Dual-specificity phosphatase 5 controls the localized inhibition, propagation, and transforming potential of ERK signaling

Deregulated extracellular signal-regulated kinase (ERK) signaling drives cancer growth. Normally, ERK activity is self-limiting by the rapid inactivation of upstream kinases and delayed induction of dual-specificity MAP kinase phosphatases (MKPs/DUSPs). However, interactions between these feedback mechanisms are unclear. Here we show that, although the MKP DUSP5 both inactivates and anchors ERK in the nucleus, it paradoxically increases and prolongs cytoplasmic ERK activity. The latter effect is caused, at least in part, by the relief of ERK-mediated RAF inhibition. The importance of this spatiotemporal interaction between these distinct feedback mechanisms is illustrated by the fact that expression of oncogenic BRAF(V600E), a feedback-insensitive mutant RAF kinase, reprograms DUSP5 into a cell-wide ERK inhibitor that facilitates cell proliferation and transformation. In contrast, DUSP5 deletion causes BRAF(V600E)-induced ERK hyperactivation and cellular senescence. Thus, feedback interactions within the ERK pathway can regulate cell proliferation and transformation, and suggest oncogene-specific roles for DUSP5 in controlling ERK signaling and cell fate

Suppression of mutant Kirsten-RAS (KRASG12D)-driven pancreatic carcinogenesis by dual-specificity MAP kinase phosphatases 5 and 6

The cytoplasmic phosphatase DUSP6 and its nuclear counterpart DUSP5 are negative regulators of RAS/ERK signalling. Here we use deletion of either Dusp5 or Dusp6 to explore the roles of these phosphatases in a murine model of KRASG12D-driven pancreatic cancer. By 56-days, loss of either DUSP5 or DUSP6 causes a significant increase in KRASG12D-driven pancreatic hyperplasia. This is accompanied by increased pancreatic acinar to ductal metaplasia (ADM) and the development of pre-neoplastic pancreatic intraepithelial neoplasia (PanINs). In contrast, by 100-days, pancreatic hyperplasia is reversed with significant atrophy of pancreatic tissue and weight loss observed in animals lacking either DUSP5 or DUSP6. On further ageing, Dusp6−/− mice display accelerated development of metastatic pancreatic ductal adenocarcinoma (PDAC), while in Dusp5−/− animals, although PDAC development is increased this process is attenuated by atrophy of pancreatic acinar tissue and severe weight loss in some animals before cancer could progress. Our data suggest that despite a common target in the ERK MAP kinase, DUSP5 and DUSP6 play partially non-redundant roles in suppressing oncogenic KRASG12D signalling, thus retarding both tumour initiation and progression. Our data suggest that loss of either DUSP5 or DUSP6, as observed in certain human tumours, including the pancreas, could promote carcinogenesis

Functional analysis of B-Raf complexes and the role of Raf heterodimers

EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Regulation and Role of Raf-1/B-Raf Heterodimerization

The Ras-Raf-MEK-extracellular signal-regulated kinase (ERK) pathway participates in the control of many fundamental cellular processes including proliferation, survival, and differentiation. The pathway is deregulated in up to 30% of human cancers, often due to mutations in Ras and the B-Raf isoform. Raf-1 and B-Raf can form heterodimers, and this may be important for cellular transformation. Here, we have analyzed the biochemical and biological properties of Raf-1/B-Raf heterodimers. Isolated Raf-1/B-Raf heterodimers possessed a highly increased kinase activity compared to the respective homodimers or monomers. Heterodimers between wild-type Raf-1 and B-Raf mutants with low or no kinase activity still displayed elevated kinase activity, as did heterodimers between wild-type B-Raf and kinase-negative Raf-1. In contrast, heterodimers containing both kinase-negative Raf-1 and kinase-negative B-Raf were completely inactive, suggesting that the kinase activity of the heterodimer specifically originates from Raf and that either kinase-competent Raf isoform is sufficient to confer high catalytic activity to the heterodimer. In cell lines, Raf-1/B-Raf heterodimers were found at low levels. Heterodimerization was enhanced by 14-3-3 proteins and by mitogens independently of ERK. However, ERK-induced phosphorylation of B-Raf on T753 promoted the disassembly of Raf heterodimers, and the mutation of T753 prolonged growth factor-induced heterodimerization. The B-Raf T753A mutant enhanced differentiation of PC12 cells, which was previously shown to be dependent on sustained ERK signaling. Fine mapping of the interaction sites by peptide arrays suggested a complex mode of interaction involving multiple contact sites with a main Raf-1 binding site in B-Raf encompassing T753. In summary, our data suggest that Raf-1/B-Raf heterodimerization occurs as part of the physiological activation process and that the heterodimer has distinct biochemical properties that may be important for the regulation of some biological processes

Dual-specificity phosphatase 5 regulates nuclear ERK activity and suppresses skin cancer by inhibiting mutant Harvey-Ras (HRas^Q61L)-driven SerpinB2 expression

