Phosphoinositide metabolism and the calcium response to concanavalin A in S49 T-lymphoma cells. A comparison with thymocytes.
Comparisons were made between transformed S49 T-lymphoma cells and normal murine thymocytes in their polyphosphoinositides, inositol polyphosphates and cytosolic free calcium concentrations ([Ca2+]i), and the effects of the T-cell mitogen concanavalin A (Con A) on these properties. 1. The ratios of the polyphosphoinositides to phosphatidylinositol in both exponential-phase S49 cells and mitogen-stimulated thymocytes (G1 phase) were greater than in quiescent (G0-phase) thymocytes. 2. In response to Con A, the amount of phosphatidylinositol 4,5-bisphosphate (PtdInsP2) in S49 cells decreased slightly (17% in 30 min), and this was sufficient to account for the small amounts of inositol phosphates that accumulated. In contrast, it has been shown previously that Con A stimulates a rapid resynthesis of PtdInsP2 in thymocytes and the amounts of inositol phosphates released rapidly exceed the steady-state amount of the PtdInsP2 precursor [Taylor, Metcalfe, Hesketh, Smith & Moore (1984) Nature (London) 312, 462-465]. 3. The [Ca2+]i did not differ significantly in S49 cells and thymocytes before the addition of Con A, and the increases in [Ca2+]i in response to Con A were similar in both types of cell. 4. The [Ca2+]i increase in response to Con A was inhibited by similar concentrations of intracellular cyclic AMP (2-10 microM) in S49 cells and thymocytes, suggesting that similar regulatory mechanisms act on this response in both types of cell. The data demonstrate that the basal [Ca2+]i and phosphoinositide metabolism is similar in both the normal cells and their transformed counterparts. In addition, they suggest that the activated Con A receptors generate very similar signals in the two cell types, and that any perturbations of primary signal transduction to the secondary phosphoinositide and [Ca2+]i responses in the S49 phenotype are quantitative rather than qualitative.
Taylor
M V
MV
Department of Biochemistry, Cambridge, U.K.
Hesketh
T R
TR
Metcalfe
J C
JC
D000255:Adenosine Triphosphate / Q000378:metabolism; D000634:Aminoquinolines / Q000494:pharmacology; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002460:Cell Line; D003208:Concanavalin A / Q000494:pharmacology*; D000242:Cyclic AMP / Q000494:pharmacology; D005456:Fluorescent Dyes / Q000494:pharmacology; D007295:Inositol Phosphates / Q000378:metabolism; D008223:Lymphoma / Q000378:metabolism*; D051379:Mice; D008807:Mice, Inbred BALB C; D010716:Phosphatidylinositols / Q000378:metabolism*; D013601:T-Lymphocytes / Q000187:drug effects / Q000378:metabolism*
D000634:Aminoquinolines; D005456:Fluorescent Dyes; D007295:Inositol Phosphates; D010716:Phosphatidylinositols; D003208:Concanavalin A; D000255:Adenosine Triphosphate; D000242:Cyclic AMP; C035739:Quin2; D002118:Calcium