Epithelial TGFβ engages growth-factor signalling to circumvent apoptosis and drive intestinal tumourigenesis with aggressive features

The pro-tumourigenic role of epithelial TGFβ signalling in colorectal cancer (CRC) is controversial. Here, we identify a cohort of born to be bad early-stage (T1) colorectal tumours, with aggressive features and a propensity to disseminate early, that are characterised by high epithelial cell-intrinsic TGFβ signalling. In the presence of concurrent Apc and Kras mutations, activation of epithelial TGFβ signalling rampantly accelerates tumourigenesis and share transcriptional signatures with those of the born to be bad T1 human tumours and predicts recurrence in stage II CRC. Mechanistically, epithelial TGFβ signalling induces a growth-promoting EGFR-signalling module that synergises with mutant APC and KRAS to drive MAPK signalling that re-sensitise tumour cells to MEK and/or EGFR inhibitors. Together, we identify epithelial TGFβ signalling both as a determinant of early dissemination and a potential therapeutic vulnerability of CRC's with born to be bad traits.

Aberrant Expression and Subcellular Localization of ECT2 Drives Colorectal Cancer Progression and Growth

ECT2 is an activator of RHO GTPases that is essential for cytokinesis. In addition, ECT2 was identified as an oncoprotein when expressed ectopically in NIH/3T3 fibroblasts. However, oncogenic activation of ECT2 resulted from N-terminal truncation, and such truncated ECT2 proteins have not been found in patients with cancer. In this study, we observed elevated expression of full-length ECT2 protein in preneoplastic colon adenomas, driven by increased ECT2 mRNA abundance and associated with APC tumor-suppressor loss. Elevated ECT2 levels were detected in the cytoplasm and nucleus of colorectal cancer tissue, suggesting cytoplasmic mislocalization as one mechanism of early oncogenic ECT2 activation. Importantly, elevated nuclear ECT2 correlated with poorly differentiated tumors, and a low cytoplasmic:nuclear ratio of ECT2 protein correlated with poor patient survival, suggesting that nuclear and cytoplasmic ECT2 play distinct roles in colorectal cancer. Depletion of ECT2 reduced anchorage-independent cancer cell growth and invasion independent of its function in cytokinesis, and loss of Ect2 extended survival in a Kras G12D Apc-null colon cancer mouse model. Expression of ECT2 variants with impaired nuclear localization or guanine nucleotide exchange catalytic activity failed to restore cancer cell growth or invasion, indicating that active, nuclear ECT2 is required to support tumor progression. Nuclear ECT2 promoted ribosomal DNA transcription and ribosome biogenesis in colorectal cancer. These results support a driver role for both cytoplasmic and nuclear ECT2 overexpression in colorectal cancer and emphasize the critical role of precise subcellular localization in dictating ECT2 function in neoplastic cells. SIGNIFICANCE: ECT2 overexpression and mislocalization support its role as a driver in colon cancer that is independent from its function in normal cell cytokinesis.

Oncogenic BRAF, unrestrained by TGFβ-receptor signalling, drives right-sided colonic tumorigenesis

Right-sided (proximal) colorectal cancer (CRC) has a poor prognosis and a distinct mutational profile, characterized by oncogenic BRAF mutations and aberrations in mismatch repair and TGFβ signalling. Here, we describe a mouse model of right-sided colon cancer driven by oncogenic BRAF and loss of epithelial TGFβ-receptor signalling. The proximal colonic tumours that develop in this model exhibit a foetal-like progenitor phenotype (Ly6a/Sca1⁺) and, importantly, lack expression of Lgr5 and its associated intestinal stem cell signature. These features are recapitulated in human BRAF-mutant, right-sided CRCs and represent fundamental differences between left- and right-sided disease. Microbial-driven inflammation supports the initiation and progression of these tumours with foetal-like characteristics, consistent with their predilection for the microbe-rich right colon and their antibiotic sensitivity. While MAPK-pathway activating mutations drive this foetal-like signature via ERK-dependent activation of the transcriptional coactivator YAP, the same foetal-like transcriptional programs are also initiated by inflammation in a MAPK-independent manner. Importantly, in both contexts, epithelial TGFβ-receptor signalling is instrumental in suppressing the tumorigenic potential of these foetal-like progenitor cells.

