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Activating K-Ras mutations outwith 'hotspot' codons in sporadic colorectal tumours - implications for personalised cancer medicine.

Smith G, Bounds R, Wolf H, Steele RJ, Carey FA, Wolf CR - Br. J. Cancer (2010)

Bottom Line: Colorectal tumours (n=106) were screened for additional K-Ras mutations, phenotypes compared in transformation and Ras GTPase activating assays and gene and pathway changes induced by individual K-Ras mutants identified by microarray analysis.The identification of mutations outwith previously described hotspot codons increases the K-Ras mutation burden in colorectal tumours by one-third.Future mutation screening to facilitate optimal patient selection for treatment with EGFR-targeted therapies should therefore be extended to codon 146, and in addition should consider the unique molecular signatures associated with individual K-Ras mutations.

View Article: PubMed Central - PubMed

Affiliation: Biomedical Research Institute, Ninewells Hospital and Medical School, Dundee, UK.

ABSTRACT

Background: Response to EGFR-targeted therapies in colorectal cancer patients has been convincingly associated with Kirsten-Ras (K-Ras) mutation status. Current mandatory mutation testing for patient selection is limited to the K-Ras 'hotspot' codons 12 and 13.

Methods: Colorectal tumours (n=106) were screened for additional K-Ras mutations, phenotypes compared in transformation and Ras GTPase activating assays and gene and pathway changes induced by individual K-Ras mutants identified by microarray analysis. Taqman-based gene copy number and FISH analyses were used to investigate K-Ras gene amplification.

Results: Four additional K-Ras mutations (Leu(19)Phe (1 out of 106 tumours), Lys(117)Asn (1 out of 106), Ala(146)Thr (7 out of 106) and Arg(164)Gln (1 out of 106)) were identified. Lys(117)Asn and Ala(146)Thr had phenotypes similar to the hotspot mutations, whereas Leu(19)Phe had an attenuated phenotype and the Arg(164)Gln mutation was phenotypically equivalent to wt K-Ras. We additionally identified a new K-Ras gene amplification event, present in approximately 2% of tumours.

Conclusions: The identification of mutations outwith previously described hotspot codons increases the K-Ras mutation burden in colorectal tumours by one-third. Future mutation screening to facilitate optimal patient selection for treatment with EGFR-targeted therapies should therefore be extended to codon 146, and in addition should consider the unique molecular signatures associated with individual K-Ras mutations.

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Related in: MedlinePlus

The Ras cycle. Ras proteins are key components of signal transduction pathways leading from cell-surface receptors to the control of cell proliferation, differentiation or death. Active Ras, where tumour-specific mutations lock Ras in the GTP-bound conformation, stimulates the RAS–RAF–MEK–ERK–MAP kinase signalling pathway.
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fig1: The Ras cycle. Ras proteins are key components of signal transduction pathways leading from cell-surface receptors to the control of cell proliferation, differentiation or death. Active Ras, where tumour-specific mutations lock Ras in the GTP-bound conformation, stimulates the RAS–RAF–MEK–ERK–MAP kinase signalling pathway.

Mentions: K-Ras is a member of the highly homologous family of small p21Ras G proteins (H-Ras, N-Ras and K-Ras) which transduce signals across the plasma membrane, principally by activation of the RAS–RAF–MEK–ERK–MAPK signalling cascade (Figure 1; (Barbacid, 1990)). Ras genes are the most frequently mutated oncogenes in human cancer, where tumour-specific mutations lead to the permanent activation of Ras signalling cascades, influencing proliferation, differentiation and apoptosis (Bos, 1989). Previous analyses of K-Ras mutations in human tumours have consistently focussed on single-point mutations in codons 12, 13 and 61, where mutation has been shown to result in reduced Ras GAP GTPase activity, locking the protein in the active Ras-GTP conformation (Ellis and Clark, 2000), although additional mutations at codons 19, 22 and 146 have been described in single colorectal tumour case reports (Orita et al, 1991; Miyakura et al, 2002; Akagi et al, 2007).


