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Supplementary Tables 1-2, Figures 1-8 from PTEN Is a Major Tumor Suppressor in Pancreatic Ductal Adenocarcinoma and Regulates an NF-κB–Cytokine Network

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Glioblastomas are lethal brain tumors that are treated with conventional radiation (X-rays and gamma rays) or particle radiation (protons and carbon ions). Paradoxically, radiation is also a risk factor for GBM development, raising the possibility that radiotherapy of brain tumors could promote tumor recurrence or trigger secondary gliomas. In this study, we determined whether tumor suppressor losses commonly displayed by patients with GBM confer susceptibility to radiation-induced glioma. Mice with Nestin-Cre-driven deletions of Trp53 and Pten alleles were intracranially irradiated with X-rays or charged particles of increasing atomic number and linear energy transfer (LET). Mice with loss of one allele each of Trp53 and Pten did not develop spontaneous gliomas, but were highly susceptible to radiation-induced gliomagenesis. Tumor development frequency after exposure to high-LET particle radiation was significantly higher compared with X-rays, in accordance with the irreparability of DNA double-strand breaks (DSB) induced by high-LET radiation. All resultant gliomas, regardless of radiation quality, presented histopathologic features of grade IV lesions and harbored populations of cancer stem-like cells with tumor-propagating properties. Furthermore, all tumors displayed concomitant loss of heterozygosity of Trp53 and Pten along with frequent amplification of the Met receptor tyrosine kinase, which conferred a stem cell phenotype to tumor cells. Our results demonstrate that radiation-induced DSBs cooperate with preexisting tumor suppressor losses to generate high-grade gliomas. Moreover, our mouse model can be used for studies on radiation-induced development of GBM and therapeutic strategies.Significance:This study uncovers mechanisms by which ionizing radiation, especially particle radiation, promote GBM development or recurrence.

Glioblastomas (GBM) are routinely treated with ionizing radiation (IR) but inevitably recur and develop therapy resistance. During treatment, the tissue surrounding tumors is also irradiated. IR potently induces senescence, and senescent stromal cells can promote the growth of neighboring tumor cells by secreting factors that create a senescence-associated secretory phenotype (SASP). Here, we carried out transcriptomic and tumorigenicity analyses in irradiated mouse brains to elucidate how radiotherapy-induced senescence of non-neoplastic brain cells promotes tumor growth. Following cranial irradiation, widespread senescence in the brain occurred, with the astrocytic population being particularly susceptible. Irradiated brains showed an altered transcriptomic profile characterized by upregulation of CDKN1A (p21), a key enforcer of senescence, and several SASP factors, including HGF, the ligand of the receptor tyrosine kinase (RTK) Met. Preirradiation of mouse brains increased Met-driven growth and invasiveness of orthotopically implanted glioma cells. Importantly, irradiated p21−/− mouse brains did not exhibit senescence and consequently failed to promote tumor growth. Senescent astrocytes secreted HGF to activate Met in glioma cells and to promote their migration and invasion in vitro, which could be blocked by HGF-neutralizing antibodies or the Met inhibitor crizotinib. Crizotinib also slowed the growth of glioma cells implanted in preirradiated brains. Treatment with the senolytic drug ABT-263 (navitoclax) selectively killed senescent astrocytes in vivo, significantly attenuating growth of glioma cells implanted in preirradiated brains. These results indicate that SASP factors in the irradiated tumor microenvironment drive GBM growth via RTK activation, underscoring the potential utility of adjuvant senolytic therapy for preventing GBM recurrence after radiotherapy.Significance:This study uncovers mechanisms by which radiotherapy can promote GBM recurrence by inducing senescence in non-neoplastic brain cells, suggesting that senolytic therapy can blunt recurrent GBM growth and aggressiveness.

