Characterization of a selective inhibitor of the Parkinson's disease kinase LRRK2.

Mutations in leucine-rich repeat kinase 2 (LRRK2) are strongly associated with late-onset autosomal dominant Parkinson's disease. We employed a new, parallel, compound-centric approach to identify a potent and selective LRRK2 inhibitor, LRRK2-IN-1, and demonstrated that inhibition of LRRK2 induces dephosphorylation of Ser910 and Ser935 and accumulation of LRRK2 within aggregate structures. LRRK2-IN-1 will serve as a versatile tool to pharmacologically interrogate LRRK2 biology and study its role in Parkinson's disease.

A crucial role of mitochondrial Hsp40 in preventing dilated cardiomyopathy.

Many heat-shock proteins (Hsp) are members of evolutionarily conserved families of chaperone proteins that inhibit the aggregation of unfolded polypeptides and refold denatured proteins, thereby remedying phenotypic effects that may result from protein aggregation or protein instability. Here we report that the mitochondrial chaperone Hsp40, also known as Dnaja3 or Tid1, is differentially expressed during cardiac development and pathological hypertrophy. Mice deficient in Dnaja3 developed dilated cardiomyopathy (DCM) and died before 10 weeks of age. Progressive respiratory chain deficiency and decreased copy number of mitochondrial DNA were evident in cardiomyocytes lacking Dnaja3. Profiling of Dnaja3-interacting proteins identified the alpha-subunit of DNA polymerase gamma (Polga) as a client protein. These findings suggest that Dnaja3 is crucial for mitochondrial biogenesis, at least in part, through its chaperone activity on Polga and provide genetic evidence of the necessity for mitochondrial Hsp40 in preventing DCM.

Kinome siRNA screen identifies SMG-1 as a negative regulator of hypoxia-inducible factor-1alpha in hypoxia.

Hypoxia-inducible factor-1 (HIF-1) plays a central role in tumor progression by regulating genes involved in proliferation, glycolysis, angiogenesis, and metastasis. To improve our understanding of HIF-1 regulation by kinome, we screened a kinase-specific small interference RNA library using a hypoxia-response element (HRE) luciferase reporter assay under hypoxic conditions. This screen determined that depletion of cellular SMG-1 kinase most significantly modified cellular HIF-1 activity in hypoxia. SMG-1 is the newest and least studied member of the phosphoinositide 3-kinase-related kinase family, which consists of ATM, ATR, DNA-PKcs, mTOR, and SMG-1. We individually depleted members of the phosphoinositide 3-kinase-related kinase family, and only SMG-1 deficiency significantly augmented HIF-1 activity in hypoxia. We subsequently discovered that SMG-1 kinase activity was activated by hypoxia, and depletion of SMG-1 up-regulated MAPK activity under low oxygen. Suppressing cellular MAPK by silencing ERK1/2 or by treatment with U0126, a MAPK inhibitor, partially blocked the escalation of HIF-1 activity resulting from SMG-1 deficiency in hypoxic cells. Increased expression of SMG-1 but not kinase-dead SMG-1 effectively inhibited the activity of HIF-1alpha. In addition, cellular SMG-1 deficiency increased secretion of the HIF-1alpha-regulated angiogenic factor, vascular epidermal growth factor, and survival factor, carbonic anhydrase IX (CA9), as well as promoted the hypoxic cell motility. Taken together, we discovered that SMG-1 negatively regulated HIF-1alpha activity in hypoxia, in part through blocking MAPK activation.

Verteporfin blocks Clusterin which is required for survival of gastric cancer stem cell by modulating HSP90 function.

