Krüppel-like factor 5 promotes apoptosis triggered by tumor necrosis factor α in LNCaP prostate cancer cells via up-regulation of mitogen-activated protein kinase kinase 7

Targeting SphK1/2 by SKI-178 inhibits prostate cancer cell growth

Sphingosine kinases (SphK), including SphK1 and SphK2, are important enzymes promoting progression of prostate cancer. SKI-178 is a novel and highly potent SphK1/2 dual inhibitor. We here tested the potential anti-prostate cancer cell activity of SKI-178. Bioinformatics analyses and results from local tissues demonstrated that that both SphK1 and SphK2 are upregulated in human prostate cancer tissues. Ectopic overexpression of SphK1 and SphK2, by lentiviral constructs, promoted primary prostate cancer cell proliferation and migration. In primary human prostate cancer cells and immortalized cell lines, SKI-178 potently inhibited cell viability, proliferation, cell cycle progression and cell migration, causing robust cell death and apoptosis. SKI-178 impaired mitochondrial functions, causing mitochondrial depolarization, reactive oxygen species production and ATP depletion.SKI-178 potently inhibited SphK activity and induced ceramide production, without affecting SphK1/2 expression in prostate cancer cells. Further, SKI-178 inhibited Akt-mTOR activation and induced JNK activation in prostate cancer cells. Contrarily, a constitutively-active Akt1 construct or the pharmacological JNK inhibitors attenuated SKI-178-induced cytotoxicity in prostate cancer cells. In vivo, daily intraperitoneal injection of a single dose of SKI-178 potently inhibited PC-3 xenograft growth in nude mice. SphK inhibition, ceramide production, ATP depletion and lipid peroxidation as well as Akt-mTOR inactivation and JNK activation were detected in PC-3 xenograft tissues with SKI-178 administration. Together, targeting SphK1/2 by SKI-178 potently inhibited prostate cancer cell growth in vitro and in vivo.

The roles and regulation of the KLF5 transcription factor in cancers

Krüppel‐like factor 5 (KLF5) is a member of the KLF family. Recent studies have suggested that KLF5 regulates the expression of a large number of new target genes and participates in diverse cellular functions, such as stemness, proliferation, apoptosis, autophagy, and migration. In response to multiple signaling pathways, various transcriptional modulation and posttranslational modifications affect the expression level and activity of KLF5. Several transgenic mouse models have revealed the physiological and pathological functions of KLF5 in different cancers. Studies of KLF5 will provide prognostic biomarkers, therapeutic targets, and potential drugs for cancers.

Astragaloside-IV regulates endoplasmic reticulum stress-mediated neuronal apoptosis in a murine model of Parkinson's disease via the lincRNA-p21/CHOP pathway

OBJECTIVES

Astragaloside-IV (AS-IV) protects the nerve cells of Parkinson's disease (PD) from damage. Long non-coding RNA (lincRNA) has been found to be important for many diseases. Lincnra-p21 is abnormally expressed in PD. The purpose of this study was to investigate whether Astragaloside-IV (AS-IV) affects endoplasmic reticulum stress (ERS)-induced neuronal apoptosis in PD, and its possible mechanisms.

METHODS

The PD mouse model was established via injecting 1-methyl-4-phenyl-1, 2, 3, 6- tetrahydropyridine (MPTP) and the PD cell model was established via inducing the MN9D cell line with 1-methyl-4-pehnyl-pyridine (MPP⁺). The behavioral testing of PD model mice was tested after AS-IV treatment and PD-related lincRNAs expression were detected by qRT-PCR. After treatment of PD model cells with AS-IV, lincRNA-p21 expression was detected by qRT-PCR, and cell viability and apoptosis were detected by MTT assay and flow cytometry, respectively. The binding of lincRNA-p21 to C/EBP-homologous (CHOP) protein was investigated by RNA immunoprecipitation and RNA pull-down, and the effect of lincRNA-p21 on the ubiquitination of CHOP protein was examined by ubiquitination assay. The role of lincRNA-p21 in PD model was studied by cell transfection.

