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The BRAF kinase domain promotes the development of gliomas in vivo.

Shin CH, Grossmann AH, Holmen SL, Robinson JP - Genes Cancer (2015)

Bottom Line: They also lacked the necrosis and vascular proliferation seen in BRAFV600E-driven tumors.The BRAF-KD-expressing astrocytes showed elevated MAPK signaling, albeit at reduced levels compared to the BRAF(V600E) mutant.Pharmacologic inhibition of MEK and PI3K inhibited cell growth and induced apoptosis in astrocytes expressing BRAF-KD.

View Article: PubMed Central - PubMed

Affiliation: Huntsman Cancer Institute, University of Utah Health Sciences Center, Salt Lake City, Utah, USA ; Department of Oncological Sciences, University of Utah Health Sciences Center, Salt Lake City, Utah, USA.

ABSTRACT
In-frame BRAF fusions have been observed in over 80% of sporadic pilocytic astrocytomas. In each fusion, the N-terminal autoinhibitory domain of BRAF is lost, which results in constitutive activation via the retained C-terminal kinase domain (BRAF-KD). We set out to determine if the BRAF-KD is sufficient to induce gliomas alone or in combination with Ink4a/Arf loss. Syngeneic cell lines demonstrated the transforming ability of the BRAF-KD following Ink4a/Arf loss. In vivo, somatic cell gene transfer of the BRAF-KD did not cause tumors to develop; however, gliomas were detected in 21% of the mice following Ink4a/Arf loss. Interestingly, these mice demonstrated no obvious symptoms. Histologically the tumors were highly cellular and atypical, similar to BRAF(V600E) tumors reported previously, but with less invasive borders. They also lacked the necrosis and vascular proliferation seen in BRAFV600E-driven tumors. The BRAF-KD-expressing astrocytes showed elevated MAPK signaling, albeit at reduced levels compared to the BRAF(V600E) mutant. Pharmacologic inhibition of MEK and PI3K inhibited cell growth and induced apoptosis in astrocytes expressing BRAF-KD. Our findings demonstrate that the BRAF-KD can cooperate with Ink4a/Arf loss to drive the development of gliomas and suggest that glioma development is determined by the level of MAPK signaling.

No MeSH data available.


Related in: MedlinePlus

BRAF SchematicA: BRAFV600E B: KIAA1549:BRAF C: FAM131B-BRAF, showing FAM131B amino acids D: BRAF-kinase domain (BRAF-KD), showing amino acids of the HA epitope Tag. RBD=Ras binding domain.
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Figure 1: BRAF SchematicA: BRAFV600E B: KIAA1549:BRAF C: FAM131B-BRAF, showing FAM131B amino acids D: BRAF-kinase domain (BRAF-KD), showing amino acids of the HA epitope Tag. RBD=Ras binding domain.

Mentions: In each fusion the N-terminus of RAF is replaced by FAM131B, SRGAP3 or KIAA1549 resulting in loss of the N-terminal autoinhibitory domain of RAF and constitutive activation of the MAPK pathway via the retained C-terminal kinase domain (BRAF-KD) (Figure 1). The specificity with which the C-terminus of RAF fuses to these different genes suggests that it is required for tumorigenesis in this context; however, the role of the C-terminal domain of BRAF within the fusions in glioma formation has not been validated. Expression of a BRAF kinase domain mutant carrying the V600E alteration (BRAF-KDVE) was sufficient to induce PA-like lesions in mice [11]. However, in patients, the BRAF kinase domain has not been found to be mutated in this manner in the context of a fusion gene. V600E mutations in full length BRAF are seen in a small percentage of PA (6%) [9,12–14]; however, they are much more common in grade II, and high grade malignant pediatric gliomas; accounting for 18% of grade II, 33% of grade III, and 18% of grade IV tumors (23% grades II-IV) [15]. We have previously demonstrated that BRAFV600E can cooperate with Ink4a/Arf loss to induce high-grade gliomas in mice [16].


