Germline mutations in components of the Ras signaling pathway in Noonan syndrome and related disorders
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Christian P Kratz1, Suzanne Schubbert, Gideon Bollag
1Division of Pediatric Hematology and Oncology, Department of Pediatrics and Adolescent Medicine, University of Freiburg, Freiburg, Germany. christian.kratz@uniklinik-freiburg.de
Abstract:
Ras proteins control a variety of critical cellular processes, and somatic mutations in RAS genes (and other members of signaling networks regulated by Ras) are common in human malignancies. Ras proteins are guanosine triphosphate (GTP)-binding proteins that cycle between active GTP-bound and inactive guanosine diphosphate (GDP) bound conformations. Cancer-associated Ras mutations typically alter amino acids G12, G13 or Q61. These mutant Ras proteins display impaired GTPase activity and are resistant to GTPase activating proteins (GAPs). We and others recently discovered novel germline KRAS mutations in individuals diagnosed with Noonan or cardio-facio-cutanous (CFC) syndrome, two clinically overlapping disorders characterized by short stature, distinct facial anomalies, heart defects, and other developmental abnormalities. We found that the mutant K-Ras proteins encoded by NS-associated alleles have less pronounced biochemical defects than known Ras oncoproteins, which likely explains why these mutations are tolerated in the germline. Together with the recent findings of mutations in other members of the Ras signaling cascade in CFC syndrome and in Costello syndrome, another clinically related disorder, it is now clear that Noonan-like features are common phenotypic consequences of systemic deregulation of the Ras pathway. The discovery of germline mutations in this group of related genetic disorders underscores the pivotal role of the degree and duration of Ras activation in cell fate decisions during embryonic development and morphogenesis.
Insights
Germline KRAS mutations cause Noonan and related syndromes by altering Ras signaling during development. These mutations have milder biochemical effects than cancer-associated mutations, allowing germline inheritance.
Area of Science:
- Molecular Biology
- Genetics
- Developmental Biology
Background:
- Ras proteins are key regulators of cellular processes, with mutations implicated in cancer.
- Ras proteins cycle between active GTP-bound and inactive GDP-bound states.
- Somatic RAS mutations are frequent in malignancies, often affecting specific amino acids (G12, G13, Q61) and impairing GTPase activity.
Purpose of the Study:
- To investigate novel germline KRAS mutations identified in Noonan syndrome and cardio-facio-cutaneous (CFC) syndrome.
- To understand the biochemical properties of these germline mutations compared to cancer-associated mutations.
- To elucidate the role of Ras pathway dysregulation in developmental disorders.
Main Methods:
- Identification and characterization of novel germline KRAS mutations.
- Biochemical analysis of mutant K-Ras protein activity, including GTPase activity and GAP interaction.
- Comparison of biochemical defects between germline and somatic Ras mutations.
Main Results:
- Novel germline KRAS mutations were discovered in individuals with Noonan and CFC syndromes.
- Mutant K-Ras proteins from these germline mutations exhibit less severe biochemical defects than canonical Ras oncoproteins.
- These milder defects likely explain the germline tolerance of these mutations.
Conclusions:
- Germline mutations in KRAS and other Ras pathway components contribute to Noonan-like features and related developmental disorders.
- The degree and duration of Ras pathway activation are critical for embryonic development and morphogenesis.
- Systemic deregulation of the Ras pathway underlies a spectrum of related genetic disorders.
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