A dual phosphorylation switch controls 14-3-3-dependent cell surface expression of TASK-1

Area of Science:

• Molecular biology
• Cellular transport mechanisms
• Ion channel regulation

Background:

• The cell surface transport of K(+) channels TASK-1 (KCNK3) and TASK-3 (KCNK9) is regulated by 14-3-3 proteins binding to their C-terminal trafficking control region.
• A current model suggests 14-3-3 binding, dependent on phosphorylation, sterically hinders a COPI-binding motif.

Purpose of the Study:

• To investigate the direct effects of phosphorylation on COPI binding.
• To quantify the binding parameters of all human 14-3-3 isoforms to TASK-1 and TASK-3 trafficking regions.
• To elucidate the dynamic regulation of TASK-1 and TASK-3 channel transport.

Main Methods:

• Quantitative analysis of 14-3-3 isoform binding to TASK-1 and TASK-3 C-terminal regions.
• Assessment of COPI binding in response to phosphorylation of the trafficking control region.

Main Results:

• Phosphorylation of the trafficking control region inhibits COPI binding, independent of 14-3-3 proteins.
• 14-3-3 protein affinities for TASK-1 were significantly lower (two orders of magnitude) than for TASK-3.
• Phosphorylation of a distinct serine residue in TASK-1's C-terminus inhibits 14-3-3 binding.

Conclusions:

• Phosphorylation of the TASK-1 trafficking control region can either stimulate or inhibit cell surface transport, depending on the specific serine residue targeted.
• The regulation of TASK-1 trafficking by COPI, kinases, phosphatases, and 14-3-3 proteins is a highly dynamic process.