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omal instability invivo. Similarly, mouse embryonic fibroblastsfrom CKB21111 mice, infected withadenoviralcre to rearrange the Brca2 and Kras loci, displayed elevated levelsof aneuploidy and multinucleation relative to MEFs from CX-4945 CKB2wtwt mice, in both thepresence and absence of KrasG12D. To evaluate no matter if the structuraland numerical chromosomal instability resulting from Brca2 deficiency resulted in elevatedlevels of cell death within the presence of Trp53 disruption and activated Kras, we measured invivo apoptosis by cleaved caspase 3 staining of acinar and ductal cells within the pancreas glandsof 4 month old mice. Levels of apoptosis were increased 2fold in CPB21111 mice relativeto CPB2wtwt mice, suggesting that the instability caused by absence of Brca2enhances apoptosis.
On the other hand, the levels of apoptosis were equivalent in CPB21111 andCB21111 pancreata. Thus, apoptosis resulting from Brca2 deficiency in vivo might not bedependent on Trp53 status. In contrast, 4 month CX-4945 old CKB21111 mice displayed 8.6foldhigher levels of in vivo apoptosis than CKB2wt11 and CKB2wtwt mice, suggesting that activated Kras and inactive Brca2 cooperate to promote cell death.Germline mutations within the BRCA2 gene happen to be observed in pancreatic cancer familiesand BRCA2 mutations happen to be detected in unselected adenocarcinomas from the pancreas,suggesting a function for BRCA2 within the development of pancreatic cancer. Here we show, usinga pancreas specific knockout mouse model, that disruption of Brca2 promotes thedevelopment and progression of pancreatic cancer when combined with Trp53 inactivation,but not within the presence of active Trp53 signaling.
Based on our findings we suggest a model,whereby disruption of Trp53 signaling occurs prior to inactivation of the second Brca2allele. In this model, inactive Trp53 signaling allows pancreatic cells to evade the growthinhibitory or cell death14 effects caused by the substantial numerical and structural instabilitythat develops within the absence of functional Brca2 protein. This really is consistent axitinib withthe presence of TP53 mutations in human PDACs containing BRCA2 mutations25. Themodel further suggests that loss of the wildtype BRCA2 allele in human carriers of germlineBRCA2 mutations must occur late within the pancreatic PARP tumor development process following theinactivation of TP53 signaling.
axitinib Support for this comes from studies of human PDAC, whichshowed that the loss of heterozygosityof BRCA2 appears to be a late event intumorigenesis9,26.Somewhat surprisingly our studies also showed that inactivation of Brca2 inhibitsdevelopment of PanINs, metaplastic lesions and PDAC within the wellcharacterized pdx1cre;LSLKrasG12D mouse model. This synthetic lethal effect appears to be related withthe increased chromosomal instability caused by Brca2 deficiency with some evidencesuggesting a synergistic effect of Kras activation and Brca2 disruption on apoptosis. Given our data suggesting that the couple of pancreatic tumors arising in CKB21111 micecontained Trp53 mutations, and the recognized presence of BRCA2, TP53 and KrasG12Vmutations within the human Capan1 pancreatic cancer cell line, the suggestion is that disruptionof Trp53 signaling is again necessary to bypass the effects of Brca2 inactivation in cellsexpressing KrasG12D.
Even though we were unable to produce adequate numbers ofCKPB21111 mice to confirm this model, a pancreas specific CKPB2Tr11 modelinvolving a Trp53R270H allele rather than a Trp53 truncating mutation and also a Brca2Tr CX-4945 allelethat truncates Brca2 at amino acid 1492 has lately been described16. These CKPB2Tr11mice develop pancreatic tumors at high frequency, which in component supports the model thatTrp53 disruption is necessary for tumor formation in Brca2 deficient pancreata, both in thepresence and absence of activated Kras. On the other hand, within the exact same report it was suggested thatCKB2Tr11 mice developed pancreatic cancer within the presence of wildtype Trp53, anobservation that would appear to be contrary to our proposed model.
Careful examination ofthe presented PDACfree KaplanMeier survival estimates suggests that only a smallnumberproportion of CKB2Tr11 mice developed pancreatic tumors16, fully consistent withthe 13tumor incidence at 500 days in our CKB21111 mice. Must thetumors axitinib arising within the CKB2Tr11 mice contain Trp53 mutations or exhibit altered Trp53signaling, similarly to the four tumors from our CKB21111 mice, then the results wouldfurther assistance the proposed model. Since the Trp53 status of the tumors was not reported,additional studies of pancreatic tumors arising in these mice are required. In addition,no matter if aberrations in other regulators of apoptosis and cell cycle can rescue the effects ofBrca2 deficiency remains to be determined. Taken with each other, our final results point to criticaltemporal regulation of the second BRCA2hitand the significance of the interplay betweenBRCA2 and TP53 for development of PDAC.The assortment of diverse tumor varieties observed within the CPB21111 mice suggests a highdegree of plasticity among cells of the pancreas.