INOSITOL-1,3,4,5-TETRAKISPHOSPHATE BINDING-SITES IN CONTROL AND RAS-TRANSFORMED NIH 3T3 FIBROBLASTS/

Inositol-1,3,4,5-tetrakisphosphate (Ins(1,3,4,5)P-4) binding propertie s were investigated in NIH/3T3 fibroblasts and its ras-transformant (D T cells), in which inositol tetrakisphosphates induce Ca2+ influx. [H- 3]Ins(1,3,4,5)P-4 bound to membranes of both types of cells with Kd va lues of 10.6 and 8.6 nM, respectively. The rank order of inositol poly phosphates for displacing [H-3]Ins(1,3,4,5)P-4 in DT cells was Ins(1,3 ,4,5)P-4 > inositol-1,3,4,5,6-pentakisphosphate > inositol hexakisphos phate > inositol-1,4,5-trisphosphate. This order is similar to that re ported in two Ras-GTPase-activating proteins, GAP1(IP4BP) and GAP1(m), which are also the Ins(1,3,4,5)P-4 binding proteins. Northern blot an alysis revealed that NIH/3T3 and DT cells expressed mRNA species that were hybridizable with GAP1(m) cDNA. These results suggest that parent al and ras-transformed NIH/3T3 fibroblasts possess GAP1-like proteins, which may be responsible for triggering inositol tetrakisphosphate-de pendent Ca-2 influx. (C) 1997 Academic Press.