5‐HT induces threonine (T375) phosphorylation of ADAM17/TACE cytoplasmic tail

Abstract

We have shown recently that TACE transactivates epidermal growth factor receptor (EGFR), and induces ERK phosphorylation (ERK‐P) and cellular proliferation upon 5‐HT2A receptor stimulation in renal mesangial cells.In this study our aim was to identify kinases responsible for TACE phosphorylation and potential activation during inter‐receptor cross‐talk. We detected robust threonine phosphorylation of TACE as early as 6 minutes following 5‐HT stimulation using a phospho‐threonine/proline antibody. This suggested phosphorylation of threonine 375, as this is the only threonine next to a proline present in the cytoplasmic tail of TACE. Using chemical inhibitors (naltrindole and PDK1/Akt/Flt dual pathway inhibitor) we showed that ERK phosphorylation is PDK1 dependent. Additionally, a MAPK cascade seems to have a role in TACE phosphorylation in that a MEK inhibitor (10 μM of PD989059) significantly attenuated 1 μM 5‐HT‐induced TACE phosphorylation. To study kinase‐induced activation of the enzyme we used a quenched fluorogenic TACE substrate. We found attenuation of 5‐HT‐induced TACE activity in PD989059‐pretreated cells. No serine phosphorylation of TACE upon 5‐HT stimulation was detected. Our data suggest that (1) either MEK itself or members of the MAPK family can be (directly or indirectly) responsible for TACE phosphorylation and activation during inter‐receptor crosstalk, and (2) multiple kinases contribute to TACE phosphorylation.This work was supported by NIH DK070054‐03 to M.G., T32 DK07752‐08 to C.L.R., NIH NCCR P20 RR016434 to P.G., NIH R01 DK55524 to L.M.L. and REAP from the VA Research Service.