Gastric cancer stem cell (GCSC) is implicated in gastric cancer relapse, metastasis and drug resistance. However, the key molecule(s) involved in GCSC survival and the targeting drugs are poorly understood. We discovered increased secreted clusterin (S-Clu) protein expression during the sphere-forming growth of GCSC via mass spectrometry. Overexpression of clusterin was detected in 69/90 (77%) of primary GC tissues and significantly associated with T stage, lymph node metastasis and TNM stage. Depletion of clusterin (Clu, the full-length intracellular clusterin) led to the declustering of GCSC tumorspheres and apoptosis of GCSC. Subsequently, we found clusterin was in complex with heat shock protein 90 beta (HSP90) and involved in regulating the cellular level of HSP90 client proteins. Furthermore, by screening a collection of drugs/inhibitors, we found that verteporfin (VP), a phototherapy drug, blocked clusterin gene expression, decreased the HSP90 client proteins and caused cell death of GCSC. VP treatment is more effective in eradicating GCSCs than in killing GC cells. Both clusterin silencing or VP treatment deterred tumor growth in human GCSC xenografts. These findings collectively suggest that GC patients can promptly benefit from clusterin-targeted therapy as well as VP treatment in combination with or subsequent to conventional chemotherapy for reducing mortality of GC.

PML Recruits TET2 to Regulate DNA Modification and Cell Proliferation in Response to Chemotherapeutic Agent.

Aberrant DNA methylation plays a critical role in the development and progression of cancer. Failure to demethylate and to consequently reactivate methylation-silenced genes in cancer contributes to chemotherapeutic resistance, yet the regulatory mechanisms of DNA demethylation in response to chemotherapeutic agents remain unclear. Here, we show that promyelocytic leukemia (PML) recruits ten-eleven translocation dioxygenase 2 (TET2) to regulate DNA modification and cell proliferation in response to chemotherapeutic agents. TET2 was required by multiple chemotherapeutic agents (such as doxorubicin) to prmote 5-hydroxymethylcytosine (5hmC) formation. Stable isotope labeling with amino acids in cell culture, followed by immunoprecipitation-mass spectrometry, identified potential binding partners of TET2, of which PML mostly enhanced 5hmC formation. PML physically bound to TET2 via the PML C-terminal domain and recruited TET2 to PML-positive nuclear bodies. This interaction was disrupted by the PML-RARA t(15;17) mutation, which stems from chromosomal translocation between DNA encoding the C-terminal domain of PML and the retinoic acid receptor alpha (RARA) gene. In response to chemotherapeutic drugs, PML recruited TET2, regulated DNA modification, reactivated methylation-silenced genes, and impaired cell proliferation. Knockout of PML abolished doxorubicin-promoted DNA modification. In addition, PML and TET2 levels positively correlated with improved overall survival in patients with head and neck cancer. These findings shed insight into the regulatory mechanisms of DNA modification in response to chemotherapeutic agents.Significance: Promyeloctic leukemia protein recruits TET2, regulating DNA modification and cell proliferation in response to chemotherapeutic agents. Cancer Res; 78(10); 2475-89. ©2018 AACR.

Targeted deletion of BMK1/ERK5 in adult mice perturbs vascular integrity and leads to endothelial failure.

Big mitogen-activated protein kinase 1 (BMK1), also known as ERK5, is a member of the MAPK family. Genetic ablation of BMK1 in mice leads to embryonic lethality, precluding the exploration of pathophysiological roles of BMK1 in adult mice. We generated a BMK1 conditional mutation in mice in which disruption of the BMK1 gene is under the control of the inducible Mx1-Cre transgene. Ablation of BMK1 in adult mice led to lethality within 2-4 weeks after the induction of Cre recombinase. Physiological analysis showed that the blood vessels became abnormally leaky after deletion of the BMK1 gene. Histological analysis revealed that, after BMK1 ablation, hemorrhages occurred in multiple organs in which endothelial cells lining the blood vessels became round, irregularly aligned, and, eventually, apoptotic. In vitro removal of BMK1 protein also led to the death of endothelial cells partially due to the deregulation of transcriptional factor MEF2C, which is a direct substrate of BMK1. Additionally, endothelial-specific BMK1-KO leads to cardiovascular defects identical to that of global BMK1-KO mutants, whereas, surprisingly, mice lacking BMK1 in cardiomyocytes developed to term without any apparent defects. Taken together, the data provide direct genetic evidence that the BMK1 pathway is critical for endothelial function and for maintaining blood vessel integrity.

