Stress-activated protein kinase-3 (
SAPK3), a recently described MAP
kinase family member with a wide-spread tissue distribution, was transfected into several mammalian cell lines and shown to be activated in response to cellular stresses,
interleukin-1 (IL-1) and tumour
necrosis factor (TNF) in a similar manner to SAPK1 (also termed JNK) and
SAPK2 (also termed p38, RK, CSBP and Mxi2).
SAPK3 and
SAPK2 were activated at similar rates in vitro by SAPKK3 (also termed MKK6), and SAPKK3 was the only activator of
SAPK3 that was induced when KB or 293 cells were exposed to cellular stresses or stimulated with
IL-1 or TNF. Co-transfection with SAPKK3 induced
SAPK3 activity and greatly enhanced activation in response to osmotic shock. These experiments indicate that SAPKK3 mediates the activation of
SAPK3 in several mammalian cells.
SAPK3 and
SAPK2 phosphorylated a number of
proteins at similar rates, including the
transcription factors ATF2, Elk-1 and SAP1, but
SAPK3 was far less effective than
SAPK2 in activating
MAPKAP kinase-2 and
MAPKAP kinase-3. Unlike
SAPK2,
SAPK3 was not inhibited by the
drug SB 203580.
SAPK3 phosphorylated ATF2 at Thr69, Thr71 and Ser90, the same residues phosphorylated by SAPK1, whereas
SAPK2 only phosphorylated Thr69 and Thr71. Our results suggest that cellular functions previously attributed to SAPK1 and/or
SAPK2 may be mediated by
SAPK3.