Figure S1: Cre-mediated excision of floxed alleles and induction of double strand breaks in murine brains. Figure S2: DNA damage in primary astrocytes and murine brains induced by different radiation types. Figure S3: Histopathology and cell lineage markers in radiation-induced gliomas (RIG). Figure S4: Sox2 expression in RIG-derived cell lines and tumor growth kinetics. Figure S5: Loss of p53 and Pten in RIG-derived cell lines. Figure S6: Non-Met amplified RIG. Table S1: List of PCR and RT-PCR primers. Table S2: RIG-derived lines. Table S3: Subcutaneous and orthotopic tumors generated from RIG-derived cell lines. Table S4: A panel of 33 RIGs used for immunohistochemical analysis. Table S5. List of GISTIC hits.

Made available in DSpace on 2022-04-28T19:47:50Z (GMT). No. of bitstreams: 0 Previous issue date: 2021-12-01 Glioblastomas (GBM) are routinely treated with ionizing radiation (IR) but inevitably recur and develop therapy resistance. During treatment, the tissue surrounding tumors is also irradiated. IR potently induces senescence, and senescent stromal cells can promote the growth of neighboring tumor cells by secreting factors that create a senescence-associated secretory phenotype (SASP). Here, we carried out transcriptomic and tumorigenicity analyses in irradiated mouse brains to elucidate how radiotherapy-induced senescence of non-neoplastic brain cells promotes tumor growth. Following cranial irradiation, widespread senescence in the brain occurred, with the astrocytic population being particularly susceptible. Irradiated brains showed an altered transcriptomic profile characterized by upregulation of CDKN1A (p21), a key enforcer of senescence, and several SASP factors, including HGF, the ligand of the receptor tyrosine kinase (RTK) Met. Preirradiation of mouse brains increased Met-driven growth and invasiveness of orthotopically implanted glioma cells. Importantly, irradiated p21_/_ mouse brains did not exhibit senescence and consequently failed to promote tumor growth. Senescent astrocytes secreted HGF to activate Met in glioma cells and to promote their migration and invasion in vitro, which could be blocked by HGF-neutralizing antibodies or the Met inhibitor crizotinib. Crizotinib also slowed the growth of glioma cells implanted in preirradiated brains. Treatment with the senolytic drug ABT-263 (navitoclax) selectively killed senescent astrocytes in vivo, significantly attenuating growth of glioma cells implanted in preirradiated brains. These results indicate that SASP factors in the irradiated tumor microenvironment drive GBM growth via RTK activation, underscoring the potential utility of adjuvant senolytic therapy for preventing GBMrecurrence after radiotherapy. Significance: This study uncovers mechanisms by which radiotherapy can promote GBM recurrence by inducing senescence in non-neoplastic brain cells, suggesting that senolytic therapy can blunt recurrent GBM growth and aggressiveness. _2021 American Association for Cancer Research. Department of Radiation Oncology University of Texas Southwestern Medical Center Department of Neurosurgery University of Texas Health School of Pharmaceutical Sciences S~ao Paulo State University (UNESP) Eugene McDermott Center for Human Growth and Development Department of Biochemistry and Structural Biology University of Texas Health Department of Medicine University of Texas Health Department of Neurologic Surgery Mayo Clinic Department of Neurology University of Texas Southwestern Medical Center Veterans Affairs North Texas Health Care System School of Pharmaceutical Sciences S~ao Paulo State University (UNESP)

