Activation of H-ras61L-specific signaling pathways does not require posttranslational processing of H-ras

Area of Science:

• Molecular Biology
• Cell Biology
• Biochemistry

Background:

• Ras proteins require C-terminal lipid modifications for proper plasma membrane localization and function.
• Previous work showed H-ras61L retains transforming activity when lipid modifications are absent if localized to the plasma membrane via an N-terminal transmembrane domain.
• Ras-activated pathways contribute to cellular transformation.

Purpose of the Study:

• To investigate whether lipid modifications are essential for the activation of specific Ras-dependent signaling pathways.
• To examine the role of C-terminal lipid modifications in H-ras61L signaling.
• To determine if plasma membrane targeting via a transmembrane domain is sufficient for pathway activation.

Main Methods:

• Utilized novel transmembrane domain-anchored H-ras derivatives.
• Performed biochemical fractionation to confirm plasma membrane localization.
• Assessed activation of Raf/MEK/MAPK, Rac/Rho, and PI 3-kinase pathways.
• Evaluated downstream events like c-fos induction and neurite outgrowth.

Main Results:

• H-ras61L-induced activation of the Raf/MEK/MAPK pathway occurs without C-terminal lipid modifications.
• Recruitment of Raf to the plasma membrane and activation of Raf and MAPK are independent of lipid modifications.
• Plasma membrane-anchored, nonlipidated H-ras61L activates Rac/Rho and PI 3-kinase pathways.
• Downstream effects such as c-fos induction and neurite outgrowth are stimulated by nonlipidated H-ras61L.

Conclusions:

• H-ras can be functionally targeted to the plasma membrane using a transmembrane domain sequence.
• Several signal transduction pathways downstream of H-ras can be activated without normal lipid modifications.
• C-terminal lipid modifications are not universally required for H-ras signaling to key pathways.