Activation of peripheral large granular lymphocytes with the serine/threonine phosphatase inhibitor, okadaic acid

摘要

AbstractThe murine polyether fatty acid, okadaic acid, is a potent inhibitor of serine/threonine phosphatases in eukaryotic cells. This compound inhibits both protein phosphatase 1 (PP1) and phosphatase 2A (PP2A). Here we have examined the potential of okadaic acid as an activator of fresh peripheral CD3‐large granular lymphocytes (LGL). We demonstrate that overnight exposure of LGL to as little as 1 nM okadaic acid induced an increase in natural killing against the K562 cell line, but does not induce LAK activity. Optimal cytotoxic activation (2‐fold) occurred at 0.01‐‐1.0 nM okadaic acid, with a return to baseline levels at 10‐‐20 nM, and inhibition, likely due to toxicity, at 40 nM. In addition, okadaic acid at doses ⩾20 nM induced LGL but not T cells to produce interferon‐γ. Similar to phorbol esters, overnight incubation with okadaic acid causes a dose‐dependent reduction in expression of the low‐affinity receptor for the Fc portion of IgG (CD16). However, unlike phorbol ester, short‐term (5 min) okadaic acid treatment did not block CD16‐mediated Ca2+mobilization in LGL. To address the underlying biochemical mechanisms of okadaic acid activities, the levels of several as‐yet‐unidentified serine/threonine kinases were assayed after renaturation. Under these conditions, okadaic acid induced similar increases in kinase levels in both T cells and LGL. Taken together, these data suggest an important role for PP1 and PP2A in LGL physiology, and define okadaic acid as a potentially important biological response modifier for the study of LGL and Tcell biochemistry, signal transduction, an