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Dual inactivation of RB and p53 pathways in RAS-induced melanomas
N Bardeesy1, B C Bastian, A Hezel
1Department of Adult Oncology, Dana-Farber Cancer Institute, Harvard Medical School, Boston, Massachusetts 02115, USA.
Abstract:
The frequent loss of both INK4a and ARF in melanoma raises the question of which INK4a-ARF gene product functions to suppress melanoma genesis in vivo. Moreover, the high incidence of INK4a-ARF inactivation in transformed melanocytes, along with the lack of p53 mutation, implies a cell type-specific role for INK4a-ARF that may not be complemented by other lesions of the RB and p53 pathways. A mouse model of cutaneous melanoma has been generated previously through the combined effects of INK4a(Delta2/3) deficiency (null for INK4a and ARF) and melanocyte-specific expression of activated RAS (tyrosinase-driven H-RAS(V12G), Tyr-RAS). In this study, we made use of this Tyr-RAS allele to determine whether activated RAS can cooperate with p53 loss in melanoma genesis, whether such melanomas are biologically comparable to those arising in INK4a(Delta2/3-/-) mice, and whether tumor-associated mutations emerge in the p16(INK4a)-RB pathway in such melanomas. Here, we report that p53 inactivation can cooperate with activated RAS to promote the development of cutaneous melanomas that are clinically indistinguishable from those arisen on the INK4a(Delta2/3) null background. Genomewide analysis of RAS-induced p53 mutant melanomas by comparative genomic hybridization and candidate gene surveys revealed alterations of key components governing RB-regulated G(1)/S transition, including c-Myc, cyclin D1, cdc25a, and p21(CIP1). Consistent with the profile of c-Myc dysregulation, the reintroduction of p16(INK4a) profoundly reduced the growth of Tyr-RAS INK4a(Delta2/3-/-) tumor cells but had no effect on tumor cells derived from Tyr-RAS p53(-/-) melanomas. Together, these data validate a role for p53 inactivation in melanomagenesis and suggest that both the RB and p53 pathways function to suppress melanocyte transformation in vivo in the mouse.
Insights
Loss of p53 function cooperates with activated RAS to drive melanoma development, similar to INK4a/ARF loss. Both RB and p53 pathways suppress melanocyte transformation, highlighting their roles in melanoma genesis.
Area of Science:
- Oncology
- Molecular Biology
- Genetics
Background:
- Frequent loss of INK4a and ARF in melanoma suggests a critical role in tumor suppression.
- Melanoma development often involves inactivation of cell cycle regulators like p16INK4a and p53.
- A mouse model combining activated RAS and INK4a/ARF deficiency exists for studying melanoma genesis.
Purpose of the Study:
- To investigate if p53 loss cooperates with activated RAS in melanoma development.
- To compare melanomas arising from p53 loss with those from INK4a/ARF deficiency.
- To identify mutations in the RB pathway within RAS-induced p53 mutant melanomas.
Main Methods:
- Utilized a mouse model with melanocyte-specific activated RAS (Tyr-RAS) and either p53 deficiency or INK4a/ARF deficiency.
- Generated and characterized cutaneous melanomas in these mouse models.
- Performed genomewide analysis (CGH) and candidate gene surveys on tumor DNA.
- Assessed the impact of p16INK4a reintroduction on tumor cell growth.
Main Results:
- p53 inactivation cooperated with activated RAS to produce clinically indistinguishable melanomas compared to INK4a/ARF-deficient mice.
- RAS-induced p53 mutant melanomas showed alterations in RB pathway components (c-Myc, cyclin D1, cdc25a, p21CIP1).
- Reintroduction of p16INK4a inhibited Tyr-RAS INK4a(Delta2/3-/-) tumor growth but not Tyr-RAS p53(-/-) tumor growth.
Conclusions:
- p53 inactivation is validated as a crucial event in melanoma genesis.
- Both RB and p53 pathways are essential for suppressing melanocyte transformation in vivo.
- These findings provide insights into the genetic landscape of melanoma and potential therapeutic targets.