Endothelial–to–mesenchymal transition (EndMT) is a cellular transdifferentiation program in which endothelial cells partially lose their endothelial identity and acquire mesenchymal-like features. Renal capillary endothelial cells can undergo EndMT in association with persistent damage of the renal parenchyma. The functional consequence(s) of EndMT in kidney fibrosis remains unexplored. Here, we studied the effect of Twist or Snail deficiency in endothelial cells on EndMT in kidney fibrosis. Conditional deletion of Twist1 (which encodes Twist) or Snai1 (which encodes Snail) in VE-cadherin(+) or Tie1(+) endothelial cells inhibited the emergence of EndMT and improved kidney fibrosis in two different kidney injury/fibrosis mouse models. Suppression of EndMT limited peritubular vascular leakage, reduced tissue hypoxia, and preserved tubular epithelial health and function. Hypoxia, which was exacerbated by EndMT, resulted in increased Myc abundance in tubular epithelial cells, enhanced glycolysis, and suppression of fatty acid oxidation. Pharmacological suppression or epithelial-specific genetic ablation of Myc in tubular epithelial cells ameliorated fibrosis and restored renal parenchymal function and metabolic homeostasis. Together, these findings demonstrate a functional role for EndMT in the response to kidney capillary endothelial injury and highlight the contribution of endothelial-epithelial crosstalk in the development of kidney fibrosis with a potential for therapeutic intervention.

Glioblastomas (GBM) are treated with high doses of ionizing radiation (IR) yet these tumors inevitably recur, and the recurrent tumors are highly therapy resistant. During GBM therapy, the surrounding brain tissue is irradiated along with the tumor. IR induces senescence in multiple cell types, and senescent stromal cells are known to promote the growth of neighboring tumor cells by secreting cytokines which create a senescence-associated secretory phenotype (SASP). We hypothesize that IR-induced senescence of normal brain cells in the tumor microenvironment is a powerful driver of GBM recurrence. We intra-cranially irradiated C57BL/6J mice, and found evidence of widespread senescence, with the astrocytic population being highly susceptible. Genomic analyses of irradiated brains revealed an altered transcriptomic profile which included upregulation of CDKN1A (p21), a key enforcer of senescence, and increased expression of SASP proteins including HGF, the ligand for the RTK Met. We orthotopically implanted mock-irradiated or irradiated mice with a limiting number of syngeneic glioma cells. Pre-irradiation of mouse brains resulted in a striking increase in tumor growth and invasion driven by Met activation in the tumor cells. Importantly, irradiated p21-/- mouse brains did not exhibit SASP and failed to promote tumor growth. Irradiated primary astrocytes underwent senescence in vitro and promoted the migration of glioma cells, and this could be attenuated with HGF-neutralizing antibodies or by the Met inhibitor Crizotinib. These findings indicate that SASP factors (like HGF) in the irradiated brain microenvironment could drive GBM recurrence after radiotherapy via the activation of RTKs (like MET) in the tumor cells. Significantly, we found that senolytic drugs can selectively kill senescent astrocytes both in vitro and in vivo resulting in attenuated growth of glioma cells. These results are of great translational significance as they indicate that adjuvant therapy with senolytic drugs might attenuate GBM recurrence after radiotherapy.

