCNA5 protein, human; C496983:Kcna5 protein, rat; D051666:Kv1.5 Potassium Channel; D008565:Membrane Proteins; D009419:Nerve Tissue Proteins; D015221:Potassium Channels; D024642:Potassium Channels, Voltage-Gated; D012333:RNA, Messenger; D025521:Tumor Suppressor Proteins; D009703:Nucleoside-Phosphate Kinase; C496468:DLG2 protein, human; D051528:Guanylate Kinases; D002154:Calpain