Two Dictyostelium tyrosine kinase-like kinases function in parallel, stress-induced STAT activation pathways

Area of Science:

• Cellular signaling pathways
• Molecular mechanisms of stress response

Background:

• STATc activation by tyrosine phosphorylation is key in Dictyostelium hyperosmotic stress response.
• This activation is unusually regulated by serine phosphorylation, inhibiting the tyrosine phosphatase PTP3.

Purpose of the Study:

• Identify the unknown tyrosine kinase responsible for STATc activation.
• Investigate the roles of Pyk2 and Pyk3 in stress-induced STATc signaling.

Main Methods:

• Analysis of single and double null mutants for Pyk2 and Pyk3.
• Assessment of tyrosine phosphorylation in Pyk2 and Pyk3 under stress.
• Investigation of STATc SH2 domain binding to phosphorylated Pyk2/Pyk3.

Main Results:

• Pyk2 and Pyk3 were identified as the shared tyrosine kinases for STATc activation.
• Double mutants lacking both Pyk2 and Pyk3 showed complete impairment of stress-induced STATc activation.
• Pyk2 and Pyk3 exhibit increased autocatalytic tyrosine phosphorylation under stress, facilitating STATc binding and subsequent phosphorylation.
• Pyk3 possesses a pseudokinase domain regulating its kinase activity, similar to JAKs.

Conclusions:

• Pyk2 and Pyk3 are essential for stress-induced STATc activation in Dictyostelium.
• Differential cellular localization of Pyk2 and Pyk3 under stress suggests distinct regulatory roles.
• The dual kinase system provides a mechanism for precise targeting in cellular stress responses.