Tr. Johnson et al., Regulation of dual-specificity phosphatases M3/6 and hVH5 by phorbol esters - Analysis of a delta-like domain, J BIOL CHEM, 275(41), 2000, pp. 31755-31762
Treatment of leukemic cells with phorbol 12-myristate 13-acetate (PMA) indu
ces a short-lived phosphorylation and activation of stress-activated protei
n kinase (SAPK) and cellular differentiation. To investigate whether the ra
pid deactivation of SAPK results from dephosphorylation by dual-specificity
phosphatases (DSPs), we studied regulation of the DSP hVH5 and its murine
orthologue M3/6 in K562 human leukemia cells. PMA treatment rapidly induced
hVH5 transcripts in these cells, and induced expression of M3/6 completely
inhibited PMA-stimulated phosphorylation of SAPK, suggesting a feedback lo
op to control SAPK activity. Using both stable cell lines and transient tra
nsfection we demonstrate that activation of SAPK rapidly stimulated phospho
rylation of M3/6. This phosphorylation did not regulate the half-life of to
tal cellular M3/6. hVH5 and M3/6 shares with all sequenced mammalian DSPs a
n amino acid motif, XILPXLXL, located approximately 80 amino acids from the
active site. The hVH5-M3/6 sequence, RILPHLYL, shares significant homology
with the SAPK binding site of the c-Jun protein, called the delta domain.
This motif was found to be important for DSP function, because deletion of
RILPHLYL inhibits SAPK-mediated phosphorylation of M3/6, and deletion of th
is sequence or mutation of the Ln portion blocks the ability of this phosph
atase to dephosphorylate SAPK.