MAPKAP kinase 2 blocks tristetraprolin-directed mRNA decay by inhibiting CAF1 deadenylase recruitment

Area of Science:

• Molecular Biology
• Gene Regulation
• RNA Metabolism

Background:

• Tristetraprolin (TTP) promotes mRNA degradation by deadenylation of AU-rich element (ARE)-containing mRNAs.
• The p38 MAPK pathway, via MAPK-activated protein kinase 2 (MK2), regulates mRNA stability by inhibiting TTP's function through phosphorylation.

Purpose of the Study:

• To investigate if MK2 phosphorylation of TTP regulates TTP-directed deadenylation of ARE-containing mRNAs.
• To identify the deadenylase complex responsible for TTP-mediated deadenylation.
• To elucidate the mechanism by which MK2 phosphorylation affects TTP's deadenylation activity.

Main Methods:

• Cell-free assay to reconstitute TTP-directed deadenylation.
• Phosphorylation of TTP by MK2 using recombinant proteins.
• Use of 14-3-3 protein antagonists.
• Identification of deadenylase complexes using HeLa cell extracts.
• RNA-independent interaction studies between TTP and CAF1.

Main Results:

• MK2 phosphorylation of TTP at Ser-52 and Ser-178 inhibits TTP-directed deadenylation of ARE-containing RNA.
• The CCR4.CAF1 complex is the primary deadenylase responsible for TTP-directed deadenylation in HeLa cells.
• MK2 phosphorylation reduces TTP's deadenylation activity by inhibiting CAF1 recruitment, independent of 14-3-3 binding.
• Cyclooxygenase-2 mRNA stability increases in CAF1-depleted cells, losing p38 MAPK/MK2 regulation.

Conclusions:

• MK2 phosphorylation of TTP inhibits deadenylation by preventing CAF1 deadenylase recruitment.
• This phosphorylation-dependent regulation of TTP activity by MK2 is crucial for controlling the stability of ARE-containing mRNAs.
• The CCR4.CAF1 complex is a key effector of TTP in mRNA decay pathways.