Tid1, a cochaperone of the heat shock 70 protein and the mammalian counterpart of the Drosophila tumor suppressor l(2)tid, is critical for early embryonic development and cell survival.

Tid1 is the mammalian counterpart of the Drosophila tumor suppressor Tid56 and is also a DnaJ protein containing a conserved J domain through which it interacts with the heat shock protein 70 (Hsp70) family of chaperone proteins. We generated a Tid1 conditional mutation in mice, and the subsequent global removal of the Tid1 protein was achieved by crossing these conditional knockout mice with general deletor mice. No Tid1(-/-) embryos were detected as early as embryonic day 7.5 (E7.5). Nonetheless, Tid1-deficient blastocysts were viable, hatched, formed an inner cell mass and trophectoderm, and implanted (E4.5), suggesting that the homozygous mutant embryos die between E4.5 and E7.5. To assess the function of Tid1 in embryonic cells, mouse embryonic fibroblasts with the homologous Tid1 floxed allele were produced. Tid1 removal in these cells led to massive cell death. The death of Tid1-deficient cells could be rescued by ectopic expression of wild-type Tid1 but not by expression of the Tid1 protein that had a mutated J domain and was thus incapable of binding to Hsp70. We propose that Tid1 is critical for early mammalian development, most likely for its function in sustaining embryonic-cell survival, which requires its association with Hsp70.

Big mitogen-activated protein kinase 1/extracellular signal-regulated kinase 5 signaling pathway is essential for tumor-associated angiogenesis.

Although big mitogen-activated protein kinase 1 (BMK1) has been shown to be critical for embryonic angiogenesis, the role of BMK1 in tumor-associated neovascularization is poorly understood. Exogenous tumors were established in BMK1+/+, BMK1flox/+, or BMK1flox/flox mice carrying the Mx1-Cre transgene. Induced deletion of host BMK1 gene significantly reduced the volumes of B16F10 and LL/2 tumor xenografts in BMK1flox/flox mice by 63% and 72%, respectively. Examining the tumors in these induced BMK1-knockout animals showed a significant decrease in vascular density. Localized reexpression of BMK1 in BMK1-knockout mice by administration of adenovirus encoding BMK1 restored tumor growth and angiogenesis to the levels observed in wild-type mice. These observations were further supported by in vivo Matrigel plug assays in which vascular endothelial growth factor- and basic fibroblast growth factor-induced neovacularization was impaired by removing BMK1. Through screening with the Pepchip microarray, we discovered that in BMK1-knockout endothelial cells, phosphorylation of ribosomal protein S6 (rpS6) at Ser235/236 was mostly abrogated, and this BMK1-dependent phosphorylation required the activity of p90 ribosomal S6 kinase (RSK). Immunofluorescent analysis of tumor vasculature from BMK1-knockout and control animals revealed a strong correlation between the presence of BMK1 and the phosphorylation of rpS6 in tumor-associated endothelial cells of blood vessels. As both RSK and rpS6 are known to be important for cell proliferation and survival, which are critical endothelial cell functions during neovascularization, these findings suggest that the BMK1 pathway is crucial for tumor-associated angiogenesis through its role in the regulation of the RSK-rpS6 signaling module.

Tid1 negatively regulates the migratory potential of cancer cells by inhibiting the production of interleukin-8.

