MAP4K4 Is a Threonine Kinase That Phosphorylates FARP1.

Area of Science:

• Cell Biology
• Molecular Biology
• Biochemistry

Background:

• Mitogen-activated protein kinase 4 (MAP4K4) is involved in the MEK kinase cascade, cytoskeletal rearrangement, and cell migration.
• Identifying direct substrates of MAP4K4 has been a significant challenge in understanding its cellular functions.

Purpose of the Study:

• To identify MAP4K4-dependent phosphorylation events in cells.
• To determine the kinase specificity of MAP4K4.
• To investigate the relationship between MAP4K4 and FARP1 in cellular processes.

Main Methods:

• Combined phosphoproteomic analysis of MAP4K4 inhibition with in vitro kinase specificity assays.
• Investigated the interaction and phosphorylation of FARP1 by MAP4K4.
• Assessed the effect of MAP4K4 inhibition on neurite outgrowth in SH-SY5Y cells.

Main Results:

• Identified 235 phosphosites affected by MAP4K4 inhibition, with a predominance of pTP and pSP motifs.
• Demonstrated that MAP4K4 favors a pTL motif in vitro.
• Showed that MAP4K4 directly phosphorylates and coimmunoprecipitates with FARP1.
• Found that MAP4K4 inhibition increases neurite outgrowth in SH-SY5Y cells.

Conclusions:

• MAP4K4 directly phosphorylates FARP1, a protein involved in cytoskeletal rearrangement.
• MAP4K4 may regulate cytoskeletal dynamics, including neurite outgrowth, through its phosphorylation of FARP1.
• This study elucidates a novel substrate and mechanism for MAP4K4 signaling in cellular processes.