p27 suppresses cyclooxygenase-2 expression by inhibiting p38β and p38δ-mediated CREB phosphorylation upon arsenite exposure

Downregulation of miR-200c stabilizes XIAP mRNA and contributes to invasion and lung metastasis of bladder cancer

Our previous studies have demonstrated that XIAP promotes bladder cancer metastasis through upregulating RhoGDIβ/MMP-2 pathway. However, the molecular mechanisms leading to the XIAP upregulation was unclear. In current studies, we found that XIAP was overexpressed in human high grade BCs, high metastatic human BCs, and in mouse invasive BCs. Mechanistic studies indicated that XIAP overexpression in the highly metastatic T24T cells was due to increased mRNA stability of XIAP that was mediated by downregulated miR-200c. Moreover, the downregulated miR-200c was due to CREB inactivation, while miR-200c downregulation reduced its binding to the 3’-UTR region of XIAP mRNA. Collectively, our results demonstrate the molecular basis leading to XIAP overexpression and its crucial role in BC invasion.

Transcriptional and post-transcriptional upregulation of p27 mediates growth inhibition of isorhapontigenin (ISO) on human bladder cancer cells

There are few approved drugs available for the treatment of muscle-invasive bladder cancer (MIBC). Recently, we have demonstrated that isorhapontigenin (ISO), a new derivative isolated from the Chinese herb Gnetum cleistostachyum, effectively induces cell-cycle arrest at the G0/G1 phase and inhibits anchorage-independent cell growth through the miR-137/Sp1/cyclin D1 axis in human MIBC cells. Herein, we found that treatment of bladder cancer (BC) cells with ISO resulted in a significant upregulation of p27, which was also observed in ISO-treated mouse BCs that were induced by N-butyl-N-(4-hydroxybutyl) nitrosamine (BBN). Importantly, knockdown of p27 caused a decline in the ISO-induced G0-G1 growth arrest and reversed ISO suppression of anchorage-independent growth in BC cells. Mechanistic studies revealed that ISO promoted p27 expression at mRNA transcription level through increasing direct binding of forkhead box class O1 (FOXO1) to its promoter, while knockdown of FOXO1 attenuated ISO inhibition of BC cell growth. On the other hand, ISO upregulated the 3'-untranslated region (3'-UTR) activity of p27, which was accompanied by a reduction of miR-182 expression. In line with these observations, ectopic expression of miR-182 significantly blocked p27 3'-UTR activity, whereas mutation of the miR-182-binding site at p27 mRNA 3'-UTR effectively reversed this inhibition. Accordingly, ectopic expression of miR-182 also attenuated ISO upregulation of p27 expression and impaired ISO inhibition of BC cell growth. Our results not only provide novel insight into understanding of the underlying mechanism related to regulation of MIBC cell growth but also identify new roles and mechanisms underlying ISO inhibition of BC cell growth.

XIAP RING domain mediates miR-4295 expression and subsequently inhibiting p63α protein translation and promoting transformation of bladder epithelial cells

The X-linked inhibitor of apoptosis protein (XIAP) contains three N-terminal BIR domains that mediate anti-apoptosis and one C-terminal RING finger domain whose function(s) are not fully defined. Here we show that the RING domain of XIAP strongly inhibits the expression of p63α, a known tumor suppressor. XIAP knockdown in urothelial cells or RING deletion in knockin mice markedly upregulates p63α expression. This RING-mediated p63α downregulation is critical for the malignant transformation of normal urothelial cells following EGF treatment. We further show that the RING domain promotes Sp1-mediated transcription of miR-4295 which targets the 3′UTR of p63α mRNA and consequently inhibits p63α translation. Our results reveal a previously unknown function of the RING of XIAP in promoting miR-4295 transcription, thereby reducing p63α translation and enhancing urothelial transformation. Our data offer novel insights into the multifunctional effects of the XIAP RING domain on urothelial tumorigenesis and the potential for targeting this frequently overexpressed protein as a therapeutic alternative.

NF-κB p65 Overexpression Promotes Bladder Cancer Cell Migration via FBW7-Mediated Degradation of RhoGDIα Protein

BACKGROUND

Since invasive bladder cancer (BC) is one of the most lethal urological malignant tumors worldwide, understanding the molecular mechanisms that trigger the migration, invasion, and metastasis of BC has great significance in reducing the mortality of this disease. Although RelA/p65, a member of the NF-kappa B transcription factor family, has been reported to be upregulated in human BCs, its regulation of BC motility and mechanisms have not been explored yet.