Oncogenic BRAF, unrestrained by TGFβ-receptor signalling, drives right-sided colonic tumorigenesis

Right-sided (proximal) colorectal cancer (CRC) has a poor prognosis and a distinct mutational profile, characterized by oncogenic BRAF mutations and aberrations in mismatch repair and TGFβ signalling. Here, we describe a mouse model of right-sided colon cancer driven by oncogenic BRAF and loss of epithelial TGFβ-receptor signalling. The proximal colonic tumours that develop in this model exhibit a foetal-like progenitor phenotype (Ly6a/Sca1+) and, importantly, lack expression of Lgr5 and its associated intestinal stem cell signature. These features are recapitulated in human BRAF-mutant, right-sided CRCs and represent fundamental differences between left- and right-sided disease. Microbial-driven inflammation supports the initiation and progression of these tumours with foetal-like characteristics, consistent with their predilection for the microbe-rich right colon and their antibiotic sensitivity. While MAPK-pathway activating mutations drive this foetal-like signature via ERK-dependent activation of the transcriptional coactivator YAP, the same foetal-like transcriptional programs are also initiated by inflammation in a MAPK-independent manner. Importantly, in both contexts, epithelial TGFβ-receptor signalling is instrumental in suppressing the tumorigenic potential of these foetal-like progenitor cells.

A RAC-GEF network critical for early intestinal tumourigenesis

RAC1 activity is critical for intestinal homeostasis, and is required for hyperproliferation driven by loss of the tumour suppressor gene Apc in the murine intestine. To avoid the impact of direct targeting upon homeostasis, we reasoned that indirect targeting of RAC1 via RAC-GEFs might be effective. Transcriptional profiling of Apc deficient intestinal tissue identified Vav3 and Tiam1 as key targets. Deletion of these indicated that while TIAM1 deficiency could suppress Apc-driven hyperproliferation, it had no impact upon tumourigenesis, while VAV3 deficiency had no effect. Intriguingly, deletion of either gene resulted in upregulation of Vav2, with subsequent targeting of all three (Vav2-/- Vav3-/- Tiam1-/-), profoundly suppressing hyperproliferation, tumourigenesis and RAC1 activity, without impacting normal homeostasis. Critically, the observed RAC-GEF dependency was negated by oncogenic KRAS mutation. Together, these data demonstrate that while targeting RAC-GEF molecules may have therapeutic impact at early stages, this benefit may be lost in late stage disease.

A novel mouse model of testicular granulosa cell tumors

STUDY QUESTION

What is the role of dysregulated transforming growth factor beta (TGFB) signaling in the development of sex cord-stromal tumors in the testis?

SUMMARY ANSWER

Overactivation of TGFB signaling results in the development of testicular tumors resembling granulosa cell tumors (GrCTs).

WHAT IS KNOWN ALREADY

In an earlier study, we demonstrated that constitutively active TGFB receptor 1 (TGFBR1) in ovarian somatic cells promotes the development of ovarian GrCTs. However, the consequence of dysregulation of TGFB signaling in the pathobiology of the testis, remains poorly defined.

STUDY DESIGN, SIZE, DURATION

To identify the impact of dysregulation of TGFB signaling on the testis, we generated mice with constitutive activation of TGFBR1 using anti-Mullerian hormone receptor type 2 (Amhr2)-Cre recombinase. The effect of constitutively active TGFBR1 on testis development and the timeline of testicular tumor formation were examined. We further investigated the molecular features of testicular tumors and determined the expression of beta-catenin (CTNNB1) known to be involved in testicular GrCT development.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Male mice with constitutive activation of TGFBR1 were examined at various developmental stages (i.e. from 1 week up to 6 months) along with controls. Testis samples were collected and processed for histological and molecular analyses, including haematoxylin and eosin (H and E) staining, real-time PCR, immunohistochemistry, immunofluorescence and western blotting. Immunostaining/immunoblotting and real-time PCR experiments were performed using at least three animals per genotype. Data are presented as mean ± SEM. Statistical significance was determined using unpaired two-tail t-test and reported when P value is <0.05.

MAIN RESULTS AND THE ROLE OF CHANCE

Mice harboring constitutively active TGFBR1 in the testes developed tumors resembling testicular GrCTs, a rare type of tumors in the testis. The formation of testicular tumors led to altered cell proliferation, loss of germ cells and defective spermatogenesis. Immunohistochemically, these tumors were positive for inhibin alpha (INHA), forkhead box O1 (FOXO1), and more importantly, forkhead box L2 (FOXL2), a protein specifically expressed in the ovary and required for normal granulosa cell differentiation and function. Consistent with the immunohistochemical findings, FOXL2 proteins were only detectable in testes of TGFBR1-CAAcre mice but not those of controls by western blotting, suggesting potential alteration of Sertoli cell fate. To explore mechanisms underlying the tumor-promoting effect of TGFBR1 overactivation, we examined the expression of CTNNB1. The results revealed increased expression of CTNNB1 in testicular tumors in TGFBR1-CAAcre mice. Collectively, this study uncovered tumorigenic function of enhanced TGFB signaling in the testis.

LARGE-SCALE DATA

N/A.

