Functional characterisation of a novel class of in-frame insertion variants of KRAS and HRAS

Area of Science:

• Molecular Biology
• Genetics
• Biochemistry

Background:

• Mutations in RAS genes are implicated in various conditions, including oncology, RASopathies, and vascular malformations.
• Typically, RAS gene mutations involve single amino acid substitutions causing constitutive signaling due to increased GTP-bound RAS proteins.

Purpose of the Study:

• To characterize a novel class of RAS variants involving in-frame insertions and duplications.
• To investigate the functional impact of these variants on RAS protein activity and signaling.

Main Methods:

• Identification of variants through routine diagnostic screening of samples for RASopathies and vascular malformations.
• Biophysical characterization of variant proteins to assess GTP loading and hydrolysis.
• Analysis of RAS signaling in a cellular model system.

Main Results:

• Seven in-frame insertions/duplications in HRAS and KRAS were identified, inserting 7-10 amino acids in the switch II region.
• These variants exhibited impaired Guanine Nucleotide Exchange Factor-induced GTP loading and reduced GTP hydrolysis.
• Cellular models demonstrated increased RAS signaling in the presence of these variants.

Conclusions:

• In-frame insertions and duplications in RAS genes represent a new class of weakly activating variants.
• These findings expand the spectrum of clinically relevant RAS mutations and their underlying mechanisms.