Cyclin-dependent kinase 5 activates guanine nucleotide exchange factor GIV/Girdin to orchestrate...

Area of Science:

• Cell Biology
• Molecular Biology
• Biochemistry

Background:

• Receptor tyrosine kinases (RTKs) signal through pathways that can promote cell migration or proliferation, but not simultaneously, a phenomenon known as the migration-proliferation dichotomy.
• Epidermal growth factor (EGF) signaling favors cell migration over proliferation via noncanonical transactivation of Gαi proteins by the guanine exchange factor (GEF) GIV.
• The upstream activators of GIV-GEF downstream of growth factor RTKs were previously unknown.

Purpose of the Study:

• To elucidate the molecular mechanism by which GIV-GEF is activated by growth factor receptor signaling.
• To identify the upstream kinase responsible for GIV-GEF activation.
• To understand how this activation establishes the migration-proliferation dichotomy.

Main Methods:

• Investigated the interaction between GIV and cyclin-dependent kinase 5 (CDK5).
• Utilized phosphorylation site mapping to identify the key residue (Ser1674) on GIV.
• Assessed the effects of GIV phosphorylation on Gαi and Gαs binding and activation.
• Analyzed downstream signaling pathways, including Akt and MAPK.
• Examined the impact on cell migration and proliferation in wound healing and cancer cell transmigration models.

Main Results:

• CDK5 directly binds and phosphorylates GIV at Ser1674, near its GEF motif.
• Phosphorylation of GIV at Ser1674 enables it to bind and activate Gαi, enhancing promigratory Akt signals.
• Phosphorylated GIV also binds Gαs, promoting endosomal maturation and limiting mitogenic MAPK signals by reducing epidermal growth factor receptor (EGFR) transit time.
• This phosphoevent directs cells towards migration during wound healing and cancer cell invasion.
• Failure to phosphorylate Ser1674 prevents GIV binding to Gαi and Gαs, suppresses Akt signaling, enhances MAPK signaling due to delayed EGFR transit, and promotes proliferation.

Conclusions:

• GIV-GEF activation is triggered by CDK5-mediated phosphorylation at Ser1674 in response to growth factors.
• This phosphorylation event is a critical switch that orchestrates the migration-proliferation dichotomy.
• The findings reveal a novel mechanism involving CDK5 and GIV in regulating cell movement and division, with implications for cancer invasion, wound healing, and development.