The pivotal role of KCC2 and NKCC1 in development and maintenance of fast inhibitory
neurotransmission and their implication in severe human diseases arouse interest in posttranscriptional regulatory mechanisms such as (de)phosphorylation. Staurosporine (broad
kinase inhibitor) and N-ethylmalemide (NEM) that modulate kinase and ...
The pivotal role of KCC2 and NKCC1 in development and maintenance of fast inhibitory
neurotransmission and their implication in severe human diseases arouse interest in posttranscriptional regulatory mechanisms such as (de)phosphorylation. Staurosporine (broad
kinase inhibitor) and N-ethylmalemide (NEM) that modulate kinase and phosphatase activities enhance KCC2 and decrease NKCC1 activity. Here, we investigated the regulatory
mechanism for this reciprocal regulation by mass spectrometry and immunoblot analyses
using phospho-specific antibodies. Our analyses revealed that application of staurosporine
or NEM dephosphorylates Thr1007 of KCC2, and Thr203, Thr207 and Thr212 of NKCC1.
Dephosphorylation of Thr1007 of KCC2, and Thr207 and Thr212 of NKCC1 were previously
demonstrated to activate KCC2 and to inactivate NKCC1. In addition, application of the two
agents resulted in dephosphorylation of the T-loop and S-loop phosphorylation sites Thr233
and Ser373 of SPAK, a critical kinase in the WNK-SPAK/OSR1 signaling module mediating
phosphorylation of KCC2 and NKCC1. Taken together, these results suggest that reciprocal
regulation of KCC2 and NKCC1 via staurosporine and NEM is based on WNK-SPAK/OSR1
signaling. The key regulatory phospho-site Ser940 of KCC2 is not critically involved in the
enhanced activation of KCC2 upon staurosporine and NEM treatment, as both agents have
opposite effects on its phosphorylation status. Finally, NEM acts in a tissue-specific manner
on Ser940, as shown by comparative analysis in HEK293 cells and immature cultured hippocampal neurons. In summary, our analyses identified phospho-sites that are responsive to
staurosporine or NEM application. This provides important information towards a better
understanding of the cooperative interactions of different phospho-sites