LIMITATIONS, REASONS FOR CAUTION

This study was performed using mice, and the direct relevance of the experimental paradigm and findings to human testicular GrCTs awaits further investigation. Of note, constitutive activation of TGFBR1 was employed to enhance TGFB/SMAD signaling activity and may not be interpreted as the genetic cause of the disease.

WIDER IMPLICATIONS OF THE FINDINGS

This mouse model may prove to be a useful addition to the mouse genetics toolkit for GrCT research. Our finding that dysregulation of TGFB signaling results in the development of testicular GrCTs supports a common origin between Sertoli cells and granulosa cells, and highlights the paramount importance of balanced TGFB signaling in reproduction and development.

STUDY FUNDING/COMPETING INTEREST(S)

This research was supported by the National Institutes of Health grant R03HD082416 from the Eunice Kennedy Shriver National Institute of Child Health & Human Development and the New Faculty Start-up Funds from Texas A&M University awarded to Q.L. The authors declare no competing interest.

TGFβ inhibition restores a regenerative response in acute liver injury by suppressing paracrine senescence

Liver injury results in rapid regeneration through hepatocyte proliferation and hypertrophy. However, after acute severe injury, such as acetaminophen poisoning, effective regeneration may fail. We investigated how senescence may underlie this regenerative failure. In human acute liver disease, and murine models, p21-dependent hepatocellular senescence was proportionate to disease severity and was associated with impaired regeneration. In an acetaminophen injury mouse model, a transcriptional signature associated with the induction of paracrine senescence was observed within 24 hours and was followed by one of impaired proliferation. In mouse genetic models of hepatocyte injury and senescence, we observed transmission of senescence to local uninjured hepatocytes. Spread of senescence depended on macrophage-derived transforming growth factor-β1 (TGFβ1) ligand. In acetaminophen poisoning, inhibition of TGFβ receptor 1 (TGFβR1) improved mouse survival. TGFβR1 inhibition reduced senescence and enhanced liver regeneration even when delivered beyond the therapeutic window for treating acetaminophen poisoning. This mechanism, in which injury-induced senescence impairs liver regeneration, is an attractive therapeutic target for developing treatments for acute liver failure.

Loss of N-WASP drives early progression in an Apc model of intestinal tumourigenesis

N-WASP (WASL) is a widely expressed cytoskeletal signalling and scaffold protein also implicated in regulation of Wnt signalling and homeostatic maintenance of skin epithelial architecture. N-WASP mediates invasion of cancer cells in vitro and its depletion reduces invasion and metastatic dissemination of breast cancer. Given this role in cancer invasion and universal expression in the gastrointestinal tract, we explored a role for N-WASP in the initiation and progression of colorectal cancer. While deletion of N-wasp is not detectably harmful in the murine intestinal tract, numbers of Paneth cells increased, indicating potential changes in the stem cell niche, and migration up the crypt-villus axis was enhanced. Loss of N-wasp promoted adenoma formation in an adenomatous polyposis coli (Apc) deletion model of intestinal tumourigenesis. Thus, we establish a tumour suppressive role of N-WASP in early intestinal carcinogenesis despite its later pro-invasive role in other cancers. Our study highlights that while the actin cytoskeletal machinery promotes invasion of cancer cells, it also maintains normal epithelial tissue function and thus may have tumour suppressive roles in pre-neoplastic tissues. © 2018 The Authors. The Journal of Pathology published by John Wiley & Sons Ltd on behalf of Pathological Society of Great Britain and Ireland.

Disruption of postnatal folliculogenesis and development of ovarian tumor in a mouse model with aberrant transforming growth factor beta signaling

BACKGROUND

Transforming growth factor beta (TGFB) superfamily signaling is implicated in the development of sex cord-stromal tumors, a category of poorly defined gonadal tumors. The aim of this study was to determine potential effects of dysregulated TGFB signaling in the ovary using Cre recombinase driven by growth differentiation factor 9 (Gdf9) promoter known to be expressed in oocytes.

METHODS

A mouse model containing constitutively active TGFBR1 (TGFBR1^CA) using Gdf9-iCre (termed TGFBR1-CA^G9Cre) was generated. Hematoxylin and eosin (H & E) staining, follicle counting, and immunohistochemistry and immunofluorescence analyses using antibodies directed to Ki67, forkhead box L2 (FOXL2), forkhead box O1 (FOXO1), inhibin alpha (INHA), and SRY (sex determining region Y)-box 9 were performed to determine the characteristics of the TGFBR1-CA^G9Cre ovary. Terminal deoxynucleotidyl transferase (TdT) labeling of 3'-OH ends of DNA fragments, real-time PCR, and western blotting were used to examine apoptosis, select gene expression, and TGFBR1 activation. RNAscope in situ hybridization was used to localize the expression of GLI-Kruppel family member GLI1 (Gli1) in ovarian tumor tissues.

