Colin Nixon

p53 status determines the role of autophagy in pancreatic tumour development

Macroautophagy (hereafter referred to as autophagy) is a process in which organelles termed autophagosomes deliver cytoplasmic constituents to lysosomes for degradation. Autophagy has a major role in cellular homeostasis and has been implicated in various forms of human disease. The role of autophagy in cancer seems to be complex, with reports indicating both pro-tumorigenic and tumour-suppressive roles. Here we show, in a humanized genetically-modified mouse model of pancreatic ductal adenocarcinoma (PDAC), that autophagy’s role in tumour development is intrinsically connected to the status of the tumour suppressor p53. Mice with pancreases containing an activated oncogenic allele of Kras (also called Ki-Ras)—the most common mutational event in PDAC—develop a small number of pre-cancerous lesions that stochastically develop into PDAC over time. However, mice also lacking the essential autophagy genes Atg5 or Atg7 accumulate low-grade, pre-malignant pancreatic intraepithelial neoplasia lesions, but progression to high-grade pancreatic intraepithelial neoplasias and PDAC is blocked. In marked contrast, in mice containing oncogenic Kras and lacking p53, loss of autophagy no longer blocks tumour progression, but actually accelerates tumour onset, with metabolic analysis revealing enhanced glucose uptake and enrichment of anabolic pathways, which can fuel tumour growth. These findings provide considerable insight into the role of autophagy in cancer and have important implications for autophagy inhibition in cancer therapy. In this regard, we also show that treatment of mice with the autophagy inhibitor hydroxychloroquine, which is currently being used in several clinical trials, significantly accelerates tumour formation in mice containing oncogenic Kras but lacking p53.

The chemokine receptor D6 limits the inflammatory response in vivo.

How the inflammatory response is initiated has been well defined but relatively little is known about how such responses are resolved. Here we show that the D6 chemokine receptor is involved in the post-inflammatory clearance of β-chemokines from cutaneous sites. After induction of inflammation by phorbol esters, wild-type mice showed a transient inflammatory response. However, in D6-deficient mice, an excess concentration of residual chemokines caused a notable inflammatory pathology with similarities to human psoriasis. These results suggest that D6 is involved in the resolution of the cutaneous inflammatory response.

Rab25 and CLIC3 Collaborate to Promote Integrin Recycling from Late Endosomes/Lysosomes and Drive Cancer Progression

Summary Here we show that Rab25 permits the sorting of ligand-occupied, active-conformation α5β1 integrin to late endosomes/lysosomes. Photoactivation and biochemical approaches show that lysosomally targeted integrins are not degraded but are retrogradely transported and recycled to the plasma membrane at the back of invading cells. This requires CLIC3, a protein upregulated in Rab25-expressing cells and tumors, which colocalizes with active α5β1 in late endosomes/lysosomes. CLIC3 is necessary for release of the cell rear during migration on 3D matrices and is required for invasion and maintenance of active Src signaling in organotypic microenvironments. CLIC3 expression predicts lymph node metastasis and poor prognosis in operable cases of pancreatic ductal adenocarcinoma (PDAC). The identification of CLIC3 as a regulator of a recycling pathway and as an independent prognostic indicator in PDAC highlights the importance of active integrin trafficking as a potential drive to cancer progression in vivo.

CXCR2 Inhibition Profoundly Suppresses Metastases and Augments Immunotherapy in Pancreatic Ductal Adenocarcinoma.

Summary CXCR2 has been suggested to have both tumor-promoting and tumor-suppressive properties. Here we show that CXCR2 signaling is upregulated in human pancreatic cancer, predominantly in neutrophil/myeloid-derived suppressor cells, but rarely in tumor cells. Genetic ablation or inhibition of CXCR2 abrogated metastasis, but only inhibition slowed tumorigenesis. Depletion of neutrophils/myeloid-derived suppressor cells also suppressed metastasis suggesting a key role for CXCR2 in establishing and maintaining the metastatic niche. Importantly, loss or inhibition of CXCR2 improved T cell entry, and combined inhibition of CXCR2 and PD1 in mice with established disease significantly extended survival. We show that CXCR2 signaling in the myeloid compartment can promote pancreatic tumorigenesis and is required for pancreatic cancer metastasis, making it an excellent therapeutic target.

LKB1 Haploinsufficiency Cooperates With Kras to Promote Pancreatic Cancer Through Suppression of p21-Dependent Growth Arrest

Background & Aims Patients carrying germline mutations of LKB1 have an increased risk of pancreatic cancer; however, it is unclear whether down-regulation of LKB1 is an important event in sporadic pancreatic cancer. In this study, we aimed to investigate the impact of LKB1 down-regulation for pancreatic cancer in mouse and human and to elucidate the mechanism by which Lkb1 deregulation contributes to this disease. Methods We first investigated the consequences of Lkb1 deficiency in a genetically modified mouse model of pancreatic cancer, both in terms of disease progression and at the molecular level. To test the relevance of our findings to human pancreatic cancer, we investigated levels of LKB1 and its potential targets in human pancreatic cancer. Results We definitively show that Lkb1 haploinsufficiency can cooperate with oncogenic KrasG12D to cause pancreatic ductal adenocarcinoma (PDAC) in the mouse. Mechanistically, this was associated with decreased p53/p21-dependent growth arrest. Haploinsufficiency for p21 (Cdkn1a) also synergizes with KrasG12D to drive PDAC in the mouse. We also found that levels of LKB1 expression were decreased in around 20% of human PDAC and significantly correlated with low levels of p21 and a poor prognosis. Remarkably, all tumors that had low levels of LKB1 had low levels of p21, and these tumors did not express mutant p53. Conclusions We have identified a novel LKB1-p21 axis that suppresses PDAC following Kras mutation in vivo. Down-regulation of LKB1 may therefore serve as an alternative to p53 mutation to drive pancreatic cancer in vivo.