The BRAF kinase domain promotes the development of gliomas in vivo.

Shin CH, Grossmann AH, Holmen SL, Robinson JP - Genes Cancer (2015)

BRAF SchematicA: BRAFV600E B: KIAA1549:BRAF C: FAM131B-BRAF, showing FAM131B amino acids D: BRAF-kinase domain (BRAF-KD), showing amino acids of the HA epitope Tag. RBD=Ras binding domain.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4362480&req=5

Figure 1: BRAF SchematicA: BRAFV600E B: KIAA1549:BRAF C: FAM131B-BRAF, showing FAM131B amino acids D: BRAF-kinase domain (BRAF-KD), showing amino acids of the HA epitope Tag. RBD=Ras binding domain.
Mentions: In each fusion the N-terminus of RAF is replaced by FAM131B, SRGAP3 or KIAA1549 resulting in loss of the N-terminal autoinhibitory domain of RAF and constitutive activation of the MAPK pathway via the retained C-terminal kinase domain (BRAF-KD) (Figure 1). The specificity with which the C-terminus of RAF fuses to these different genes suggests that it is required for tumorigenesis in this context; however, the role of the C-terminal domain of BRAF within the fusions in glioma formation has not been validated. Expression of a BRAF kinase domain mutant carrying the V600E alteration (BRAF-KDVE) was sufficient to induce PA-like lesions in mice [11]. However, in patients, the BRAF kinase domain has not been found to be mutated in this manner in the context of a fusion gene. V600E mutations in full length BRAF are seen in a small percentage of PA (6%) [9,12–14]; however, they are much more common in grade II, and high grade malignant pediatric gliomas; accounting for 18% of grade II, 33% of grade III, and 18% of grade IV tumors (23% grades II-IV) [15]. We have previously demonstrated that BRAFV600E can cooperate with Ink4a/Arf loss to induce high-grade gliomas in mice [16].

Bottom Line: They also lacked the necrosis and vascular proliferation seen in BRAFV600E-driven tumors.The BRAF-KD-expressing astrocytes showed elevated MAPK signaling, albeit at reduced levels compared to the BRAF(V600E) mutant.Pharmacologic inhibition of MEK and PI3K inhibited cell growth and induced apoptosis in astrocytes expressing BRAF-KD.

View Article: PubMed Central - PubMed

Affiliation: Huntsman Cancer Institute, University of Utah Health Sciences Center, Salt Lake City, Utah, USA ; Department of Oncological Sciences, University of Utah Health Sciences Center, Salt Lake City, Utah, USA.

ABSTRACT
In-frame BRAF fusions have been observed in over 80% of sporadic pilocytic astrocytomas. In each fusion, the N-terminal autoinhibitory domain of BRAF is lost, which results in constitutive activation via the retained C-terminal kinase domain (BRAF-KD). We set out to determine if the BRAF-KD is sufficient to induce gliomas alone or in combination with Ink4a/Arf loss. Syngeneic cell lines demonstrated the transforming ability of the BRAF-KD following Ink4a/Arf loss. In vivo, somatic cell gene transfer of the BRAF-KD did not cause tumors to develop; however, gliomas were detected in 21% of the mice following Ink4a/Arf loss. Interestingly, these mice demonstrated no obvious symptoms. Histologically the tumors were highly cellular and atypical, similar to BRAF(V600E) tumors reported previously, but with less invasive borders. They also lacked the necrosis and vascular proliferation seen in BRAFV600E-driven tumors. The BRAF-KD-expressing astrocytes showed elevated MAPK signaling, albeit at reduced levels compared to the BRAF(V600E) mutant. Pharmacologic inhibition of MEK and PI3K inhibited cell growth and induced apoptosis in astrocytes expressing BRAF-KD. Our findings demonstrate that the BRAF-KD can cooperate with Ink4a/Arf loss to drive the development of gliomas and suggest that glioma development is determined by the level of MAPK signaling.

No MeSH data available.


Related in: MedlinePlus