RESULTS

TGFBR1-CA^G9Cre females were sterile. Sustained activation of TGFBR1 led to altered granulosa cell proliferation evidenced by high expression of Ki67. At an early age, these mice demonstrated follicular defects and development of ovarian granulosa cell tumors, which were immunoreactive for granulosa cell markers including FOXL2, FOXO1, and INHA. Further histochemical and molecular analyses provided evidence of overactivation of TGFBR1 in the granulosa cell compartment during ovarian pathogenesis in TGFBR1-CA^G9Cre mice, along with upregulation of Gli1 and Gli2 and downregulation of Tgfbr3 in ovarian tumor tissues.

CONCLUSIONS

These results reinforce the role of constitutively active TGFBR1 in promoting ovarian tumorigenesis in mice. The mouse model created in this study may be further exploited to define the cellular and molecular mechanisms of TGFB/activin downstream signaling in granulosa cell tumor development. Future studies are needed to test whether activation of TGFB/activin signaling contributes to the development of human granulosa cell tumors.

TGFβ pathway limits dedifferentiation following WNT and MAPK pathway activation to suppress intestinal tumourigenesis

Recent studies have suggested increased plasticity of differentiated cells within the intestine to act both as intestinal stem cells (ISCs) and tumour-initiating cells. However, little is known of the processes that regulate this plasticity. Our previous work has shown that activating mutations of Kras or the NF-κB pathway can drive dedifferentiation of intestinal cells lacking Apc. To investigate this process further, we profiled both cells undergoing dedifferentiation in vitro and tumours generated from these cells in vivo by gene expression analysis. Remarkably, no clear differences were observed in the tumours; however, during dedifferentiation in vitro we found a marked upregulation of TGFβ signalling, a pathway commonly mutated in colorectal cancer (CRC). Genetic inactivation of TGFβ type 1 receptor (Tgfbr1/Alk5) enhanced the ability of KrasG12D/+ mutation to drive dedifferentiation and markedly accelerated tumourigenesis. Mechanistically this is associated with a marked activation of MAPK signalling. Tumourigenesis from differentiated compartments is potently inhibited by MEK inhibition. Taken together, we show that tumours arising in differentiated compartments will be exposed to different suppressive signals, for example, TGFβ and blockade of these makes tumourigenesis more efficient from this compartment.

Acinar-to-Ductal Metaplasia Induced by Transforming Growth Factor Beta Facilitates KRASG12D-driven Pancreatic Tumorigenesis

BACKGROUND & AIMS

Transforming growth factor beta (TGFβ) acts either as a tumor suppressor or as an oncogene, depending on the cellular context and time of activation. TGFβ activates the canonical SMAD pathway through its interaction with the serine/threonine kinase type I and II heterotetrameric receptors. Previous studies investigating TGFβ-mediated signaling in the pancreas relied either on loss-of-function approaches or on ligand overexpression, and its effects on acinar cells have so far remained elusive.

METHODS

We developed a transgenic mouse model allowing tamoxifen-inducible and Cre-mediated conditional activation of a constitutively active type I TGFβ receptor (TβRICA) in the pancreatic acinar compartment.

RESULTS

We observed that TβRICA expression induced acinar-to-ductal metaplasia (ADM) reprogramming, eventually facilitating the onset of KRASG12D-induced pre-cancerous pancreatic intraepithelial neoplasia. This phenotype was characterized by the cellular activation of apoptosis and dedifferentiation, two hallmarks of ADM, whereas at the molecular level, we evidenced a modulation in the expression of transcription factors such as Hnf1β, Sox9, and Hes1.

CONCLUSIONS

We demonstrate that TGFβ pathway activation plays a crucial role in pancreatic tumor initiation through its capacity to induce ADM, providing a favorable environment for KRASG12D-dependent carcinogenesis. Such findings are highly relevant for the development of early detection markers and of potentially novel treatments for pancreatic cancer patients.

Modulating the therapeutic response of tumours to dietary serine and glycine starvation

The non-essential amino acids serine and glycine are used in multiple anabolic processes that support cancer cell growth and proliferation (reviewed in ref. 1). While some cancer cells upregulate de novo serine synthesis, many others rely on exogenous serine for optimal growth. Restriction of dietary serine and glycine can reduce tumour growth in xenograft and allograft models. Here we show that this observation translates into more clinically relevant autochthonous tumours in genetically engineered mouse models of intestinal cancer (driven by Apc inactivation) or lymphoma (driven by Myc activation). The increased survival following dietary restriction of serine and glycine in these models was further improved by antagonizing the anti-oxidant response. Disruption of mitochondrial oxidative phosphorylation (using biguanides) led to a complex response that could improve or impede the anti-tumour effect of serine and glycine starvation. Notably, Kras-driven mouse models of pancreatic and intestinal cancers were less responsive to depletion of serine and glycine, reflecting an ability of activated Kras to increase the expression of enzymes that are part of the serine synthesis pathway and thus promote de novo serine synthesis.

