Both p16 ^Ink4a and the p19 ^Arf -p53 pathway constrain progression of pancreatic adenocarcinoma in the mouse

Abstract

Activating KRAS mutations and p16 Ink4a inactivation are near universal events in human pancreatic ductal adenocarcinoma (PDAC). In mouse models, Kras G12D initiates formation of premalignant pancreatic ductal lesions, and loss of either Ink4a͞Arf (p16 Ink4a ͞p19 Arf ) or p53 enables their malignant progression. As recent mouse modeling studies have suggested a less prominent role for p16 Ink4a in constraining malignant progression, we sought to assess the pathological and genomic impact of inactivation of p16 Ink4a , p19 Arf , and͞or p53 in the Kras G12D model. Rapidly progressive PDAC was observed in the setting of homozygous deletion of either p53 or p16 Ink4a , the latter with intact germ-line p53 and p19 Arf sequences. Additionally, Kras G12D in the context of heterozygosity either for p53 plus p16 Ink4a or for p16 Ink4a ͞p19 Arf produced PDAC with longer latency and greater propensity for distant metastases relative to mice with homozygous deletion of p53 or p16 Ink4a ͞p19 Arf . Tumors from the double-heterozygous cohorts showed frequent p16 Ink4a inactivation and loss of either p53 or p19 Arf . Different genotypes were associated with specific histopathologic characteristics, most notably a trend toward less differentiated features in the homozygous p16 Ink4a ͞p19 Arf mutant model. High-resolution genomic analysis revealed that the tumor suppressor genotype influenced the specific genomic patterns of these tumors and showed overlap in regional chromosomal alterations between murine and human PDAC. Collectively, our results establish that disruptions of p16 Ink4a and the p19 ARF -p53 circuit play critical and cooperative roles in PDAC progression, with specific tumor suppressor genotypes provocatively influencing the tumor biological phenotypes and genomic profiles of the resultant tumors.array comparative genomic hybridization ͉ mouse models ͉ pancreatic cancer ͉ KRAS ͉ tumor suppressor P ancreatic ductal adenocarcinoma (PDAC) ranks as the fourth leading cause of cancer mortality in the United States and causes Ͼ200,000 deaths worldwide annually (1, 2). Histopathological analyses have identified precursor lesions, pancreatic intraepithelial neoplasias (PanIN), which appear to progress through increasingly severe stages of cellular atypia leading to invasive PDAC (3). These lesions show multistep molecular progression that includes early activating KRAS mutations and telomere attrition, and subsequent inactivation of p16 Ink4a , p14 ARF , p53, and͞or SMAD4 tumor suppressors in a high percentage of cases (4-6).The Ink4a͞Arf locus (hereafter denoted p16 Ink4a ͞p19 Arf ) encodes tumor suppressors p16 INK4A and p14 ARF (p19 Arf in the mouse). p16 INK4A is a G 1 cyclin-dependent kinase (CDK) inhibitor that binds to CDK4 and CDK6 and prevents their association with D-type cyclins (7), thereby facilitating CDK4͞6-cyclin D-mediated phosphorylation and inactivation of retinoblastoma protein (RB) and S-phase entry. p16 INK4A -mediated tumor suppression may relate to its induction by activated oncogenes and consequen...

TAp73 loss favors Smad-independent TGF-β signaling that drives EMT in pancreatic ductal adenocarcinoma

“…These data were confirmed using the CKIH mice (Pdx1-Cre/ LSL-Kras G12D /Ink4a/Arf F/+ ) (Supplementary Figure S2b). Similarly to the original study, 27 CKIH mice developed PDA with a longer latency of 227 days compared with the 66 days of CKI mice (Supplementary Figure S2c; n = 19 and 9, respectively, Po0.0001), and combination with TA mice shortened the latency of CKIH mice from 227 to 169 days for CKIHTA (Figure 1g; n = 9 and 8, respectively, P = 0.035). Altogether, with similar clinical representation across the various PDA models, these data reveal that, as reported for the PDA mouse model carrying a loss of TP53, TAp73 functions as a potent barrier to PDA progression.…”

“…Interestingly, PDA developed in this homozygous-null TAp73 model showed similar histology as well as close progression kinetic to that observed in TP53 − / − background, with a median lethality of 50 days. 27 These data suggest that while both act in limiting PDA development, p53 and TAp73 showed no compensatory activity in this physiological context. These data were confirmed using the CKIH mice (Pdx1-Cre/ LSL-Kras G12D /Ink4a/Arf F/+ ) (Supplementary Figure S2b).…”

Tumor escape in a Wnt1-dependent mouse breast cancer model is enabled by p19Arf/p53 pathway lesions but not p16Ink4a loss

“…Notably, even introducing a single null Ink4a/Arf allele accelerated Myc-initiated lymphomagenesis, and lymphomas generated in Ink4a/Arf +/-mice invariably were rendered functionally null via LOH, whereas mammary tumors arising in Ink4a/Arf +/-mice in our study routinely retained the wild-type allele. Likewise, both Ras-initiated melanomas (42) and pancreatic cancers (43) are accelerated when either Ink4a/Arf-encoded gene product is deleted, and this is especially so in the setting of combined Ink4a/Arf deficiency. Differences in the transgenes (Wnt vs. Myc/Ras) and/or tissues analyzed in each study may explain the distinct consequences of Ink4a/Arf loss in these models.…”

p16Ink4a overexpression in cancer: a tumor suppressor gene associated with senescence and high-grade tumors

“…Pancreatic carcinomas constitute the paradigm of tumors presenting p16 Ink4a inactivation, with 98% of cases showing a loss of p16 Ink4a function (Moore et al, 2001a, b;Fukushima et al, 2002;Bardeesy et al, 2006). In these tumors, several mechanisms whereby the p16 Ink4a gene is inactivated have been described, including homozygotic deletions, loss of heterozygosity, point mutations and promoter methylation (Herman et al, 1995;Rutter et al, 2003;Paulson et al, 2008;Andujar et al, 2010).…”