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

The pro-tumourigenic role of epithelial TGFß 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 TGFß signalling. In the presence of concurrent Apc and Kras mutations, activation of epithelial TGFß 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 TGFß 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 TGFß 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 TGFß-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 TGFß signalling. Here, we describe a mouse model of right-sided colon cancer driven by oncogenic BRAF and loss of epithelial TGFß-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 TGFß-receptor signalling is instrumental in suppressing the tumorigenic potential of these foetal-like progenitor cells.

Generation of a conditional Flpo/FRT mouse model expressing constitutively active TGFß in fibroblasts.

Transforming growth factor (TGFß) is a secreted factor, which accumulates in tissues during many physio- and pathological processes such as embryonic development, wound healing, fibrosis and cancer. In order to analyze the effects of increased microenvironmental TGFß concentration in vivo, we developed a conditional transgenic mouse model (Flpo/Frt system) expressing bioactive TGFß in fibroblasts, a cell population present in the microenvironment of almost all tissues. To achieve this, we created the genetically-engineered [Fsp1-Flpo; FSFTGFßCA] mouse model. The Fsp1-Flpo allele consists in the Flpo recombinase under the control of the Fsp1 (fibroblast-specific promoter 1) promoter. The FSFTGFßCA allele consists in a transgene encoding a constitutively active mutant form of TGFß (TGFßCA) under the control of a Frt-STOP-Frt (FSF) cassette. The FSFTGFßCA allele was created to generate this model, and functionally validated by in vitro, ex vivo and in vivo techniques. [Fsp1-Flpo; FSFTGFßCA] animals do not present any obvious phenotype despite the correct expression of TGFßCA transgene in fibroblasts. This [Fsp1-Flpo; FSFTGFßCA] model is highly pertinent for future studies on the effect of increased microenvironmental bioactive TGFß concentrations in mice bearing Cre-dependent genetic alterations in other compartments (epithelial or immune compartments for instance). These dual recombinase system (DRS) approaches will enable scientists to study uncoupled spatiotemporal regulation of different genetic alterations within the same mouse, thus better replicating the complexity of human diseases.

Glandular defects in the mouse uterus with sustained activation of TGF-beta signaling is associated with altered differentiation of endometrial stromal cells and formation of stromal compartment.

Uterine gland development, also known as adenogenesis, is a key uterine morphogenic process indispensable for normal uterine function and fertility. Our earlier studies have reported that overactivation of TGFB receptor 1 (TGFBR1) in the mouse uterus using progesterone receptor (Pgr)-Cre recombinase causes female infertility, defective decidualization, and reduced uterine gland formation, a developmental milestone of postnatal uterus. To understand mechanisms that underpin the disrupted uterine gland formation in mice with sustained activation of TGFBR1, we raised the question of whether early postnatal adenogenesis was compromised in these mice. Experiments were designed using mice with constitutive activation of TGFBR1 driven by Pgr-Cre to determine the timing of adenogenic defects and potential mechanisms associated with dysregulation of adenogenic genes, luminal epithelial cell proliferation and endometrial fibrotic changes. Uterine tissues from mice with constitutive activation of TGFBR1 were collected during the critical time window of adenogenesis and analyzed together with age-matched controls. Multiple approaches including immunohistochemistry, immunofluorescence, Trichrome staining, quantitative real-time PCR, western blot, conditional knockout and human endometrial cell culture were utilized. TGFBR1 activation in the mouse uterus suppressed adenogenesis during postnatal uterine development, concomitant with the aberrant differentiation of uterine stromal cells. Analysis of transcript expression of WNT pathway components revealed dysregulation of adenogenesis-associated genes. Notably, the adenogenic defects occurred in spite of the increased proliferation of uterine luminal epithelial cells, accompanied by increased expression of genes associated with fibrotic changes. Moreover, the adenogenic defects were alleviated in mice where TGFBR1 was activated in presumably half of the complement of uterine cells. Our results suggest that altered differentiation of endometrial stromal cells and formation of stromal compartment promote adenogenic defects.

TGFß 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-ß1 (TGFß1) ligand. In acetaminophen poisoning, inhibition of TGFß receptor 1 (TGFßR1) improved mouse survival. TGFßR1 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.

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.

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 (TGFBR1CA) using Gdf9-iCre (termed TGFBR1-CAG9Cre) 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-CAG9Cre 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-CAG9Cre 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-CAG9Cre 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.

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

This corrects the article DOI: 10.1038/nature22056.

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

BACKGROUND & AIMS: Transforming growth factor beta (TGFß) acts either as a tumor suppressor or as an oncogene, depending on the cellular context and time of activation. TGFß activates the canonical SMAD pathway through its interaction with the serine/threonine kinase type I and II heterotetrameric receptors. Previous studies investigating TGFß-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 TGFß receptor (TßRICA) in the pancreatic acinar compartment. RESULTS: We observed that TßRICA 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 Hnf1ß, Sox9, and Hes1. CONCLUSIONS: We demonstrate that TGFß 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.

TGFß 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 TGFß signalling, a pathway commonly mutated in colorectal cancer (CRC). Genetic inactivation of TGFß 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, TGFß and blockade of these makes tumourigenesis more efficient from this compartment.

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-ß (TGFß) signalling in BRAF inhibitor drug-resistance mechanisms, but the potential for targeting TGFß signalling in cases of advanced melanoma has not been investigated. We show that mutant BRAFV600E confers an intrinsic dependence on TGFß/TGFß 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 TGFß 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 TGFß 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 TGFß 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 TGFß signalling, are driving events of skin tumorigenesis.

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

Despite the well-established tumor suppressive role of TGFß proteins, depletion of key TGFß signaling components in the mouse ovary does not induce a growth advantage. To define the role of TGFß signaling in ovarian tumorigenesis, we created a mouse model expressing a constitutively active TGFß 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.

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.