p53 is often mutated or lost in cancer; here inactivation of ΔNp63 and ΔNp73 in the absence of p53 is shown to result in metabolic reprogramming and tumour regression via activation of IAPP (islet amyloid polypeptide or amylin), and IAPP-based anti-diabetes therapeutic strategies show potential for the treatment of p53-deficient and mutant tumours. The tumour suppressor p53 is often mutated or lost in cancer. There is evidence from mouse models that reactivation of p53 activity in tumours can result in regression, but direct reactivation of normal p53 activity has not developed into an effective strategy for treating human cancer. In this paper Elsa Flores and colleagues show in mice that inactivation of the p53 family proteins p63 and p73, in the absence of p53, results in metabolic reprogramming and tumour regression through the activation of IAPP (islet amyloid polypeptide, also known as amylin). The anti-diabetic drug pramlintide, an amylin analogue, caused tumour regression in mice with p53-deficient thymic lymphomas, suggesting a novel strategy that might be used to target p53-deficient cancers. TP53 is commonly altered in human cancer, and Tp53 reactivation suppresses tumours in vivo in mice1,2 (TP53 and Tp53 are also known as p53). This strategy has proven difficult to implement therapeutically, and here we examine an alternative strategy by manipulating the p53 family members, Tp63 and Tp73 (also known as p63 and p73, respectively). The acidic transactivation-domain-bearing (TA) isoforms of p63 and p73 structurally and functionally resemble p53, whereas the ΔN isoforms (lacking the acidic transactivation domain) of p63 and p73 are frequently overexpressed in cancer and act primarily in a dominant-negative fashion against p53, TAp63 and TAp73 to inhibit their tumour-suppressive functions3,4,5,6,7,8. The p53 family interacts extensively in cellular processes that promote tumour suppression, such as apoptosis and autophagy9,10,11,12,13,14, thus a clear understanding of this interplay in cancer is needed to treat tumours with alterations in the p53 pathway. Here we show that deletion of the ΔN isoforms of p63 or p73 leads to metabolic reprogramming and regression of p53-deficient tumours through upregulation of IAPP, the gene that encodes amylin, a 37-amino-acid peptide co-secreted with insulin by the β cells of the pancreas. We found that IAPP is causally involved in this tumour regression and that amylin functions through the calcitonin receptor (CalcR) and receptor activity modifying protein 3 (RAMP3) to inhibit glycolysis and induce reactive oxygen species and apoptosis. Pramlintide, a synthetic analogue of amylin that is currently used to treat type 1 and type 2 diabetes, caused rapid tumour regression in p53-deficient thymic lymphomas, representing a novel strategy to target p53-deficient cancers.

Activating mutations in KRAS are among the most frequent events in diverse human carcinomas and are particularly prominent in human pancreatic ductal adenocarcinoma (PDAC). An inducible Kras(G12D)-driven mouse model of PDAC has established a critical role for sustained Kras(G12D) expression in tumor maintenance, providing a model to determine the potential for and the underlying mechanisms of Kras(G12D)-independent PDAC recurrence. Here, we show that some tumors undergo spontaneous relapse and are devoid of Kras(G12D) expression and downstream canonical MAPK signaling and instead acquire amplification and overexpression of the transcriptional coactivator Yap1. Functional studies established the role of Yap1 and the transcriptional factor Tead2 in driving Kras(G12D)-independent tumor maintenance. The Yap1/Tead2 complex acts cooperatively with E2F transcription factors to activate a cell cycle and DNA replication program. Our studies, along with corroborating evidence from human PDAC models, portend a novel mechanism of escape from oncogenic Kras addiction in PDAC.

Initiation of pancreatic ductal adenocarcinoma (PDAC) is driven by oncogenic KRAS mutation, and disease progression is associated with frequent loss of tumor suppressors. In this study, human PDAC genome analyses revealed frequent deletion of the PTEN gene as well as loss of expression in primary tumor specimens. A potential role for PTEN as a haploinsufficient tumor suppressor is further supported by mouse genetic studies. The mouse PDAC driven by oncogenic Kras mutation and Pten deficiency also sustains spontaneous extinction of Ink4a expression and shows prometastatic capacity. Unbiased transcriptomic analyses established that combined oncogenic Kras and Pten loss promotes marked NF-κB activation and its cytokine network, with accompanying robust stromal activation and immune cell infiltration with known tumor-promoting properties. Thus, PTEN/phosphoinositide 3-kinase (PI3K) pathway alteration is a common event in PDAC development and functions in part to strongly activate the NF-κB network, which may serve to shape the PDAC tumor microenvironment. Significance: Detailed molecular genetics studies established that PTEN operates as a haploinsufficient tumor suppressor to promote metastatic PDAC development. The strong activation of the NF-κB–cytokine program in Pten-deficient tumors provides additional avenues for targeted therapies in tumors with altered PI3K regulation. Cancer Discovery; 1(2); 158–69. ©2011 AACR. Read the Commentary on this article by Chiao and Ling, p. 103 This article is highlighted in the In This Issue feature, p. 91

