Sam C. Wang

KRAS, Hedgehog, Wnt and the twisted developmental biology of pancreatic ductal adenocarcinoma

Pancreatic ductal adenocarcinoma (PDAC) is characterized by near-universal mutations in KRAS and frequent deregulation of crucial embryonic signalling pathways, including the Hedgehog (Hh) and Wnt–β-catenin cascades. The creation of mouse models that closely resemble the human disease has provided a platform to better understand when and in which cell types these pathways are misregulated during PDAC development. Here we examine the central part that KRAS plays in the biology of PDAC, and how the timing and location of Hh and Wnt–β-catenin signalling dictate the specification and oncogenic properties of PDAC.

Stat3 and MMP7 Contribute to Pancreatic Ductal Adenocarcinoma Initiation and Progression

Chronic pancreatitis is a well-known risk factor for pancreatic ductal adenocarcinoma (PDA) development in humans, and inflammation promotes PDA initiation and progression in mouse models of the disease. However, the mechanistic link between inflammatory damage and PDA initiation is unclear. Using a Kras-driven mouse model of PDA, we establish that the inflammatory mediator Stat3 is a critical component of spontaneous and pancreatitis-accelerated PDA precursor formation and supports cell proliferation, metaplasia-associated inflammation, and MMP7 expression during neoplastic development. Furthermore, we show that Stat3 signaling enforces MMP7 expression in PDA cells and that MMP7 deletion limits tumor size and metastasis in mice. Finally, we demonstrate that serum MMP7 level in human patients with PDA correlated with metastatic disease and survival.

β-catenin blocks Kras-dependent reprogramming of acini into pancreatic cancer precursor lesions in mice

Cellular plasticity in adult organs is involved in both regeneration and carcinogenesis. WT mouse acinar cells rapidly regenerate following injury that mimics acute pancreatitis, a process characterized by transient reactivation of pathways involved in embryonic pancreatic development. In contrast, such injury promotes the development of pancreatic ductal adenocarcinoma (PDA) precursor lesions in mice expressing a constitutively active form of the GTPase, Kras, in the exocrine pancreas. The molecular environment that mediates acinar regeneration versus the development of PDA precursor lesions is poorly understood. Here, we used genetically engineered mice to demonstrate that mutant Kras promotes acinar-to-ductal metaplasia (ADM) and pancreatic cancer precursor lesion formation by blocking acinar regeneration following acute pancreatitis. Our results indicate that beta-catenin is required for efficient acinar regeneration. In addition, canonical beta-catenin signaling, a pathway known to regulate embryonic acinar development, is activated following acute pancreatitis. This regeneration-associated activation of beta-catenin signaling was not observed during the initiation of Kras-induced acinar-to-ductal reprogramming. Furthermore, stabilized beta-catenin signaling antagonized the ability of Kras to reprogram acini into PDA preneoplastic precursors. Therefore, these results suggest that beta-catenin signaling is a critical determinant of acinar plasticity and that it is inhibited during Kras-induced fate decisions that specify PDA precursors, highlighting the importance of temporal regulation of embryonic signaling pathways in the development of neoplastic cell fates.

Telomere attrition and Chk2 activation in human heart failure

The “postmitotic” phenotype in adult cardiac muscle exhibits similarities to replicative senescence more generally and constitutes a barrier to effective restorative growth in heart disease. Telomere dysfunction is implicated in senescence and apoptotic signaling but its potential role in heart disorders is unknown. Here, we report that cardiac apoptosis in human heart failure is associated specifically with defective expression of the telomere repeat- binding factor TRF2, telomere shortening, and activation of the DNA damage checkpoint kinase, Chk2. In cultured cardiomyocytes, interference with either TRF2 function or expression triggered telomere erosion and apoptosis, indicating that cell death can occur via this pathway even in postmitotic, noncycling cells; conversely, exogenous TRF2 conferred protection from oxidative stress. In vivo, mechanical stress was sufficient to down-regulate TRF2, shorten telomeres, and activate Chk2 in mouse myocardium, and transgenic expression of telomerase reverse transcriptase conferred protection from all three responses. Together, these data suggest that apoptosis in chronic heart failure is mediated in part by telomere dysfunction and suggest an essential role for TRF2 even in postmitotic cells.

Activation of cardiac Cdk9 represses PGC-1 and confers a predisposition to heart failure.