METHODS

NF-κBp65 expression was evaluated in N-butyl-N-(4-hydroxybutyl)-nitrosamine (BBN)-induced high invasive BCs by immunohistochemistry staining and in human BC cell lines demonstrated by Western Blot. The effects of NF-κBp65 knockdown on BC cell migration and invasion, as well as its regulated RhoGDIα and FBW7, were also evaluated in T24T cells by using loss- and gain-function approaches. Moreover, the interaction of FBW7 with RhoGDIα was determined with immunoprecipitation assay, while critical role of ubiquitination of RhoGDIα by FBW7 was also demonstrated in the studies.

RESULTS

p65 protein was remarkably upregulated in the BBN-induced high invasive BCs and in human BC cell lines. We also observed that p65 overexpression promoted BC cell migration by inhibiting RhoGDIα expression. The regulatory effect of p65 on RhoGDIα expression is mediated by its upregulation of FBW7, which specifically interacted with RhoGDIα and promoted RhoGDIα ubiquitination and degradation. Mechanistic studies revealed that p65 stabilizing the E3 ligase FBW7 protein was mediated by its attenuating pten mRNA transcription.

CONCLUSIONS

We demonstrate that p65 overexpression inhibits pten mRNA transcription, which stabilizes the protein expression of ubiquitin E3 ligase FBW7, in turn increasing the ubiquitination and degradation of RhoGDIα protein and finally promoting human BC migration. The novel identification of p65/PTEN/FBW7/RhoGDIα axis provides a significant insight into understanding the nature of BC migration, further offering a new theoretical support for cancer therapy.

Role of STAT3 and FOXO1 in the Divergent Therapeutic Responses of Non-metastatic and Metastatic Bladder Cancer Cells to miR-145

Although miR-145 is the most frequently downregulated miRNA in bladder cancer, its exact stage association and downstream effector have not been defined. Here, we found that miR-145 was upregulated in human patients with bladder cancer with lymph node metastasis and in metastatic T24T cell line. Forced expression of miR-145 promoted anchorage-independent growth of T24T cells accompanied by the downregulation of forkhead box class O1 (FOXO1). In contrast, in non-metastatic T24 cells, miR-145 overexpression inhibited cell growth with upregulation of FOXO1, and the knockdown of FOXO1 abolished the miR-145-mediated inhibition of cell growth. Mechanistic studies revealed that miR-145 directly bound to and attenuated 3'-untranslated region (UTR) activity of foxo1 mRNA in both T24 and T24T cells. Interestingly, miR-145 suppressed STAT3 phosphorylation at Tyr705 and increased foxo1 promoter transcriptional activity in T24 cells, but not in T24T cells, suggesting a role of STAT3 in the divergent responses to miR-145. Supporting this was our finding that STAT3 knockdown mimicked miR-145-mediated upregulation of FOXO1 in T24T cells and inhibition of anchorage-independent growth. Consistently, ectopic expression of miR-145 promoted tumor formation of xenograft T24T cells, whereas such promoting effect became inhibitory due to specific knockdown of STAT3. Together, our findings demonstrate the stage-specific association and function of miR-145 in bladder cancers and provide novel insights into the therapeutic targeting of miR-145. Mol Cancer Ther; 16(5); 924-35. ©2017 AACR.

p38β Mitogen-Activated Protein Kinase Signaling Mediates Exenatide-Stimulated Microglial β-Endorphin Expression

Recent discoveries established that activation of glucagon-like peptide-1 receptors (GLP-1Rs) mediates neuroprotection and antinociception through microglial β-endorphin expression. This study aimed to explore the underlying signaling mechanisms of microglial β-endorphin. GLP-1Rs and β-endorphin were coexpressed in primary cultures of microglia. Treatment with the GLP-1R agonist exenatide concentration-dependently stimulated microglial expression of the β-endorphin precursor gene proopiomelanocortin (POMC) and peptides, with EC₅₀ values of 4.1 and 7.5 nM, respectively. Exenatide also significantly increased intracellular cAMP levels and expression of p-protein kinase A (PKA), p-p38, and p-cAMP response element binding protein (CREB) in cultured primary microglia. Furthermore, exenatide-induced microglial expression of POMC was completely blocked by reagents that specifically inhibit adenylyl cyclase and activation of PKA, p38, and CREB. In addition, knockdown of p38β (but not p38α) using short interfering RNA (siRNA) eliminated exenatide-induced microglial p38 phosphorylation and POMC expression. In contrast, lipopolysaccharide increased microglial activation of p38, and knockdown of p38α (but not p38β) partially suppressed expression of proinflammatory factors (including tumor necrosis factor-α, interleukin-1β, and interleukin-6). Exenatide-induced phosphorylation of p38 and CREB was also totally blocked by the PKA inhibitor and siRNA/p38β, but not by siRNA/p38α Seven-day intrathecal injections of siRNA/p38β (but not siRNA/p38α) completely blocked exenatide-induced spinal p38 activation, β-endorphin expression, and mechanical antiallodynia in rats with established neuropathy, although siRNA/p38β and siRNA/p38α were not antiallodynic. To our knowledge, our results are the first to show a causal relationship between the PKA-dependent p38β mitogen-activated protein kinase/CREB signal cascade and GLP-1R agonism-mediated microglial β-endorphin expression. The differential role of p38α and p38β activation in inflammation and nociception was also highlighted.