Tid1 is the human homologue of the Drosophila tumor suppressor, Tid56. Reducing the expression of Tid1 in MDA-MB231 breast cancer cells enhanced their migration without affecting their survival or growth rate. From microarray screening, we discovered that after Tid1 depletion, the mRNA level of interleukin-8 (IL-8) was significantly increased in these cancer cells, which consequently increased secretion of IL-8 protein by 3.5-fold. The enhanced migration of these Tid1-knockdown cells was blocked by reducing the IL-8 expression or by adding an IL-8 neutralizing antibody to the culture medium, suggesting that enhancement of cell motility in these Tid1-deficient cells is dependent on the de novo synthesis of IL-8. Subsequently, we found that abrogating the nuclear factor kappaB binding site in the IL-8 promoter completely blocked the Tid1 depletion-induced IL-8 expression in the breast cancer cells. As increased IL-8 levels are known to promote tumor metastasis, we tested the effect of Tid1 knockdown on tumor metastasis and found that Tid1 depletion enhanced the metastasis of breast cancer cells in animals. Together, these results indicate that Tid1 negatively regulates the motility and metastasis of breast cancer cells, most likely through attenuation of nuclear factor kappaB activity on the promoter of the IL8 gene.

Corrigendum: Targeting BMK1 Impairs the Drug Resistance to Combined Inhibition of BRAF and MEK1/2 in Melanoma.

This corrects the article DOI: 10.1038/srep46244.

Targeting BMK1 Impairs the Drug Resistance to Combined Inhibition of BRAF and MEK1/2 in Melanoma.

Combined inhibition of BRAF and MEK1/2 (CIBM) improves therapeutic efficacy of BRAF-mutant melanoma. However, drug resistance to CIBM is inevitable and the drug resistance mechanisms still remain to be elucidated. Here, we show that BMK1 pathway contributes to the drug resistance to CIBM. Considering that ERK1/2 pathway regulates cellular processes by phosphorylating, we first performed a SILAC phosphoproteomic profiling of CIBM. Phosphorylation of 239 proteins was identified to be downregulated, while phosphorylation of 47 proteins was upregulated. Following siRNA screening of 47 upregulated proteins indicated that the knockdown of BMK1 showed the most significant ability to inhibit the proliferation of CIBM resistant cells. It was found that phosphorylation of BMK1 was enhanced in resistant cells, which suggested an association of BMK1 with drug resistance. Further study indicated that phospho-activation of BMK1 by MEK5D enhanced the resistance to CIBM. Conversely, inhibition of BMK1 by shRNAi or BMK1 inhibitor (XMD8-92) impaired not only the acquirement of resistance to CIBM, but also the proliferation of CIBM resistant cells. Further kinome-scale siRNA screening demonstrated that SRC\MEK5 cascade promotes the phospho-activation of BMK1 in response to CIBM. Our study not only provides a global phosphoproteomic view of CIBM in melanoma, but also demonstrates that inhibition of BMK1 has therapeutic potential for the treatment of melanoma.

Insulin-like growth factor-1 enhances inflammatory responses in endothelial cells: role of Gab1 and MEKK3 in TNF-alpha-induced c-Jun and NF-kappaB activation and adhesion molecule expression.

Insulin-like growth factor (IGF)-1 and the type I IGF-1 receptor are important regulators of vascular function that may contribute to cardiovascular disease. We hypothesized that IGF-1 causes endothelial cell dysfunction and expression of neutrophil and monocyte adhesion molecules by enhancing pro-inflammatory cytokine signal transduction. Long-term IGF-1 treatment of endothelial cells potentiated c-Jun and nuclear factor NF-kappaB activation by tumor necrosis factor (TNF)-alpha and enhanced TNF-alpha-mediated adhesion molecule expression. In response to IGF-1 treatment, the expression of kinases in the c-Jun/c-Jun NH(2)-terminal kinase signaling pathway (MEKK1, MEK4, and JNK1/2) was unchanged, but expressions of insulin receptor substrate-1 and Grb2-associated binder-1 (Gab1) were significantly decreased. Because Gab1 is involved in both c-Jun and NF-kappaB activation by TNF-alpha, we focused on Gab1-dependent signaling. Gab1 inhibited c-Jun and NF-kappaB transcriptional activation by TNF-alpha. Interestingly, Gab1 inhibited c-Jun transcriptional activity induced by MEKK3 but not MEKK1 and MEK4. Gab1 associated with MEKK3, and a catalytically inactive form of MEKK3 inhibited TNF-alpha-induced c-Jun and NF-kappaB transcriptional activation, suggesting a critical role for Gab1 and MEKK3 in TNF-alpha signaling. These data demonstrate that Gab1 and MEKK3 play important roles in endothelial cell inflammation via regulating the activation of c-Jun and NF-kappaB. Furthermore, the IGF-1-mediated downregulation of Gab1 expression represents a novel mechanism to promote vascular inflammation and atherosclerosis.