The capacity to fine-tune cellular bioenergetics with the demands of stem-cell maintenance and regeneration is central to normal development and ageing, and to organismal survival during periods of acute stress. How energy metabolism and stem-cell homeostatic processes are coordinated is not well understood. Lkb1 acts as an evolutionarily conserved regulator of cellular energy metabolism in eukaryotic cells and functions as the major upstream kinase to phosphorylate AMP-activated protein kinase (AMPK) and 12 other AMPK-related kinases. Whether Lkb1 regulates stem-cell maintenance remains unknown. Here we show that Lkb1 has an essential role in haematopoietic stem cell (HSC) homeostasis. We demonstrate that ablation of Lkb1 in adult mice results in severe pancytopenia and subsequent lethality. Loss of Lkb1 leads to impaired survival and escape from quiescence of HSCs, resulting in exhaustion of the HSC pool and a marked reduction of HSC repopulating potential in vivo. Lkb1 deletion has an impact on cell proliferation in HSCs, but not on more committed compartments, pointing to context-specific functions for Lkb1 in haematopoiesis. The adverse impact of Lkb1 deletion on haematopoiesis was predominantly cell-autonomous and mTOR complex 1 (mTORC1)-independent, and involves multiple mechanisms converging on mitochondrial apoptosis and possibly downregulation of PGC-1 coactivators and their transcriptional network, which have critical roles in mitochondrial biogenesis and function. Thus, Lkb1 serves as an essential regulator of HSCs and haematopoiesis, and more generally, points to the critical importance of coupling energy metabolism and stem-cell homeostasis.

Tumor maintenance relies on continued activity of driver oncogenes, although their rate-limiting role is highly context-dependent. Oncogenic Kras mutation is the signature event in pancreatic ductal adenocarcinoma (PDAC), serving a critical role in tumor initiation. Here, an inducible KrasG12D-driven PDAC mouse model establishes that advanced PDAC remain strictly dependent on KrasG12D expression. Transcriptome and metabolomic analysis indicate that KrasG12D serves a vital role in controlling tumor metabolism through stimulation of glucose uptake and channeling of glucose intermediates into the hexosamine biosynthesis and pentose phosphate pathways (PPP). These studies also reveal that oncogenic Kras promotes ribose biogenesis. Unlike canonical models, we demonstrate that KrasG12D drives glycolysis intermediates into the non-oxidative PPP, thereby decoupling ribose biogenesis from NADP/NADPH-mediated redox control. Together, this work provides in vivo mechanistic insights into how oncogenic Kras promotes metabolic reprogramming in native tumors and illuminates potential metabolic targets that can be exploited for therapeutic benefit in PDAC. Citation Format: Haoqiang Ying, Hailei Zhang, Jonathan L. Coloff, Haiyan Yan, Wei Wang, Shujuan Chen, Andrea Viale, Hongwu Zheng, Ji-hye Paik, Carol Lim, Alexander R. Guimaraes, Alec C. Kimmelman, Eric S. Martin, Jeffery Chang, Aram Hezel, Samuel R. Perry, Jian Hu, Boyi Gan, Yonghong Xiao, John M. Asara, Ralph Weissleder, Y. Alan Wang, Costas A. Lyssiotis, Lynda Chin, Lewis C. Cantley, Ronald A. DePinho, Sujun Hua, Gerald C. Chu, Eliot Fletcher-Sananikone, Jason W. Locasale, Jaekyoung Son. Oncogenic Kras maintains pancreatic tumors through regulation of anabolic glucose metabolism. [abstract]. In: Proceedings of the AACR Special Conference on Pancreatic Cancer: Progress and Challenges; Jun 18-21, 2012; Lake Tahoe, NV. Philadelphia (PA): AACR; Cancer Res 2012;72(12 Suppl):Abstract nr A101.

