RIT1 controls actin dynamics via complex formation with RAC1/CDC42 and PAK1

Area of Science:

• Molecular Biology
• Cell Biology
• Genetics

Background:

• RIT1 is a RAS family small GTPase.
• RIT1 mutations are linked to Noonan syndrome and cancer.
• The precise function of RIT1 in cellular processes remains incompletely understood.

Purpose of the Study:

• To identify direct effectors of RIT1.
• To investigate the role of RIT1 in regulating actin dynamics and cell motility.
• To explore the functional consequences of RIT1 mutations.

Main Methods:

• Heterologous expression systems and purified recombinant proteins were used.
• Protein-protein interactions were assessed.
• Cytoskeletal rearrangements were analyzed via microscopy.
• Cell migration was evaluated using transwell assays.

Main Results:

• p21-activated kinase 1 (PAK1) was identified as a novel direct RIT1 effector.
• RIT1 directly interacts with RHO GTPases CDC42 and RAC1, independent of guanine nucleotide binding.
• Disease-associated RIT1 mutations enhance interactions with PAK1, CDC42, and RAC1, uncoupling complex formation from growth factor signaling.
• RIT1-PAK1 complex formation regulates cytoskeletal rearrangements, including stress fiber dissolution and focal adhesion reduction.
• RIT1, including disease variants, enhances cell motility.

Conclusions:

• RIT1 functions in a signaling module with PAK1 and RAC1/CDC42 to control actin dynamics.
• Defects in cell adhesion and migration due to aberrant RIT1 signaling are potential mechanisms underlying Noonan syndrome.
• This study reveals a new role for RIT1 in regulating cell adhesion and motility.