Mutational activation of BRAF confers sensitivity to transforming growth factor beta inhibitors in human cancer cells

Recent data implicate elevated transforming growth factor-β (TGFβ) signalling in BRAF inhibitor drug-resistance mechanisms, but the potential for targeting TGFβ signalling in cases of advanced melanoma has not been investigated. We show that mutant BRAFV600E confers an intrinsic dependence on TGFβ/TGFβ receptor 1 (TGFBR1) signalling for clonogenicity of murine melanocytes. Pharmacological inhibition of the TGFBR1 blocked the clonogenicity of human mutant BRAF melanoma cells through SMAD4-independent inhibition of mitosis, and also inhibited metastasis in xenografted zebrafish. When investigating the therapeutic potential of combining inhibitors of mutant BRAF and TGFBR1, we noted that unexpectedly, low-dose PLX-4720 (a vemurafenib analogue) promoted proliferation of drug-naïve melanoma cells. Pharmacological or pharmacogenetic inhibition of TGFBR1 blocked growth promotion and phosphorylation of SRC, which is frequently associated with vemurafenib-resistance mechanisms. Importantly, vemurafenib-resistant patient derived cells retained sensitivity to TGFBR1 inhibition, suggesting that TGFBR1 could be targeted therapeutically to combat the development of vemurafenib drug-resistance.

Inactivation of TGFβ receptors in stem cells drives cutaneous squamous cell carcinoma

Melanoma patients treated with oncogenic BRAF inhibitors can develop cutaneous squamous cell carcinoma (cSCC) within weeks of treatment, driven by paradoxical RAS/RAF/MAPK pathway activation. Here we identify frequent TGFBR1 and TGFBR2 mutations in human vemurafenib-induced skin lesions and in sporadic cSCC. Functional analysis reveals these mutations ablate canonical TGFβ Smad signalling, which is localized to bulge stem cells in both normal human and murine skin. MAPK pathway hyperactivation (through Braf(V600E) or Kras(G12D) knockin) and TGFβ signalling ablation (through Tgfbr1 deletion) in LGR5(+ve) stem cells enables rapid cSCC development in the mouse. Mutation of Tp53 (which is commonly mutated in sporadic cSCC) coupled with Tgfbr1 deletion in LGR5(+ve) cells also results in cSCC development. These findings indicate that LGR5(+ve) stem cells may act as cells of origin for cSCC, and that RAS/RAF/MAPK pathway hyperactivation or Tp53 mutation, coupled with loss of TGFβ signalling, are driving events of skin tumorigenesis.

Constitutively active transforming growth factor β receptor 1 in the mouse ovary promotes tumorigenesis

Despite the well-established tumor suppressive role of TGFβ proteins, depletion of key TGFβ signaling components in the mouse ovary does not induce a growth advantage. To define the role of TGFβ signaling in ovarian tumorigenesis, we created a mouse model expressing a constitutively active TGFβ receptor 1 (TGFBR1) in ovarian somatic cells using conditional gain-of-function approach. Remarkably, these mice developed ovarian sex cord-stromal tumors with complete penetrance, leading to reproductive failure and mortality. The tumors expressed multiple granulosa cell markers and caused elevated serum inhibin and estradiol levels, reminiscent of granulosa cell tumors. Consistent with the tumorigenic effect, overactivation of TGFBR1 altered tumor microenvironment by promoting angiogenesis and enhanced ovarian cell proliferation, accompanied by impaired cell differentiation and dysregulated expression of critical genes in ovarian function. By further exploiting complementary genetic models, we substantiated our finding that constitutively active TGFBR1 is a potent oncogenic switch in mouse granulosa cells. In summary, overactivation of TGFBR1 drives gonadal tumor development. The TGFBR1 constitutively active mouse model phenocopies a number of morphological, hormonal, and molecular features of human granulosa cell tumors and are potentially valuable for preclinical testing of targeted therapies to treat granulosa cell tumors, a class of poorly defined ovarian malignancies.

