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An unexpected new role of mutant Ras: perturbation of human embryonic development

Christian P Kratz1, Charlotte M Niemeyer, Martin Zenker

  • 1Division of Pediatric Hematology and Oncology, Department of Pediatrics and Adolescent Medicine, University of Freiburg, Mathildenstrasse 1, 79106, Freiburg, Germany. christian.kratz@uniklinik-freiburg.de

Journal of Molecular Medicine (Berlin, Germany)
|January 11, 2007
PubMed

Insights

Germline mutations in the KRAS gene cause Noonan and cardio-facio-cutaneous syndromes by constitutively activating the Ras signaling pathway. These mutations lead to developmental abnormalities, unlike more severe cancer-associated RAS mutations.

Area of Science:

  • Molecular Biology
  • Genetics
  • Developmental Biology

Background:

  • The Ras signaling pathway is crucial for cellular responses to growth factors and is frequently altered in human cancers via somatic mutations in RAS genes and related proteins like PTPN11 and BRAF.
  • Ras proteins function as molecular switches, cycling between active GTP-bound and inactive GDP-bound states. Their intrinsic GTPase activity is vital for inactivation.
  • Somatic mutations in RAS genes, often at key residues like G12, G13, or Q61, significantly reduce GTPase activity, leading to constitutive Ras activation in neoplasia.

Purpose of the Study:

  • To investigate the role of germline mutations in the KRAS gene in developmental disorders.
  • To understand the biochemical basis of Ras pathway activation in Noonan and cardio-facio-cutaneous (CFC) syndromes.
  • To elucidate the connection between Ras pathway dysregulation and the characteristic features of Noonan-like disorders.

Main Methods:

  • Identification and characterization of germline mutations in the KRAS gene.
  • Biochemical analysis of Ras protein activity in response to specific mutations (e.g., V14I and T58I in K-Ras).
  • Comparison of the effects of germline mutations with somatic mutations found in cancers.

Main Results:

  • Germline mutations in KRAS were identified in individuals with Noonan and CFC syndromes.
  • Noonan syndrome-associated K-Ras mutations (V14I, T58I) lead to Ras activation with milder biochemical effects compared to cancer-associated somatic mutations.
  • These milder effects explain the tolerance of these mutations during embryonic development.

Conclusions:

  • Germline mutations in KRAS and other Ras pathway components (BRAF, MEK1/2, HRAS) underlie Noonan, CFC, and Costello syndromes.
  • Constitutive activation of the Ras-Raf-extracellular signal-regulated kinase (ERK) and mitogen-activated protein kinase (MAPK) pathway is the common mechanism driving the Noonan-like features observed in these related disorders.
  • Understanding these germline mutations provides insight into developmental biology and the spectrum of Ras pathway-related disorders.

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