Activating K-Ras mutations outwith 'hotspot' codons in sporadic colorectal tumours - implications for personalised cancer medicine.

Smith G, Bounds R, Wolf H, Steele RJ, Carey FA, Wolf CR - Br. J. Cancer (2010)

The Ras cycle. Ras proteins are key components of signal transduction pathways leading from cell-surface receptors to the control of cell proliferation, differentiation or death. Active Ras, where tumour-specific mutations lock Ras in the GTP-bound conformation, stimulates the RAS–RAF–MEK–ERK–MAP kinase signalling pathway.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2837563&req=5

fig1: The Ras cycle. Ras proteins are key components of signal transduction pathways leading from cell-surface receptors to the control of cell proliferation, differentiation or death. Active Ras, where tumour-specific mutations lock Ras in the GTP-bound conformation, stimulates the RAS–RAF–MEK–ERK–MAP kinase signalling pathway.
Mentions: K-Ras is a member of the highly homologous family of small p21Ras G proteins (H-Ras, N-Ras and K-Ras) which transduce signals across the plasma membrane, principally by activation of the RAS–RAF–MEK–ERK–MAPK signalling cascade (Figure 1; (Barbacid, 1990)). Ras genes are the most frequently mutated oncogenes in human cancer, where tumour-specific mutations lead to the permanent activation of Ras signalling cascades, influencing proliferation, differentiation and apoptosis (Bos, 1989). Previous analyses of K-Ras mutations in human tumours have consistently focussed on single-point mutations in codons 12, 13 and 61, where mutation has been shown to result in reduced Ras GAP GTPase activity, locking the protein in the active Ras-GTP conformation (Ellis and Clark, 2000), although additional mutations at codons 19, 22 and 146 have been described in single colorectal tumour case reports (Orita et al, 1991; Miyakura et al, 2002; Akagi et al, 2007).

Bottom Line: Colorectal tumours (n=106) were screened for additional K-Ras mutations, phenotypes compared in transformation and Ras GTPase activating assays and gene and pathway changes induced by individual K-Ras mutants identified by microarray analysis.The identification of mutations outwith previously described hotspot codons increases the K-Ras mutation burden in colorectal tumours by one-third.Future mutation screening to facilitate optimal patient selection for treatment with EGFR-targeted therapies should therefore be extended to codon 146, and in addition should consider the unique molecular signatures associated with individual K-Ras mutations.

View Article: PubMed Central - PubMed

Affiliation: Biomedical Research Institute, Ninewells Hospital and Medical School, Dundee, UK.

ABSTRACT

Background: Response to EGFR-targeted therapies in colorectal cancer patients has been convincingly associated with Kirsten-Ras (K-Ras) mutation status. Current mandatory mutation testing for patient selection is limited to the K-Ras 'hotspot' codons 12 and 13.

Methods: Colorectal tumours (n=106) were screened for additional K-Ras mutations, phenotypes compared in transformation and Ras GTPase activating assays and gene and pathway changes induced by individual K-Ras mutants identified by microarray analysis. Taqman-based gene copy number and FISH analyses were used to investigate K-Ras gene amplification.

Results: Four additional K-Ras mutations (Leu(19)Phe (1 out of 106 tumours), Lys(117)Asn (1 out of 106), Ala(146)Thr (7 out of 106) and Arg(164)Gln (1 out of 106)) were identified. Lys(117)Asn and Ala(146)Thr had phenotypes similar to the hotspot mutations, whereas Leu(19)Phe had an attenuated phenotype and the Arg(164)Gln mutation was phenotypically equivalent to wt K-Ras. We additionally identified a new K-Ras gene amplification event, present in approximately 2% of tumours.

Conclusions: The identification of mutations outwith previously described hotspot codons increases the K-Ras mutation burden in colorectal tumours by one-third. Future mutation screening to facilitate optimal patient selection for treatment with EGFR-targeted therapies should therefore be extended to codon 146, and in addition should consider the unique molecular signatures associated with individual K-Ras mutations.

Show MeSH
Related in: MedlinePlus