Tumor maintenance relies on continued activity of driver oncogenes, although their rate-limiting role is highly context dependent. Oncogenic Kras mutation is the signature event in pancreatic ductal adenocarcinoma (PDAC), serving a critical role in tumor initiation. Here, an inducible Kras(G12D)-driven PDAC mouse model establishes that advanced PDAC remains strictly dependent on Kras(G12D) expression. Transcriptome and metabolomic analyses indicate that Kras(G12D) serves a vital role in controlling tumor metabolism through stimulation of glucose uptake and channeling of glucose intermediates into the hexosamine biosynthesis and pentose phosphate pathways (PPP). These studies also reveal that oncogenic Kras promotes ribose biogenesis. Unlike canonical models, we demonstrate that Kras(G12D) drives glycolysis intermediates into the nonoxidative PPP, thereby decoupling ribose biogenesis from NADP/NADPH-mediated redox control. Together, this work provides in vivo mechanistic insights into how oncogenic Kras promotes metabolic reprogramming in native tumors and illuminates potential metabolic targets that can be exploited for therapeutic benefit in PDAC.

SummarymTORC1 is a validated therapeutic target for renal cell carcinoma (RCC). Here, analysis of Tsc1-deficient (mTORC1 hyperactivation) mice uncovered a FoxO-dependent negative feedback circuit constraining mTORC1-mediated renal tumorigenesis. We document robust FoxO activation in Tsc1-deficient benign polycystic kidneys and FoxO extinction on progression to murine renal tumors; murine renal tumor progression on genetic deletion of both Tsc1 and FoxOs; and downregulated FoxO expression in most human renal clear cell and papillary carcinomas, yet continued expression in less aggressive RCCs and benign renal tumor subtypes. Mechanistically, integrated analyses revealed that FoxO-mediated block operates via suppression of Myc through upregulation of the Myc antagonists, Mxi1-SRα and mir-145, establishing a FoxO-Mxi1-SRα/mir-145 axis as a major progression block in renal tumor development.

Nature 488, 337–342 (2012); doi:10.1038/nature11331 In this Article, during the preparation of Figures 2d and 3a, we processed digital western blot scans to remove duplicate or otherwise irrelevant lanes from single-blot images. Although all excisions/mergers originated from the same gel, these figure constructions should have been explicitly pointed out.

Activating mutations in KRAS are among the most frequent events in diverse human carcinomas and particularly prominent in human pancreatic ductal adenocarcinoma (PDAC). An inducible KrasG12D-driven mouse model of PDAC has established a critical role for sustained KrasG12D expression in tumor maintenance, providing a model to determine the potential for, and underlying mechanisms of, KrasG12D–independent PDAC recurrence. Here we show that majority tumors will undergo spontaneous regrowth following Kras oncogene extinction and, importantly, a subset of relapsed tumors remained devoid of KrasG12D expression and canonical MAPK signaling and acquired amplification and over-expression of Hippo effector, the Yap1 transcriptional co-activator. Functional studies established Yap1 and the Tead2 transcriptional factor in driving KrasG12D–independent tumor maintenance. The Yap1/Tead2 complex acts cooperatively with E2F transcription factors to promote a cell cycle and DNA replication program and a quasimesenchymal phenotype with increased metastatic potential. Our studies, along with corroborating evidence from human PDAC models, portend a novel mechanism of escape from oncogenic Kras addiction in PDAC. This abstract is also presented as Poster B21. Citation Format: Avnish Kapoor, Wantong Yao, Haoqiang Ying, Sujun Hua, Alison Liewen, Qiuyun Wang, Yi Zhong, Chang-Jiun Wu, Anguraj Sadanandam, Baoli Hu, Qing Chang, Gerald Chu, Ramsey Al-Khalil, Shan Jiang, Hongai Xia, Eliot Fletcher-Sananikone, Carol Lim, Gillian Horwitz, Andrea Viale, Piergiorgio Pettazzoni, Nora Sanchez, Huamin Wang, Alexei Protopopov, Jianhua Zhang, Timothy Heffernan, Randy Johnson, Lynda Chin, Alan Wang, Giulio Draetta, Ronald DePinho. Yap1 activation enables bypass of oncogenic Kras addiction in pancreatic cancer. [abstract]. In: Proceedings of the AACR Special Conference on RAS Oncogenes: From Biology to Therapy; Feb 24-27, 2014; Lake Buena Vista, FL. Philadelphia (PA): AACR; Mol Cancer Res 2014;12(12 Suppl):Abstract nr PR01. doi: 10.1158/1557-3125.RASONC14-PR01

