Tissue-specific expression and endogenous subcellular distribution of the inositol 1,3,4,5-tetrakisphosphate-binding proteins GAP1(IP4BP) and GAP1(m).
GAP1(IP4BP) and GAP1(m) belong to the GAP1 family of Ras GTPase-activating proteins that are candidate InsP4 receptors. Here we show they are ubiquitously expressed in human tissues and are likely to have tissue-specific splice variants. Analysis by subcellular fractionation of RBL-2H3 rat basophilic leukemia cells confirms that endogenous GAP1(IP4BP) is primarily localised to the plasma membrane, whereas GAP1(m) appears localised to the cytoplasm (cytosol and internal membranes) but not the plasma membrane. Subcellular fractionation did not indicate a specific co-localisation between membrane-bound GAP1(m) and several Ca2+ store markers, consistent with the lack of co-localisation between GAP1(m) and SERCA1 upon co-expression in COS-7 cells. This difference suggests that GAP1(m) does not reside at a site where it could regulate the ability of InsP4 to release intracellular Ca2+. As GAP1(m) is primarily localised to the cytosol of unstimulated cells it may be spatially regulated in order to interact with Ras at the plasma membrane.
Department of Biochemistry, School of Medical Sciences, University of Bristol, United Kingdom.
P J
PJ
Lockyer
S
S
Vanlingen
J S
JS
Reynolds
T J
TJ
McNulty
R F
RF
Irvine
J B
JB
Parys
P J
PJ
Cullen
D000818:Animals; D019556:COS Cells; D000252:Calcium-Transporting ATPases / Q000096:biosynthesis; D002352:Carrier Proteins / Q000096:biosynthesis / Q000378:metabolism*; D019084:Fluorescent Antibody Technique, Indirect; D020558:GTP Phosphohydrolases / Q000378:metabolism; D006367:HeLa Cells; D006801:Humans; D007295:Inositol Phosphates / Q000378:metabolism*; D015471:Leukemia, Basophilic, Acute; D009928:Organ Specificity; D014176:Protein Biosynthesis; D011506:Proteins / Q000378:metabolism*; D051381:Rats; D018160:Receptors, Cytoplasmic and Nuclear / Q000378:metabolism*; D013347:Subcellular Fractions / Q000378:metabolism; D014407:Tumor Cells, Cultured; D020703:ras GTPase-Activating Proteins
D002352:Carrier Proteins; D007295:Inositol Phosphates; D011506:Proteins; C102193:RASA2 protein, human; D018160:Receptors, Cytoplasmic and Nuclear; C061107:inositol-1,3,4,5-tetrakisphosphate receptor; D020703:ras GTPase-Activating Proteins; C081655:inositol-1,3,4,5-tetrakisphosphate; D020558:GTP Phosphohydrolases; D000252:Calcium-Transporting ATPases