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Calcium is involved in EGF‐induced activation of ERK5 by mediating Lad‐MEKK2 interaction.
Author(s) -
Seger Rony,
Yoon Seunghee,
Kalie Eyal
Publication year - 2006
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.20.5.a983
Subject(s) - calcium , chemistry , microbiology and biotechnology , cytosol , stimulation , biophysics , endocrinology , biochemistry , biology , enzyme , organic chemistry
The ERK5 cascade is a MAPK pathway that transmits both mitogenic and stress signals, yet its mechanism of regulation is poorly understood. Here we undertook to elucidate the mechanism of activation of the ERK5 cascade in response to EGF stimulation. Using calcium chelators, we found that ERK5 activation by EGF is inhibited by the depletion of intracellular calcium levels. This calcium effect was found to occur at the MEKK2 level, upstream of the ERK5 cascade. Co‐immunoprecipitation studies revealed that EGF increases the binding of MEKK2 to the adaptor protein Lad, which is known to mediate EGF signals to ERK5. This Lad‐MEKK2 interaction was abolished by the calcium chelators, indicating that elevated calcium concentrations are required for the interactions, and thereby for the transmission of EGF signals to the ERK5 cascade. In addition, we found that while endogenous ERK5 and MEK5 are localized in the nucleus of resting and stimulated cells, MEKK2 is distributed all over resting cells, and upon EGF stimulation accumulates in the nucleus. The diffused cellular distribution of MEKK2 is probably caused by a free shuttle between the cytosol and the nucleus, as treatment with Leptomycin B resulted in a nuclear accumulation of the protein. Reduction in calcium levels inhibited the EGF‐induced MEKK2 translocation in a Lad‐independent manner, indicating that the effect of calcium on the translocation is probably due to the lack of MEKK2 activation. Taken together, these findings suggest that calcium is required for ERK5 activation by EGF by securing the proper interaction of the MEKK2 at the MAP3K level of this cascade with the upstream adaptor protein Lad.