Differential AKT dependency displayed by mouse models of BRAFV600E-initiated melanoma
Victoria Marsh Durban, … , Wayne Phillips, Martin McMahon
Victoria Marsh Durban, … , Wayne Phillips, Martin McMahon
Published November 8, 2013
Citation Information: J Clin Invest. 2013;123(12):5104-5118. https://doi.org/10.1172/JCI69619.
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Research Article Oncology

Differential AKT dependency displayed by mouse models of BRAFV600E-initiated melanoma

Abstract

Malignant melanoma is frequently driven by mutational activation of v-raf murine sarcoma viral oncogene homolog B1 (BRAF) accompanied by silencing of the phosphatase and tensin homology (PTEN) tumor suppressor. Despite the implied importance of PI3K signaling in PTENNull melanomas, mutational activation of the gene encoding the catalytic subunit of PI3Kα (PIK3CA), is rarely detected. Since PTEN has both PI3-lipid phosphatase–dependent and –independent tumor suppressor activities, we investigated the contribution of PI3K signaling to BRAFV600E-induced melanomagenesis using mouse models, cultured melanoma cells, and PI3K pathway–targeted inhibitors. These experiments revealed that mutationally activated PIK3CAH1047R cooperates with BRAFV600E for melanomagenesis in mice. Moreover, pharmacological inhibition of PI3Ks prevented growth of BRAFV600E/PTENNull melanomas in vivo and in tissue culture. Combined inhibition of BRAFV600E and PI3K had more potent effects on the regression of established BRAFV600E/PTENNull melanomas and cultured melanoma cells than individual blockade of either pathway. Surprisingly, growth of BRAFV600E/PIK3CAH1047R melanomas was dependent on the protein kinase AKT; however, AKT inhibition had no effect on growth of BRAFV600E/PTENNull melanomas. These data indicate that PTEN silencing contributes a PI3K-dependent, but AKT-independent, function in melanomagenesis. Our findings enhance our knowledge of how BRAFV600E and PI3K signaling cooperate in melanomagenesis and provide preclinical validation for combined pathway–targeted inhibition of PI3K and BRAFV600E in the therapeutic management of BRAFV600E/PTENNull melanomas.

Authors

Victoria Marsh Durban, Marian M. Deuker, Marcus W. Bosenberg, Wayne Phillips, Martin McMahon

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Figure 3

AKT activity is required for BRAFV600E/PIK3CAH1047R but not BRAFV600E/PTENNull melanoma growth.

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AKT activity is required for BRAFV600E/PIK3CAH1047R but not BRAFV600E/PT...
BRAFV600E/PTENNull (A) or BRAFV600E/PIK3CAH1047R (B) melanoma growth was initiated, and 30 days later, treatment with vehicle control (+VEH) or with MK-2206, a pan-AKT inhibitor (+MK) was begun (BRAFV600E/PTENNull + VEH, n = 10; BRAFV600E/PTENNull + MK, n = 8; BRAFV600E/PIK3CAH1047R + VEH, n = 10, BRAFV600E/PIK3CAH1047R + MK, n = 10). Melanoma growth was visually assessed over the treatment time as described above. (C and D) Melanoma growth in the absence (VEH) or presence of AKT inhibitor (MK) was measured from 10–90 days after commencement of treatment. MK-2206–treated BRAFV600E/PTENNull melanomas were not significantly smaller than vehicle-treated controls at any time after initiation of drug treatment (Student’s 1-tailed t test, C). In contrast, BRAFV600E/PIK3CAH1047R melanomas were significantly smaller in MK-2206–treated mice compared with vehicle treated from day 76 of treatment onwards (*P < 0.01, Student’s 1-tailed t test, *P < 0.01, D). (E) BRAFV600E/PTENNull or BRAFV600E/PIK3CAH1047R melanomas from either vehicle- or MK-2206–treated mice were stained with H&E, anti-S100, or anti-Ki67 as indicated. Scale bars: 100 μm. (F) Tumor lysates obtained from vehicle- or MK-2206–treated BRAFV600E/PTENNull or BRAFV600E/PIK3CAH1047R melanomas were probed with backbone- or phospho-specific antisera against AKT or ERK1/2. β-Actin was used as a loading control.