RESUMEN
Monitoring cancer and aging in vivo remains experimentally challenging. Here, we describe a luciferase knockin mouse (p16(LUC)), which faithfully reports expression of p16(INK4a), a tumor suppressor and aging biomarker. Lifelong assessment of luminescence in p16(+/LUC) mice revealed an exponential increase with aging, which was highly variable in a cohort of contemporaneously housed, syngeneic mice. Expression of p16(INK4a) with aging did not predict cancer development, suggesting that the accumulation of senescent cells is not a principal determinant of cancer-related death. In 14 of 14 tested tumor models, expression of p16(LUC) was focally activated by early neoplastic events, enabling visualization of tumors with sensitivity exceeding other imaging modalities. Activation of p16(INK4a) was noted in the emerging neoplasm and surrounding stromal cells. This work suggests that p16(INK4a) activation is a characteristic of all emerging cancers, making the p16(LUC) allele a sensitive, unbiased reporter of neoplastic transformation.
Asunto(s)
Envejecimiento/genética , Biomarcadores , Transformación Celular Neoplásica , Inhibidor p16 de la Quinasa Dependiente de Ciclina/genética , Luciferasas/genética , Neoplasias/genética , Animales , Senescencia Celular , Inhibidor p16 de la Quinasa Dependiente de Ciclina/metabolismo , Femenino , Técnicas de Sustitución del Gen , Ratones , Neoplasias/fisiopatología , Heridas y Lesiones/genéticaRESUMEN
B cell lymphoma and melanoma harbor recurrent mutations in the gene encoding the EZH2 histone methyltransferase (EZH2), but the carcinogenic role of these mutations is unclear. Here we describe a mouse model in which the most common somatic Ezh2 gain-of-function mutation (EZH2(Y646F) in human; Ezh2(Y641F) in mouse) is conditionally expressed. Expression of Ezh2(Y641F) in mouse B cells or melanocytes caused high-penetrance lymphoma or melanoma, respectively. Overexpression of the anti-apoptotic protein Bcl2, but not the oncoprotein Myc, or loss of the tumor suppressor protein p53 (encoded by Trp53 in mice) further accelerated lymphoma progression. Expression of the mutant Braf but not the mutant Nras oncoprotein further accelerated melanoma progression. Although expression of Ezh2(Y641F) globally increased the abundance of trimethylated Lys27 of histone H3 (H3K27me3), it also caused a widespread redistribution of this repressive mark, including a loss of H3K27me3 that was associated with increased transcription at many loci. These results suggest that Ezh2(Y641F) induces lymphoma and melanoma through a vast reorganization of chromatin structure, inducing both repression and activation of polycomb-regulated loci.
Asunto(s)
Carcinogénesis/genética , Proteína Potenciadora del Homólogo Zeste 2/genética , Regulación Neoplásica de la Expresión Génica/genética , Código de Histonas/genética , Linfoma de Células B/genética , Melanoma/genética , Animales , Linfocitos B/metabolismo , Línea Celular Tumoral , Progresión de la Enfermedad , Técnicas de Silenciamiento del Gen , Humanos , Immunoblotting , Melanocitos/metabolismo , Metilación , Ratones , Proteínas de Unión al GTP Monoméricas/genética , Mutación , Trasplante de Neoplasias , Proteínas Proto-Oncogénicas B-raf/genética , Proteínas Proto-Oncogénicas c-bcl-2/genética , Proteínas Proto-Oncogénicas c-myc/genética , Reacción en Cadena en Tiempo Real de la Polimerasa , Proteína p53 Supresora de Tumor/genéticaRESUMEN
UNLABELLED: NRAS mutation at codons 12, 13, or 61 is associated with transformation; yet, in melanoma, such alterations are nearly exclusive to codon 61. Here, we compared the melanoma susceptibility of an NrasQ61R knock-in allele to similarly designed KrasG12D and NrasG12D alleles. With concomitant p16INK4a inactivation, KrasG12D or NrasQ61R expression efficiently promoted melanoma in vivo, whereas NrasG12D did not. In addition, NrasQ61R mutation potently cooperated with Lkb1/Stk11 loss to induce highly metastatic disease. Functional comparisons of NrasQ61R and NrasG12D revealed little difference in the ability of these proteins to engage PI3K or RAF. Instead, NrasQ61R showed enhanced nucleotide binding, decreased intrinsic GTPase activity, and increased stability when compared with NrasG12D. This work identifies a faithful model of human NRAS-mutant melanoma, and suggests that the increased melanomagenecity of NrasQ61R over NrasG12D is due to heightened abundance of the active, GTP-bound form rather than differences in the engagement of downstream effector pathways. SIGNIFICANCE: This work explains the curious predominance in human melanoma of mutations of codon 61 of NRAS over other oncogenic NRAS mutations. Using conditional "knock-in" mouse models, we show that physiologic expression of NRASQ61R, but not NRASG12D, drives melanoma formation.