Upregulation of SQSTM1/p62 contributes to nickel-induced malignant transformation of human bronchial epithelial cells

Chronic lung inflammation is accepted as being associated with the development of lung cancer caused by nickel exposure. Therefore, identifying the molecular mechanisms that lead to a nickel-induced sustained inflammatory microenvironment that causes transformation of human bronchial epithelial cells is of high significance. In the current studies, we identified SQSTM1/p62 as a novel nickel-upregulated protein that is important for nickel-induced inflammatory TNF expression, subsequently resulting in transformation of human bronchial epithelial cells. We found that nickel exposure induced SQSTM1 protein upregulation in human lung epithelial cells in vitro and in mouse lung tissues in vivo. The SQSTM1 upregulation was also observed in human lung squamous cell carcinoma. Further studies revealed that the knockdown of SQSTM1 expression dramatically inhibited transformation of human lung epithelial cells upon chronic nickel exposure, whereas ectopic expression of SQSTM1 promoted such transformation. Mechanistic studies showed that the SQSTM1 upregulation by nickel was the compromised result of upregulating SQSTM1 mRNA transcription and promoting SQSTM1 protein degradation. We demonstrated that nickel-initiated SQSTM1 protein degradation is mediated by macroautophagy/autophagy via an MTOR-ULK1-BECN1 axis, whereas RELA is important for SQSTM1 transcriptional upregulation following nickel exposure. Furthermore, SQSTM1 upregulation exhibited its promotion of nickel-induced cell transformation through exerting an impetus for nickel-induced inflammatory TNF mRNA stability. Consistently, the MTOR-ULK1-BECN1 autophagic cascade acted as an inhibitory effect on nickel-induced TNF expression and cell transformation. Collectively, our results demonstrate a novel SQSTM1 regulatory network that promotes a nickel-induced tumorigenic effect in human bronchial epithelial cells, which is negatively controlled by an autophagic cascade following nickel exposure.

SESN2/sestrin 2 induction-mediated autophagy and inhibitory effect of isorhapontigenin (ISO) on human bladder cancers

Isorhapontigenin (ISO) is a new derivative of stilbene isolated from the Chinese herb Gnetum cleistostachyum. Our recent studies have revealed that ISO treatment at doses ranging from 20 to 80 μM triggers apoptosis in multiple human cancer cell lines. In the present study, we evaluated the potential effect of ISO on autophagy induction. We found that ISO treatment at sublethal doses induced autophagy effectively in human bladder cancer cells, which contributed to the inhibition of anchorage-independent growth of cancer cells. In addition, our studies revealed that ISO-mediated autophagy induction occurred in a SESN2 (sestrin 2)-dependent and BECN1 (Beclin 1, autophagy related)-independent manner. Furthermore, we identified that ISO treatment induced SESN2 expression via a MAPK8/JNK1 (mitogen-activated protein kinase 8)/JUN-dependent mechanism, in which ISO triggered MAPK8-dependent JUN activation and facilitated the binding of JUN to a consensus AP-1 binding site in the SESN2 promoter region, thereby led to a significant transcriptional induction of SESN2. Importantly, we found that SESN2 expression was dramatically downregulated or even lost in human bladder cancer tissues as compared to their paired adjacent normal tissues. Collectively, our results demonstrate that ISO treatment induces autophagy and inhibits bladder cancer growth through MAPK8-JUN-dependent transcriptional induction of SESN2, which provides a novel mechanistic insight into understanding the inhibitory effect of ISO on bladder cancers and suggests that ISO might act as a promising preventive and/or therapeutic drug against human bladder cancer.

