Elimination of protein kinase MK5/PRAK activity by targeted homologous recombination

Area of Science:

• Molecular Biology
• Immunology
• Cell Signaling

Background:

• Mitogen-activated protein kinase (MAPK)-activated protein kinase 5 (MK5), also known as PRAK, is structurally similar to MK2.
• Previous studies suggested potential functional overlap between MK5 and MK2 in cellular signaling pathways.

Purpose of the Study:

• To investigate the in vivo function of MK5 by generating and characterizing MK5 knockout mice.
• To elucidate the mechanistic differences between MK5 and MK2, explaining their distinct physiological roles.

Main Methods:

• Homologous recombination was used to generate MK5 knockout mice.
• Phenotypic analysis of MK5 knockout mice, including assessment of viability, fertility, tissue morphology, behavior, and response to endotoxic shock.
• Biochemical assays using wild-type and knockout mouse embryonic fibroblasts to examine p38 MAPK interaction, activation mechanisms, and substrate specificity (e.g., Hsp27 phosphorylation) for both MK2 and MK5.

Main Results:

• MK5 knockout mice were viable and fertile with no observable abnormalities in morphology or behavior.
• MK5 deficiency did not confer resistance to endotoxic shock or alter lipopolysaccharide-induced cytokine production.
• Endogenous MK5 did not interact with or chaperone p38 MAPK, nor was it activated by extracellular stresses like MK2.
• MK5 failed to phosphorylate Hsp27 in vitro and in vivo, a known substrate for MK2.

Conclusions:

• MK5 plays a distinct role compared to MK2, as evidenced by the lack of significant phenotype in MK5 knockout mice.
• The functional differences stem from MK5's inability to interact with p38 MAPK and phosphorylate key substrates like Hsp27, unlike MK2.
• These findings clarify the non-redundant functions of MK5 and MK2 in cellular signaling and inflammatory responses.