Tid1, the human homologue of a Drosophila tumor suppressor, reduces the malignant activity of ErbB-2 in carcinoma cells.

The ErbB-2/HER-2 receptor tyrosine kinase is overexpressed in a wide range of solid human tumors. The ErbB-2 gene product is a transmembrane glycoprotein belonging to the epidermal growth factor receptor family, and its cytoplasmic domain is responsible for sending the mitogenic signals into cells. We discovered that this domain of ErbB-2 interacts with Tid1 protein, the human counterpart of the Drosophila tumor suppressor Tid56, whose null mutation causes lethal tumorigenesis during the larval stage. Tid1 also is known as a cochaperone of heat shock protein 70 (HSP70) and binds to HSP70 through its conserved DnaJ domain. We found that increased expression of Tid1 in human mammary carcinomas overexpressing ErbB-2 suppresses the expression level of ErbB-2 and attenuates the resultant ErbB-2-dependent oncogenic extracellular signal-regulated kinase 1/2 and big mitogen-activated protein kinase 1 signaling pathways leading to programmed cell death (PCD). A functional DnaJ domain of Tid1 also is required for its inhibition of ErbB-2 expression and the consequent PCD of carcinoma cells resulting from increased Tid1 expression. Importantly, ErbB-2-dependent tumor progression in animals is inhibited by increased expression of Tid1 in tumor cells. Collectively, these results suggest that Tid1 modulates the uncontrolled proliferation of ErbB-2-overexpressing carcinoma cells by reducing ErbB-2 expression and as a result suppresses the ErbB-2-dependent cancerous signaling and tumor progression. Moreover, the cochaperonic and regulatory functions of Tid1 on HSP70 most likely play an essential role in this antitumor function of Tid1 in carcinoma cells.

Role of the BMK1/ERK5 signaling pathway: lessons from knockout mice.

Mitogen-activated protein (MAP) kinase cascades play a central role in mediating extracellular stimuli-induced intracellular signaling during cell activation. The fourth and least studied mammalian MAP kinase pathway, big MAP kinase 1 (BMK1), also known as extracellular signal regulated kinase 5 (ERK5), is activated in response to growth factors and stress. Activation of this signaling pathway has been implicated not only in physiological functions such as cell survival, proliferation and differentiation but also in pathological processes such as carcinogenesis, cardiac hypertrophy and atherosclerosis. In recent years a series of gene-targeted mice lacking components within the BMK1 cascade have been generated, which have enabled us to investigate the role of the BMK1 pathway within different tissues. Analyses of these knockout mice have led to major discoveries in the role of BMK1 signaling in angiogenesis and in cardiac development. Moreover, studies using conditional BMK1 knockout mice, which circumvent the early embryonic lethality of BMK1 knockouts, have unveiled the importance of BMK1 in endothelial survival and maintenance of vascular integrity during adulthood. Here we summarize current understanding of the function of BMK1, as well as include new data generated from a series of tissue-specific BMK1 knockout mice in an attempt to dissect the role of the BMK1 pathway in various cell types in animals.

Activation of mitogen-activated protein kinases and p90 ribosomal S6 kinase in failing human hearts with dilated cardiomyopathy.