TIF1γ Suppresses Tumor Progression by Regulating Mitotic Checkpoints and Chromosomal Stability

The transcription accessory factor TIF1γ/TRIM33/RFG7/PTC7/Ectodermin functions as a tumor suppressor that promotes development and cellular differentiation. However, its precise function in cancer has been elusive. In the present study, we report that TIF1γ inactivation causes cells to accumulate chromosomal defects, a hallmark of cancer, due to attenuations in the spindle assembly checkpoint and the post-mitotic checkpoint. TIF1γ deficiency also caused a loss of contact growth inhibition and increased anchorage-independent growth in vitro and in vivo. Clinically, reduced TIF1γ expression in human tumors correlated with an increased rate of genomic rearrangements. Overall, our work indicates that TIF1γ exerts its tumor-suppressive functions in part by promoting chromosomal stability.

Abstract 1506: Frequent loss of function mutations in TGFβR1 and TGFβR2 identify hair follicle bulge stem cells as the cell of origin for cutaneous squamous cell carcinoma

Solid tumors are typically considered to arise from the accumulation of mutations within either stem or differentiated cells and to evolve over several years. However, melanoma patients treated with inhibitors of oncogenic BRAF frequently present with keratoacanthomas and/or cutaneous squamous cell carcinoma (cSCC) within weeks of treatment, possibly driven by paradoxical RAS/RAF MAPK pathway activation. Here, we identify frequent HRAS, TGFβR1 and TGFβR2 mutations in skin lesions from vemurafenib treated patients. Analysis of 98 human sporadic cSCC tumor samples and 21 cSCC cell lines revealed mutation of TGFβ receptors in 42% of samples and activating RAS mutations in 9% of samples. Functional analysis indicates that TGFβ receptor mutations frequently result in loss of canonical signaling. Analysis of normal human skin revealed localised TGFβ signaling in hair follicle bulge stem cells. In murine skin autocrine TGFβ signaling was highly localised to Lgr5+ve stem cells. We modelled hyperactivation of the MAPK pathway (through knockin of BRafV600E or KRASG12D) and the consequences of TGFβ signalling ablation (through the deletion of Tgfβr1) in Lgr5+ve cells. Whist BRaf or KRAS activation alone did not lead to cancer, homozygous deletion of Tgfβr1 enabled rapid cSCC development. Taken together, our results indicate that Lgr5+ve stem cells can act as the cell of origin for cSCC and that hyperactivation of the RAS-RAF-MAPK pathway, coupled with loss of TGFβ signalling, are driving events of skin tumorigenesis.

Citation Format: Patrizia Cammareri, Aidan M. Rose, David F. Vincent, Silvana Libertini, Rachel A. Ridgway, Dimitris Athineos, Philip Coates, Angela McHugh, Celine Pourreyron, Jonas Larsson, Lindsay C. Spender, Gopal Sapkota, Karin Purdie, Charlotte Proby, Catherine A. Harwood, Irene M. Leigh, Hans Clevers, Nicholas Barker, Stefan Karlsson, Catrin Pritchard, Richard Marais, Andrew P. South, Owen J. Sansom, Gareth J. Inman. Frequent loss of function mutations in TGFβR1 and TGFβR2 identify hair follicle bulge stem cells as the cell of origin for cutaneous squamous cell carcinoma. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 1506. doi:10.1158/1538-7445.AM2015-1506

Lysyl oxidase activity regulates oncogenic stress response and tumorigenesis

Cellular senescence, a stable proliferation arrest, is induced in response to various stresses. Oncogenic stress-induced senescence (OIS) results in blocked proliferation and constitutes a fail-safe program counteracting tumorigenesis. The events that enable a tumor in a benign senescent state to escape from OIS and become malignant are largely unknown. We show that lysyl oxidase activity contributes to the decision to maintain senescence. Indeed, in human epithelial cell the constitutive expression of the LOX or LOXL2 protein favored OIS escape, whereas inhibition of lysyl oxidase activity was found to stabilize OIS. The relevance of these in vitro observations is supported by in vivo findings: in a transgenic mouse model of aggressive pancreatic ductal adenocarcinoma (PDAC), increasing lysyl oxidase activity accelerates senescence escape, whereas inhibition of lysyl oxidase activity was found to stabilize senescence, delay tumorigenesis, and increase survival. Mechanistically, we show that lysyl oxidase activity favors the escape of senescence by regulating the focal-adhesion kinase. Altogether, our results demonstrate that lysyl oxidase activity participates in primary tumor growth by directly impacting the senescence stability.

Isolation and culture of mouse primary pancreatic acinar cells

This protocol permits rapid isolation (in less than 1 hr) of murine pancreatic acini, making it possible to maintain them in culture for more than one week. More than 20 x 10(6) acinar cells can be obtained from a single murine pancreas. This protocol offers the possibility to independently process as many as 10 pancreases in parallel. Because it preserves acinar architecture, this model is well suited for studying the physiology of the exocrine pancreas in vitro in contrast to cell lines established from pancreatic tumors, which display many genetic alterations resulting in partial or total loss of their acinar differentiation.