Role of PTEN-Akt-CREB Signaling Pathway in Nervous System impairment of Rats with Chronic Arsenite Exposure

The nervous system is a target of arsenic toxicity. Phosphatase and tensin homologue deleted on chromosome 10/protein kinase B/cAMP-response element binding protein (PTEN/Akt/CREB) signaling pathway has been reported to be involved in maintaining normal function of the nervous system, modulating growth and proliferation of neurocyte, regulating neuron synaptic plasticity, and long-term memory. And many studies have demonstrated that expressions of PTEN, Akt, and CREB protein were influenced by arsenic, but it is not clear whether this signaling pathway is involved in the nervous system impairment of rats induced by chronic arsenite exposure, and we have addressed this in this study. Eighty male Sprague-Dawley (SD) rats were randomly divided into eight groups (n = 10 each), four groups exposed to NaAsO2 (0, 5, 10, and 50 mg/L NaAsO2 in drinking water) for 3 months, the other four groups exposed to NaAsO2 (0, 5, 10, 50 mg/L NaAsO2 in drinking water) for 6 months. Hematoxylin and eosin (HE) staining showed that chronic arsenite exposure induced varying degrees of damage in cerebral neurons. And arsenite exposure increased arsenic amount in serum and brain samples in a dose- and time-dependent manner. Moreover, the protein levels of PTEN and Akt in brain tissue were not significantly changed compared with the control group, but p-Akt, CREB, and p-CREB were all significantly downregulated in arsenite-exposed groups with a dose-dependent pattern. These results suggested that chronic arsenite exposure negatively regulated the PTEN-Akt-CREB signaling pathway, and dysfunction of the signaling pathway might be one of the mechanisms of nervous system impairment induced by chronic arsenite exposure.

NF-κB1 inhibits c-Myc protein degradation through suppression of FBW7 expression

NF-κB is a well-known transcription factor in regulation of multiple gene transcription and biological processes, and most of them are relied on its transcriptional activity of the p65/RelA subunit, while biological function of another ubiquitously expressed subunit NF-κB1 (p50) remains largely unknown due to lack transcriptional activation domain. Here we discovered a novel biological function of p50 as a regulator of oncogenic c-Myc protein degradation upon arsenite treatment in a NF-κB transcriptional-independent mechanism. Our results found that p50 was crucial for c-Myc protein induction following arsenite treatment by using specific knockdown and deletion of p50 in its normal expressed cells as well as reconstituting expression of p50 in its deficient cells. Subsequently we showed that p50 upregulated c-Myc protein expression mainly through inhibiting its degradation. We also identified that p50 exhibited this novel property by suppression of FBW7 expression. FBW7 was profoundly upregulated in p50-defecient cells in comparison to that in p50 intact cells, whereas knockdown of FBW7 in p50-/- cells restored arsenite-induced c-Myc protein accumulation, assuring that FBW7 up-regulation was responsible for defect of c-Myc protein expression in p50-/- cells. In addition, we discovered that p50 suppressed fbw7 gene transcription via inhibiting transcription factor E2F1 transactivation. Collectively, our studies demonstrated a novel function of p50 as a regulator of c-Myc protein degradation, contributing to our notion that p50-regulated protein expression through multiple levels at protein translation and degradation, further providing a significant insight into the understanding of biomedical significance of p50 protein.

Inflammatory cytokine COX-2 mediated cell proliferation through increasing cyclin D1 expression induced by inorganic arsenic in SV-HUC-1 human uroepithelial cells

Inorganic arsenic promotes SV-HUC-1 cells proliferation.

Loss of p27 upregulates MnSOD in a STAT3-dependent manner, disrupts intracellular redox activity and enhances cell migration

Cell migration is a dynamic process that is central to a variety of physiological functions as well as disease pathogenesis. The modulation of cell migration by p27 (officially known as CDKN1B) has been reported, but the exact mechanism(s) whereby p27 interacts with downstream effectors that control cell migration have not been elucidated. By systematically comparing p27(+/+) mouse embryonic fibroblasts (MEFs) with genetically ablated p27(-/-) MEFs using wound-healing, transwell and time-lapse microscopic analyses, we provide direct evidence that p27 inhibits both directional and random cell migration. Identical results were obtained with normal and cancer epithelial cells using complementary knockdown and overexpression approaches. Additional studies revealed that overexpression of manganese superoxide dismutase (MnSOD, officially known as SOD2) and reduced intracellular oxidation played a key role in increased cell migration in p27-deficient cells. Furthermore, we identified signal transducer and activator of transcription 3 (STAT3) as the transcription factor responsible for p27-regulated MnSOD expression, which was further mediated by ERK- and ATF1-dependent transactivation of the cAMP response element (CRE) within the Stat3 promoter. Collectively, our data strongly indicate that p27 plays a crucial negative role in cell migration by inhibiting MnSOD expression in a STAT3-dependent manner.