OBJECTIVE: A new member of the MAP kinase family, big MAP kinase-1 (BMK1), has been recently identified to promote cell growth and attenuate apoptosis. P90 ribosomal S6 kinase (p90RSK), one of the potentially important substrates of extracellular signal regulated kinase (ERK), regulates gene expression in part via phosphorylation of CREB and the Na(+)/H(+) exchanger. Recently, we have demonstrated that the activity of BMK1, Src (the upstream regulator of BMK1) and p90RSK was increased in hypertrophied myocardium induced by pressure-overload in the guinea pig. However, the abundance and activity of these kinases in human hearts are unknown. METHODS: In addition to the three classical MAP kinases (ERK, p38 kinase, and c-Jun NH(2)-terminal kinase (JNK)), we examined the protein expression and activity of Src, BMK1, and p90RSK in explanted hearts from patients with dilated cardiomyopathy (n=9). Normal donor hearts, which were not suitable for transplant for technical reasons, were used as controls (n=5). RESULTS: There were no significant differences in the levels of protein expression of these kinases between normal and failing hearts. ERK1/2 and p90RSK were activated in heart failure compared to control (P<0.01 and P<0.03, respectively), while the activity of p38 kinase was decreased (P<0.05) and the activity of JNK was unchanged in heart failure. By contrast, the activities of Src and BMK1 were significantly reduced in end-stage heart failure compared to normal donor hearts (P<0.05). CONCLUSION: These data suggest that multiple MAP kinases, p90RSK, and Src are differentially regulated in human failing myocardium of patients with idiopathic dilated cardiomyopathy and may be involved in the pathogenesis of this complex disease.

Inhibition of BMK1 pathway suppresses cancer stem cells through BNIP3 and BNIP3L.

Cancer stem cells (CSCs) possess many characteristics associated with stem cells and are believed to drive tumor initiation. Although targeting of CSCs offers great promise for the new generation of therapeutics, lack of the effective drugable target and appropriate pharmacological reagents significantly impedes the development of chemotherapies. Here, we show that the phosphorylation of BMK1 was significantly correlated with not only embryonic and induced pluripotent stem (iPS) cells, but also the CSCs. It was showed that activation of BMK1 by the expression of MEK5D enhanced the self-renew (sphere formation), proliferation (clone formation) and tumorigenic capacity of CSCs. While BMK1 inhibitor, XMD8-92, suppressed these capacities. RNA-seq and microarray analysis revealed that inhibition of BMK1 significantly enhanced the expression of BNIP3 and BNIP3L, which play important roles in cell death. Further study indicated that shRNA-mediated knock down of BNIP3 and BNIP3L impairs the BMK1 inhibitor, XMD8-92-induced suppression of sphere formation and clone formation of CSC. Collectively, these results not only indicate that BMK1 plays an important role in maintaining "stemness" of CSCs, but also implicate that BMK1 might be a potential drug target for CSCs.

Activation of big MAP kinase 1 (BMK1/ERK5) inhibits cardiac injury after myocardial ischemia and reperfusion.

Big MAP kinase 1 (BMK1/ERK5) plays a critical role in pre-natal development of the cardiovascular system and post-natal eccentric hypertrophy of the heart. Of the two isoforms upstream of MAPK-kinase 5 (MEK5) known to exist, only the longer MEK5alpha isoform potently activates BMK1. We generated cardiac-specific constitutively active form of the MEK5alpha (CA-MEK5alpha transgenic (Tg) mice), and observed a 3 to 4-fold increase in endogenous BMK1 activation and hyperphosphorylation of connexin 43 in the ventricles of the Tg compared to wild-type mice. The CA-MEK5alpha-Tg-mice demonstrated a profoundly accelerated recovery of left ventricular developed pressure after ischemia/reperfusion. We propose a novel role for BMK1 in protecting the heart from ischemia/reperfusion-induced cardiac injury.