The conditional expression of KRAS G12D in mouse pancreas induces disorganization of endocrine islets prior the onset of ductal pre-cancerous lesions

BACKGROUND/OBJECTIVES

Pdx1-Cre; LSL-KRAS(G12D) mice develop premalignant pancreatic ductal lesions that can possibly progress spontaneously to pancreatic ductal adenocarcinoma (PDAC). Although Pdx1-Cre is expressed in the embryonic endoderm, which gives rise to all pancreatic lineages, the possible consequences of KRAS(G12D) expression in the endocrine compartment have never been finely explored.

METHODS

We examined by histology whether Pdx1-driven expression of KRAS(G12D) could induce islets of Langerhans defects.

RESULTS

We observed in Pdx1-Cre; LSL-KRAS(G12D) early disorganization of the endocrine compartment including i) hyperplasia affecting all the endocrine lineages, ii) ectopic onset of Ck19-positive (ductal-like) structures within the endocrine islets, and iii) the presence of islet cells co-expressing glucagon and insulin, all occurring before the onset of ducts lesions.

CONCLUSIONS

This work indicates that expression of KRAS(G12D) in Pdx1-expressing cells during embryogenesis affects the endocrine pancreas, and highlights the need to deepen possible consequences on both glucose metabolism and PDAC initiation.

Tif1γ suppresses murine pancreatic tumoral transformation by a Smad4-independent pathway

Transcriptional intermediary factor 1γ (TIF1γ; alias, TRIM33/RFG7/PTC7/ectodermin) belongs to an evolutionarily conserved family of nuclear factors that have been implicated in stem cell pluripotency, embryonic development, and tumor suppression. TIF1γ expression is markedly down-regulated in human pancreatic tumors, and Pdx1-driven Tif1γ inactivation cooperates with the Kras(G12D) oncogene in the mouse pancreas to induce intraductal papillary mucinous neoplasms. In this study, we report that aged Pdx1-Cre; LSL-Kras(G12D); Tif1γ(lox/lox) mice develop pancreatic ductal adenocarcinomas (PDACs), an aggressive and always fatal neoplasm, demonstrating a Tif1γ tumor-suppressive function in the development of pancreatic carcinogenesis. Deletion of SMAD4/DPC4 (deleted in pancreatic carcinoma locus 4) occurs in approximately 50% of human cases of PDAC. We, therefore, assessed the genetic relationship between Tif1γ and Smad4 signaling in pancreatic tumors and found that Pdx1-Cre; LSL-Kras(G12D); Smad4(lox/lox); Tif1γ(lox/lox) (alias, KSSTT) mutant mice exhibit accelerated tumor progression. Consequently, Tif1γ tumor-suppressor effects during progression from a premalignant to a malignant state in our mouse model of pancreatic cancer are independent of Smad4. These findings establish, for the first time to our knowledge, that Tif1γ and Smad4 both regulate an intraductal papillary mucinous neoplasm-to-PDAC sequence through distinct tumor-suppressor programs.

A rapid strategy to detect the recombined allele in LSL-TβRICA transgenic mice

We have previously generated a transgenic mouse strain (LSL-TβRI(CA)) containing a Cre-inducible constitutively active TGFβ type I receptor (Bartholin et al., 2008, Genesis 46: 724-731). Transgene expression depends on the excision of a floxed-transcriptional STOP (LSL, Lox-STOP-Lox) located upstream the TβRI(CA) coding sequence. To evaluate the correct excision of the STOP signal in the presence of Cre-recombinase, we developed a rapid screening based on an original PCR genotyping strategy. More precisely, we designed a set of primers flanking the LSL containing region. The size of the amplified products will differ according to recombination status of the LSL-TβRI(CA) allele. Indeed, the size of the STOP containing PCR product is 1.93 kb, but is reduced to 0.35 kb when the STOP signal is removed after Cre-mediated recombination. We validated excision in several compartments, including pancreas, liver, T lymphocytes, and embryos using different Cre expressing transgenic mouse strains. This represents a simple and efficient way of monitoring the tissue specific recombination of the LSL-TβRI(CA) allele.

