REGULATION OF ERK2 DEPHOSPHORYLATION IN G(1)-STIMULATED RAT T-LYMPHOBLASTS

Rat T lymphoblasts arrested in the G(1) phase of the cell cycle by int erleukin-2 (IL-2) deprivation can be forced to proceed to the S phase when they are stimulated with IL-2 or the phorbol ester phorbol 12,13- dibutyrate (PDBu). When PDBu is used as a stimulus, extracellular regu lated kinase 2 (ERK2) is activated by threonine and tyrosine phosphory lation by the dual-specificity kinase MEK. Here we have studied the re gulation of ERK2 dephosphorylation as a mechanism for inactivation of this kinase. In vivo inhibition of ERK2 dephosphorylation observed aft er preincubation with translation or transcription inhibitors (cyclohe ximide or actinomycin. respectively) indicates the involvement of at l east one inducible phosphatase, the best candidate for which is the du al-specificity phosphatase PAC-1. Other noninducible phosphatases must act as well, however, because sodium orthovanadate is a more effectiv e dephosphorylation blocker than cycloheximide. In addition, the okada ic acid effect in ERK2 dephosphorylation indicates that Ser/Thr phosph atases are also involved, directly and/or indirectly.