Structural determinants for ERK5 (MAPK7) and leucine rich repeat kinase 2 activities of benzo[e]pyrimido-[5,4-b]diazepine-6(11H)-ones.

The benzo[e]pyrimido-[5,4-b]diazepine-6(11H)-one core was discovered as a novel ERK5 (also known as MAPK7 and BMK1) inhibitor scaffold, previously. Further structure-activity relationship studies of this scaffold led to the discovery of ERK5-IN-1 (26) as the most selective and potent ERK5 inhibitor reported to date. 26 potently inhibits ERK5 biochemically with an IC50 of 0.162 ± 0.006 µM and in cells with a cellular EC50 for inhibiting epidermal growth factor induced ERK5 autophosphorylation of 0.09 ± 0.03 µM. Furthermore, 26 displays excellent selectivity over other kinases with a KINOMEscan selectivity score (S10) of 0.007, and exhibits exceptional bioavailability (F%) of 90% in mice. 26 will serve as a valuable tool compound to investigate the ERK5 signaling pathway and as a starting point for developing an ERK5 directed therapeutic agent.

BMK1 kinase suppresses epithelial-mesenchymal transition through the Akt/GSK3ß signaling pathway.

Epithelial-mesenchymal transition (EMT) plays a crucial role in the development of cancer metastasis. The mitogen-activated protein (MAP) kinases extracellular signal-regulated kinase, c-jun-NH(2)-kinase, and p38 have been implicated in promoting EMT, but a role for the MAP kinase BMK1 has not been studied. Here, we report that BMK1 signaling suppresses EMT. BMK1 elevation augmented E-cadherin-mediated cell-cell adhesion, downregulated mesenchymal markers, and decreased cell motility. Conversely, BMK1 silencing attenuated E-cadherin-mediated cell-cell adhesion, upregulated mesenchymal markers, and stimulated cell motility. BMK1 depletion dramatically increased the accumulation of endogenous Snail in the nuclear compartment. Snail accumulation was mediated by Akt/GSK3ß signaling, which was activated by a modulation in the expression of the mTOR inhibitor DEPTOR. In support of these observations, BMK1 depletion promoted metastasis in vivo. Together, our findings reveal a novel mechanism of EMT control via mTOR/Akt inhibition that suppresses cancer metastasis.

Forced expression of miR-143 represses ERK5/c-Myc and p68/p72 signaling in concert with miR-145 in gut tumors of Apc(Min) mice.

Recently, miR-143 and miR-145 have been shown to belong to a subset of microRNAs whose expression is controlled by a complex of a tumor suppressor p53 and DEAD-box RNA helicase subunits p68/p72. While accumulating studies have acknowledged that both miRNAs function as tumor suppressors and are similarly regulated, evidence of their coordinated action against tumorigenesis has been poorly presented. Herein, we establish transgenic mice that express miR-143 under the control of the CAG regulatory unit. When crossbred with Apc(Min/+) mice, the development of tumors in the small intestines is significantly attenuated. In the transgenic small intestine tumors, the endogenous miR-145 is also enhanced and the expression of c-Myc and p68/p72, both of which have been reported to be pivotal for gut tumor development, is suppressed, corresponding to the downregulation of ERK5. We demonstrate that the combination of miR-143 and miR-145 inhibits the expression of c-Myc in human colon cancer cells, whereas miR-145 retards that of p72. Moreover, we show the possibilities that miR-145 modulates p72 expression through its 3' untranslated region and that c-Myc downregulation is involved in both p68 suppression and miR-145 induction. These findings suggest that forced expression of miR-143, probably interacting with endogenous miR-145, inhibits ERK5/c-Myc and p68/p72/ß-catenin signaling and hampers small intestine tumor development in Apc(Min/+) mice. This unique cascade, in turn, may prevent overproduction of a subset of tumor suppressive miRNAs by repressing their own modulators, p68/p72.