N-WASP coordinates the delivery and F-actin–mediated capture of MT1-MMP at invasive pseudopods

N-WASP is critical for cancer cell invasion through its promotion of the trafficking and capture of MT1-MMP in invasive pseudopods.

TIGAR Is Required for Efficient Intestinal Regeneration and Tumorigenesis

Summary Regulation of metabolic pathways plays an important role in controlling cell growth, proliferation, and survival. TIGAR acts as a fructose-2,6-bisphosphatase, potentially promoting the pentose phosphate pathway to produce NADPH for antioxidant function and ribose-5-phosphate for nucleotide synthesis. The functions of TIGAR were dispensable for normal growth and development in mice but played a key role in allowing intestinal regeneration in vivo and in ex vivo cultures, where growth defects due to lack of TIGAR were rescued by ROS scavengers and nucleosides. In a mouse intestinal adenoma model, TIGAR deficiency decreased tumor burden and increased survival, while elevated expression of TIGAR in human colon tumors suggested that deregulated TIGAR supports cancer progression. Our study demonstrates the importance of TIGAR in regulating metabolism for regeneration and cancer development and identifies TIGAR as a potential therapeutic target in diseases such as ulcerative colitis and intestinal cancer.

Mutant K-Ras activation of the proapoptotic MST2 pathway is antagonized by wild-type K-Ras.

K-Ras mutations are frequent in colorectal cancer (CRC), albeit K-Ras is the only Ras isoform that can elicit apoptosis. Here, we show that mutant K-Ras directly binds to the tumor suppressor RASSF1A to activate the apoptotic MST2-LATS1 pathway. In this pathway LATS1 binds to and sequesters the ubiquitin ligase Mdm2 causing stabilization of the tumor suppressor p53 and apoptosis. However, mutant Ras also stimulates autocrine activation of the EGF receptor (EGFR) which counteracts mutant K-Ras-induced apoptosis. Interestingly, this protection requires the wild-type K-Ras allele, which inhibits the MST2 pathway in part via AKT activation. Confirming the pathophysiological relevance of the molecular findings, we find a negative correlation between K-Ras mutation and MST2 expression in human CRC patients and CRC mouse models. The small number of tumors with co-expression of mutant K-Ras and MST2 has elevated apoptosis rates. Thus, in CRC, mutant K-Ras transformation is supported by the wild-type allele.

Pyruvate carboxylation enables growth of SDH-deficient cells by supporting aspartate biosynthesis

Succinate dehydrogenase (SDH) is a heterotetrameric nuclear-encoded complex responsible for the oxidation of succinate to fumarate in the tricarboxylic acid cycle. Loss-of-function mutations in any of the SDH genes are associated with cancer formation. However, the impact of SDH loss on cell metabolism and the mechanisms enabling growth of SDH-defective cells are largely unknown. Here, we generated Sdhb-ablated kidney mouse cells and used comparative metabolomics and stable-isotope-labelling approaches to identify nutritional requirements and metabolic adaptations to SDH loss. We found that lack of SDH activity commits cells to consume extracellular pyruvate, which sustains Warburg-like bioenergetic features. We further demonstrated that pyruvate carboxylation diverts glucose-derived carbons into aspartate biosynthesis, thus sustaining cell growth. By identifying pyruvate carboxylase as essential for the proliferation and tumorigenic capacity of SDH-deficient cells, this study revealed a metabolic vulnerability for potential future treatment of SDH-associated malignancies.

ERK5 signalling in prostate cancer promotes an invasive phenotype.

Background:Aberrant mitogen/extracellular signal-regulated kinase 5 (MEK5)–extracellular signal-regulated protein kinase 5 (ERK5)-mediated signalling has been implicated in a number of tumour types including prostate cancer (PCa). The molecular basis of ERK5-driven carcinogenesis and its clinical relevance remain to be fully characterised.Methods:Modulation of ERK5 expression or function in human PCa PC3 and PC3–ERK5 (stably transfected with ERK5) cells was performed using siRNA-mediated knockdown or the MEK inhibitor PD18435 respectively. In vitro significance of ERK5 signalling was assessed by assays for proliferation, motility, invasion and invadopodia. Expression of matrix metalloproteinases/tissue inhibitors of metalloproteases was determined by Q-RT–PCR. Extracellular signal-regulated protein kinase 5 expression in primary and metastatic PCa was examined using immunohistochemistry.Results:Reduction of ERK5 expression or signalling significantly inhibited the motility and invasive capability of PC3 cells. Extracellular signal-regulated protein kinase 5-mediated signalling significantly promoted formation of in vivo metastasis in an orthotopic PCa model (P<0.05). Invadopodia formation was also enhanced by forced ERK5 expression in PC3 cells. Furthermore, in metastatic PCa, nuclear ERK5 immunoreactivity was significantly upregulated when compared with benign prostatic hyperplasia and primary PCa (P=0.013 and P<0.0001, respectively).Conclusion:Our in vitro, in vivo and clinical data support an important role for the MEK5–ERK5 signalling pathway in invasive PCa, which represents a potential target for therapy in primary and metastatic PCa.