Ectopic expression of dual-specificity phosphatase 5 (DUSP5), an inducible mitogen-activated protein (MAP) kinase phosphatase, specifically inactivates and anchors extracellular signal-regulated kinase (ERK)1/2 in the nucleus. However, the role of endogenous DUSP5 in regulating the outcome of Ras/ERK kinase signaling under normal and pathological conditions is unknown. Here we report that mice lacking DUSP5 show a greatly increased sensitivity to mutant Harvey-Ras (HRas(Q61L))-driven papilloma formation in the 7,12-Dimethylbenz[a]anthracene/12-O-tetradecanoylphorbol-13-acetate (DMBA/TPA) model of skin carcinogenesis. Furthermore, mouse embryo fibroblasts (MEFs) from DUSP5(−/−) mice show increased levels of nuclear phospho-ERK immediately after TPA stimulation and fail to accumulate total ERK in the nucleus compared with DUSP5(+/+) cells. Surprisingly, a microarray analysis reveals that only a small number of Ras/ERK-dependent TPA-responsive transcripts are up-regulated on deletion of DUSP5 in MEFs and mouse skin. The most up-regulated gene on DUSP5 loss encodes SerpinB2, an inhibitor of extracellular urokinase plasminogen activator and deletion of DUSP5 acts synergistically with mutant HRas(Q61L) and TPA to activate ERK-dependent SerpinB2 expression at the transcriptional level. SerpinB2 has previously been implicated as a mediator of DMBA/TPA-induced skin carcinogenesis. By analyzing DUSP5(−/−), SerpinB2(−/−) double knockout mice, we demonstrate that deletion of SerpinB2 abrogates the increased sensitivity to papilloma formation seen on DUSP5 deletion. We conclude that DUSP5 performs a key nonredundant role in regulating nuclear ERK activation, localization, and gene expression. Furthermore, our results suggest an in vivo role for DUSP5 as a tumor suppressor by modulating the oncogenic potential of activated Ras in the epidermis

Phase II proof of concept study of atorvastatin in castration resistant prostate cancer

Objectives: To test for evidence of statin-mediated effects in patients with castration resistant prostate cancer as post-diagnosis use of statins in patients with prostate cancer is associated with favourable survival outcome. Enhanced tumoral cholesterol uptake can drive castration resistant prostate cancer (CRPC). However, it remains unclear whether these associations result from confounding factors or directly from statin mediated effects. Patients and Methods: The SPECTRE trial was a 6-weeks long proof-of-concept single-arm Phase II treatment trial combining atorvastatin and androgen deprivation therapy in patients with CRPC (regardless of the metastatic status), designed to test for evidence of statin-mediated effects in patients with CRPC. The primary study endpoint was the proportion of patients achieving ≥50% drop from baseline in PSA levels at any time over the 6-week period of atorvastatin medication (PSA response). Exploratory endpoints include PSA velocity and mass spectrometrically identified serum metabolites. Results: At scheduled interim analysis, one of twelve patients experienced a ≥50% drop in PSA levels (primary endpoint), with ≥2 patients satisfying the primary endpoint required for further recruitment. All 12 experienced substantial falls in serum cholesterol levels following statin treatment. While all patients had comparable pre-study PSA velocities, 6 of 12 patients showed decreased PSA velocities following statin treatment, suggestive of disease stablisation. Unbiased metabolomics analysis on serial weekly blood samples identified tryptophan to be the dominant metabolite associated with patient response to statin. Conclusions: Data from the SPECTRE study provides the first evidence of statin mediated effects on CRPC and early sign of disease stabilisation. Our data also highlights the possibility of altered tryptophan metabolism being associated with tumour response

Cyclocreatine suppresses creatine metabolism and impairs prostate cancer progression

Prostate cancer is the second most common cause of cancer mortality in men worldwide. Applying a novel genetically engineered mouse model (GEMM) of aggressive prostate cancer driven by deficiency of the tumour suppressors PTEN and SPRY2 (Sprouty 2), we identified enhanced creatine metabolism as a central component of progressive disease. Creatine treatment was associated with enhanced cellular basal respiration in vitro and increased tumour cell proliferation in vivo. Stable isotope tracing revealed that intracellular levels of creatine in prostate cancer cells are predominantly dictated by exogenous availability rather than by de novo synthesis from arginine. Genetic silencing of creatine transporter SLC6A8 depleted intracellular creatine levels and reduced the colony-forming capacity of human prostate cancer cells. Accordingly, in vitro treatment of prostate cancer cells with cyclocreatine, a creatine analog, dramatically reduced intracellular levels of creatine and its derivatives phosphocreatine and creatinine and suppressed proliferation. Supplementation with cyclocreatine impaired cancer progression in the PTEN and SPRY-deficient prostate cancer GEMMs and in a xenograft liver metastasis model. Collectively, these results identify a metabolic vulnerability in prostate cancer and demonstrate a rational therapeutic strategy to exploit this vulnerability to impede tumour progression

Activation of β-catenin cooperates with loss of Pten to drive AR-independent castration-resistant prostate cancer

Inhibition of the androgen receptor (AR) is the main strategy to treat advanced prostate cancers. AR-independent treatment-resistant prostate cancer is a major unresolved clinical problem. Prostate cancer patients with alterations in canonical WNT pathway genes, which lead to β-catenin activation, are refractory to AR-targeted therapies. Here using clinically relevant murine prostate cancer models, we investigated the significance of β-catenin activation in prostate cancer progression and treatment resistance. β-catenin activation, independent of the cell-of-origin, cooperated with Pten loss to drive AR-independent castration-resistant prostate cancer. Prostate tumours with β-catenin activation relied on the non-canonical WNT ligand WNT5a for sustained growth. WNT5a repressed AR expression and maintained the expression of c-Myc, an oncogenic effector of β-catenin activation, by mediating nuclear localization of NFƙBp65 and β-catenin. Overall, WNT/β-catenin and AR signalling are reciprocally inhibited. Therefore, inhibiting WNT/β-catenin signalling by limiting WNT secretion in concert with AR inhibition may be useful for treating prostate cancers with alterations in WNT pathway genes