Hypertrophy allows the heart to adapt to workload but culminates in later pump failure; how it is achieved remains uncertain. Previously, we showed that hypertrophy is accompanied by activation of cyclin T/Cdk9, which phosphorylates the C‐terminal domain of the large subunit of RNA polymerase II, stimulating transcription elongation and pre‐mRNA processing; Cdk9 activity was required for hypertrophy in culture, whereas heart‐specific activation of Cdk9 by cyclin T1 provoked hypertrophy in mice. Here, we report that αMHC‐cyclin T1 mice appear normal at baseline yet suffer fulminant apoptotic cardiomyopathy when challenged by mechanical stress or signaling by the G‐protein Gq. At pathophysiological levels, Cdk9 activity suppresses many genes for mitochondrial proteins including master regulators of mitochondrial function (peroxisome proliferator‐activated receptor gamma coactivator 1 (PGC‐1), nuclear respiratory factor‐1). In culture, cyclin T1/Cdk9 suppresses PGC‐1, decreases mitochondrial membrane potential, and sensitizes cardiomyocytes to apoptosis, effects rescued by exogenous PGC‐1. Cyclin T1/Cdk9 inhibits PGC‐1 promoter activity and preinitiation complex assembly. Thus, chronic activation of Cdk9 causes not only cardiomyocyte enlargement but also defective mitochondrial function, via diminished PGC‐1 transcription, and a resulting susceptibility to apoptotic cardiomyopathy.

Lymph node sampling rates and predictors of nodal metastasis in pancreatic neuroendocrine tumor resections: the UCSF experience with 149 patients.

Objectives The decision to perform pancreas-preserving procedures or standard resections for pancreatic neuroendocrine tumors (PNETs) is often based on the perceived risk of malignancy, including potential nodal involvement. We sought to identify clinicopathological factors that predict nodal disease. Methods This is a retrospective review of pathology database for PNET resections from January 1, 1988, to March 15, 2010. Univariate analysis and multivariate logistic regression were used to identify predictors of nodal metastasis. Results A total of 149 patients were identified. Enucleations had lower lymph node sampling rates compared to major resections. Excluding enucleations, 23% of patients had no lymph nodes sampled. For patients who did have lymph nodes evaluated, a median of 5 lymph nodes were examined. On multivariate analysis, only distant disease predicted nodal metastasis (odds ratio = 3.80, P = 0.02); tumor size did not (P = 0.48). One third of patients with lymph node metastasis had tumors less than 3 cm. Conclusions Lymph nodes are not evaluated in many major pancreatic resections for PNET, and preoperative prediction of nodal metastasis is difficult, even when tumor size is considered. Consequently, many patients may be understaged and undergo potentially inadequate resection. Inconsistent lymph node sampling may explain conflicting conclusions in the literature regarding the prognostic value of lymph node involvement in PNET patients.

Neoadjuvant Therapy Followed by Resection Versus Upfront Resection for Resectable Pancreatic Cancer: A Propensity Score Matched Analysis

Purpose To compare overall survival between patients who received neoadjuvant therapy (NAT) followed by resection and those who received upfront resection (UR)-as well as a subgroup of UR patients who also received adjuvant therapy-for early-stage resectable pancreatic adenocarcinoma. Patients and Methods Adult patients with resected, clinical stage I or II adenocarcinoma of the head of the pancreas were identified in the National Cancer Database from 2006 to 2012. Patients who underwent NAT followed by curative-intent resection were matched by propensity score with patients whose tumors were resected upfront. Overall survival was compared by using a Cox proportional hazards regression model. Early postoperative and oncologic outcomes were evaluated. Results We identified 15,237 patients with clinical stage I or II resected pancreatic head adenocarcinoma. From the NAT group, 2,005 patients (95%) were matched with 6,015 patients who underwent UR. The NAT group was associated with improved survival compared with UR (median survival, 26 months v 21 months, respectively; stratified log-rank P < .01; hazard ratio, 0.72; 95% CI, 0.68 to 0.78). Patients in the UR group had higher pathologic T stage (pT3 and T4: 86% v 73%; P < .01), higher positive lymph nodes (73% v 48%; P < .01), and higher positive resection margin (24% v 17%; P < .01). Compared with a subset of UR patients who received adjuvant therapy, NAT patients had a better survival (adjusted hazard ratio, 0.83; 95% CI, 0.73 to 0.89). Conclusion NAT followed by resection has a significant survival benefit compared with UR in early-stage, resected pancreatic head adenocarcinoma. These findings support the use of NAT, particularly as a patient selection tool, in the management of resectable pancreatic adenocarcinoma.