p53 tumor suppressor undergoes mutational loss in majority of cancers contributing to tumor formation. Therapeutic strategies are aimed towards p53 overexpression in tumors or to identify targets that compensate for p53-functional loss. p63 & p73, share structural similarities to p53, making them excellent candidates for therapeutic compensation of p53. Unlike p53, p63 and p73 do not undergo mutational loss and their role in tumorigenesis is being delineated. p63 and p73 have two major isoforms, the transactivation (TA), with activities similar to p53 and the delta (Δ)N- isoform with oncogenic functions. Inhibition of TAp63 and TAp73 is observed in cancers as a consequence of overexpression of ΔN isoforms of p63 and p73. In disparity, recent studies report, tumor suppressive properties of ΔNp63 and ΔNp73 in activating genes involved in DNA repair and apoptosis. To define the functional roles of ΔNp63 and ΔNp73 in cancer, mouse models targeting the ΔN isoforms were generated. We observed that, ΔNp63+/- and ΔNp73−/− mice on a p53−/− background had lower thymic lymphoma incidence compared to the p53−/− mice. I found TAp63 and TAp73 up regulated in the double mutant mice that correspond with an increase in p53-downstream apoptotic (PUMA, Noxa, BAX) and cell cycle targets (p21, p16, PML). This suggests that ablation of ΔN isoforms mediate TAp63 and TAp73 up regulation inducing apoptosis or cell cycle arrest by activation of p53-downstream targets. To further demonstrate this, I ablated ΔNp63 and ΔNp73 in vivo in p53−/- mice thymic lymphoma by administering adenoviral-CRE specifically to the thymus. The CRE-treated mice had a significant thymic lymphoma regression within 3 weeks as imaged by MRI in comparison to the mock-treated mouse cohorts. Additionally, RNA-Seq analysis from CRE-treated versus untreated mice, has identified novel metabolic genes with apoptotic or cell-cycle functions. We further report, ΔNp63 and ΔNp73 to bind to promoter site of TAp63 and TAp73 by chromatin immunoprecipitation (ChIP). This supports the notion that ablation of ΔN isoforms of p63 and p73 restores the function of TAp63 and TAp73 thus compensating for p53-tumor suppressive function in vivo. To test, if ablation of ΔN isoforms reduces tumorigenesis in human cancers, ΔNp63 and ΔNp73 were knocked down in human cancer cell lines were p53 expression was ablated or mutated. TAp63 and TAp73 were upregulated in ΔNp63/ΔNp73 knock down human cancer cell lines. However, induction of apoptosis or cell-cycle arrest was observed in p53-deleted cancer cell lines in comparison to the p53-mutated cell lines. This highlights the co-repressive effect of mutant p53, preventing activation of TAp63/TAp73 downstream targets. Current work is aimed towards overcoming mutant p53 effect in these cancer cell lines. Thus, targeting the ΔNp63/ΔNp73 compensates for p53-functional loss mediating tumor suppression. Citation Format: Avinashnarayan Venkatanarayan, Deepavali Chakravarti, Xiaohua Su, Santosh Sandur, Lingzhi Liu, Eliot Fletcher Sananikone, Payal Raulji, Cristian Coarfa, William Norton, Preethi Gunaratne, Elsa Renee Flores. Deletion of ΔNp63 and ΔNp73 in p53 deficient mice results in TAp63 and TAp73 compensation of p53 tumor suppression in vivo. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 2331. doi:10.1158/1538-7445.AM2013-2331