Inactivation of TIF1gamma cooperates with Kras to induce cystic tumors of the pancreas

Inactivation of the Transforming Growth Factor Beta (TGFbeta) tumor suppressor pathway contributes to the progression of Pancreatic Ductal AdenoCarcinoma (PDAC) since it is inactivated in virtually all cases of this malignancy. Genetic lesions inactivating this pathway contribute to pancreatic tumor progression in mouse models. Transcriptional Intermediary Factor 1 gamma (TIF1gamma) has recently been proposed to be involved in TGFbeta signaling, functioning as either a positive or negative regulator of the pathway. Here, we addressed the role of TIF1gamma in pancreatic carcinogenesis. Using conditional Tif1gamma knockout mice (Tif1gamma(lox/lox)), we selectively abrogated Tif1gamma expression in the pancreas of Pdx1-Cre;Tif1gamma(lox/lox) mice. We also generated Pdx1-Cre;LSL-Kras(G12D);Tif1gamma(lox/lox) mice to address the effect of Tif1gamma loss-of-function in precancerous lesions induced by oncogenic Kras(G12D). Finally, we analyzed TIF1gamma expression in human pancreatic tumors. In our mouse model, we showed that Tif1gamma was dispensable for normal pancreatic development but cooperated with Kras activation to induce pancreatic tumors reminiscent of human Intraductal Papillary Mucinous Neoplasms (IPMNs). Interestingly, these cystic lesions resemble those observed in Pdx1-Cre;LSL-Kras(G12D);Smad4(lox/lox) mice described by others. However, distinctive characteristics, such as the systematic presence of endocrine pseudo-islets within the papillary projections, suggest that SMAD4 and TIF1gamma don't have strictly redundant functions. Finally, we report that TIF1gamma expression is markedly down-regulated in human pancreatic tumors by quantitative RT-PCR and immunohistochemistry supporting the relevance of these findings to human malignancy. This study suggests that TIF1gamma is critical for tumor suppression in the pancreas, brings new insight into the genetics of pancreatic cancer, and constitutes a promising model to decipher the respective roles of SMAD4 and TIF1gamma in the multifaceted functions of TGFbeta in carcinogenesis and development.

Inactivation of TIF1gamma cooperates with Kras to induce cystic tumors of the pancreas

Inactivation of the Transforming Growth Factor Beta (TGFβ) tumor suppressor pathway contributes to the progression of Pancreatic Ductal AdenoCarcinoma (PDAC) since it is inactivated in virtually all cases of this malignancy. Genetic lesions inactivating this pathway contribute to pancreatic tumor progression in mouse models. Transcriptional Intermediary Factor 1 gamma (TIF1γ) has recently been proposed to be involved in TGFβ signaling, functioning as either a positive or negative regulator of the pathway. Here, we addressed the role of TIF1γ in pancreatic carcinogenesis. Using conditional Tif1γ knockout mice (Tif1γ^lox/lox), we selectively abrogated Tif1γ expression in the pancreas of Pdx1-Cre;Tif1γ^lox/lox mice. We also generated Pdx1-Cre;LSL-Kras^G12D;Tif1γ^lox/lox mice to address the effect of Tif1γ loss-of-function in precancerous lesions induced by oncogenic Kras^G12D. Finally, we analyzed TIF1γ expression in human pancreatic tumors. In our mouse model, we showed that Tif1γ was dispensable for normal pancreatic development but cooperated with Kras activation to induce pancreatic tumors reminiscent of human Intraductal Papillary Mucinous Neoplasms (IPMNs). Interestingly, these cystic lesions resemble those observed in Pdx1-Cre;LSL-Kras^G12D;Smad4^lox/lox mice described by others. However, distinctive characteristics, such as the systematic presence of endocrine pseudo-islets within the papillary projections, suggest that SMAD4 and TIF1γ don't have strictly redundant functions. Finally, we report that TIF1γ expression is markedly down-regulated in human pancreatic tumors by quantitative RT–PCR and immunohistochemistry supporting the relevance of these findings to human malignancy. This study suggests that TIF1γ is critical for tumor suppression in the pancreas, brings new insight into the genetics of pancreatic cancer, and constitutes a promising model to decipher the respective roles of SMAD4 and TIF1γ in the multifaceted functions of TGFβ in carcinogenesis and development.

Inactivation of the TGFβ tumor suppressor pathway contributes to the progression of Pancreatic Ductal AdenoCarcinoma (PDAC), a devastating malignancy. Transcriptional Intermediary Factor 1γ (TIF1γ) has recently been proposed to be involved in TGFβ signaling, a pathway inactivated in virtually all cases of this malignancy. To address the role of TIF1γ in pancreatic carcinogenesis, we used conditional Tif1γ knockout mice. In a genetic background expressing a constitutively active mutation of KRAS oncogene (Kras^G12D) recurrently found in patients with PDAC, Tif1γ inactivation induces pancreatic precancerous lesions resembling those observed in the absence of Smad4, a key player involved TGFβ signal transduction. This observation strengthens the notion that TIF1γ plays an active role in TGFβ signaling. Interestingly, we also found that TIF1γ expression was markedly down-regulated in human pancreatic tumors supporting the relevance of our findings to human malignancy. Characterization of new players involved in the outbreak of early pancreatic lesions that will eventually evolve into invasive pancreatic cancer is crucial to detect the disease earlier and eventually develop new therapeutic drugs.