Pretreatment Neutrophil to Lymphocyte Ratio Independently Predicts Disease-specific Survival in Resectable Gastroesophageal Junction and Gastric Adenocarcinoma.

Objective:Preoperative methods to estimate disease-specific survival (DSS) for resectable gastroesophageal (GE) junction and gastric adenocarcinoma are limited. We evaluated the relationship between DSS and pretreatment neutrophil to lymphocyte ratio (NLR). Background:The patients inflammatory state is thought to be associated with oncologic outcomes, and NLR has been used as a simple and convenient marker for the systemic inflammatory response. Previous studies have suggested that NLR is associated with cancer-specific outcomes. Methods:A retrospective review of a prospectively maintained institutional database was undertaken to identify patients who underwent potentially curative resection for GE junction and gastric adenocarcinoma from 1998 to 2013. Clinicopathologic findings, pretreatment leukocyte values, and follow-up status were recorded. The Kaplan-Meier method was used to estimate DSS, and Cox proportional hazards models were used to evaluate the association between variables and DSS. Results:We identified 1498 patients who fulfilled our eligibility criteria. Univariate analysis showed that male sex, Caucasian race, increased T and N stage, GE junction location, moderate/poor differentiation, nonintestinal Lauren histology, and vascular and perineural invasion were associated with worse DSS. Elevated NLR was also associated with worse DSS [hazard ratio (HR) = 1.11; 95% CI: 1.08–1.14; P < 0.01]. On multivariate analysis, pretreatment NLR as a continuous variable was a highly significant independent predictor of DSS. For every unit increase in NLR, the risk of cancer-associated death increases by approximately 10% (HR = 1.10; 95% CI: 1.05–1.13; P < 0.0001). Conclusions:In patients with resectable GE junction and gastric adenocarcinoma, pretreatment NLR independently predicts DSS. This and other clinical variables can be used in conjunction with cross-sectional imaging and endoscopic ultrasound as part of the preoperative risk stratification process.

Suppression of the SWI/SNF Component Arid1a Promotes Mammalian Regeneration

Mammals have partially lost the extensive regenerative capabilities of some vertebrates, possibly as a result of chromatin-remodeling mechanisms that enforce terminal differentiation. Here, we show that deleting the SWI/SNF component Arid1a substantially improves mammalian regeneration. Arid1a expression is suppressed in regenerating tissues, and genetic deletion of Arid1a increases tissue repair following an array of injuries. Arid1a deficiency in the liver increases proliferation, reduces tissue damage and fibrosis, and improves organ function following surgical resection and chemical injuries. Hepatocyte-specific deletion is also sufficient to increase proliferation and regeneration without excessive overgrowth, and global Arid1a disruption potentiates soft tissue healing in the ear. We show that Arid1a loss reprograms chromatin to restrict promoter access by transcription factors such as C/ebpα, which enforces differentiation, and E2F4, which suppresses cell-cycle re-entry. Thus, epigenetic reprogramming mediated by deletion of a single gene improves mammalian regeneration and suggests strategies to promote tissue repair after injury.

Precise let-7 expression levels balance organ regeneration against tumor suppression

The in vivo roles for even the most intensely studied microRNAs remain poorly defined. Here, analysis of mouse models revealed that let-7, a large and ancient microRNA family, performs tumor suppressive roles at the expense of regeneration. Too little or too much let-7 resulted in compromised protection against cancer or tissue damage, respectively. Modest let-7 overexpression abrogated MYC-driven liver cancer by antagonizing multiple let-7 sensitive oncogenes. However, the same level of overexpression blocked liver regeneration, while let-7 deletion enhanced it, demonstrating that distinct let-7 levels can mediate desirable phenotypes. let-7 dependent regeneration phenotypes resulted from influences on the insulin-PI3K-mTOR pathway. We found that chronic high-dose let-7 overexpression caused liver damage and degeneration, paradoxically leading to tumorigenesis. These dose-dependent roles for let-7 in tissue repair and tumorigenesis rationalize the tight regulation of this microRNA in development, and have important implications for let-7 based therapeutics. DOI: http://dx.doi.org/10.7554/eLife.09431.001