RESULTS

In PD mice, AS-IV can improve the behavior of mice and significantly inhibit expression of lincRNA-p21. Similarly, AS-IV can obviously restrain the expression of lincRNA-p21 in PD cells, and obviously elevated cell viability and restrained apoptosis. LincRNA-p21 is able to bind to CHOP protein. Further studies showed that restraint of lincRNA-p21 expression can facilitate ubiquitination of CHOP and accelerate its protein degradation. In AS-IV-treated PD model cells, overexpression of lincRNA-p21 lessened cell viability and facilitated apoptosis, whereas low expression of CHOP reversed this result.

CONCLUSION

In this study, we found that AS-IV can lessen the expression of CHOP protein by restraining the expression of lincRNA-p21 in the PD model, thereby inhibiting neuronal apoptosis.

The long non-coding RNA TUG1-miR-9a-5p axis contributes to ischemic injuries by promoting cardiomyocyte apoptosis via targeting KLF5

Non-coding RNAs participate in many cardiac pathophysiological processes, including myocardial infarction (MI). Here we showed the interplay between long non-coding RNA taurine-upregulated gene 1 (lncR-TUG1), miR-9a-5p (miR-9) and Krüppel-like factor 5 (KLF5). LncR-TUG1 was upregulated in ischemic heart and in cultured cardiomyocytes exposed to H₂O₂. Knockdown of lncR-TUG1 markedly ameliorated impaired cardiac function of MI mice. Further study showed that lncR-TUG1 acted as a competitive endogenous RNA of miR-9, and silencing of lncR-TUG1 inhibited cardiomyocyte apoptosis by upregulating miR-9 expression. Furthermore, the miR-9 overexpression obviously prevented ischemia injury and significantly inhibited H₂O₂-induced cardiomyocyte apoptosis via inhibition of mitochondrial apoptotic pathway. KLF5, as a target gene of miR-9 by dual-luciferase reporter assay, was involved in the process of miR-9 in regulating cardiomyocyte apoptosis. Our data identified the KLF5 was downregulated by miR-9 overexpression and knockdown of KLF5 inhibited cardiomyocyte apoptosis induced by H₂O₂. MiR-9 exerts anti-cardiomyocyte apoptotic affects by targeting KLF5. Collectively, our data identify a novel function of lncR-TUG1/miR-9/KLF5 axis in regulating cardiomyocyte apoptosis that affects myocardial infarction progression.

MKK7 transcription positively or negatively regulated by SP1 and KLF5 depends on HDAC4 activity in glioma

JNK activity has been implicated in the malignant proliferation, invasion and drug-resistance of glioma cells (GCs), but the molecular mechanisms underlying JNK activation are currently unknown. Here, we reported that MKK7, not MKK4, directly activates JNK in GCs and exerts oncogenic effects on tumor formation. Notably, MKK7 expression in glioma tissues was closely correlated with the grade of the glioma and JNK/c-Jun activation. Mechanistically, MKK7 transcription critically depends on the complexes formed by HDAC4 and the transcriptional factors SP1 and Krüppel-like factor-5 (KLF5), wherein HDAC4 directly deacetylates both SP1 and KLF5 and synergistically upregulates MKK7 transcription through two SP1 sites located on its promoter. In contrast, the increases in acetylated-SP1 and acetylated-KLF5 after HDAC4 inhibition switched to transcriptionally suppress MKK7. Selective inhibition of HDAC4 by LMK235, siRNAs or blockage of SP1 and KLF5 by the ectopic dominant-negative SP1 greatly reduced the malignant capacity of GCs. Furthermore, suppression of both MKK7 expression and JNK/c-Jun activities was involved in the tumor-growth inhibitory effects induced by LMK235 in U87-xenograft mice. Interestingly, HDAC4 is highly expressed in glioma tissues, and the rate of HDAC4 nuclear import is closely correlated with glioma grade, as well as with MKK7 expression. Collectively, these findings demonstrated that highly expressed MKK7 contributes to JNK/c-Jun signaling-mediated glioma formation. MKK7 transcription, regulated by SP1 and KLF5, critically depends on HDAC4 activity, and inhibition of HDAC4 presents a potential strategy for suppressing the oncogenic roles of MKK7/JNK/c-Jun signaling in GCs.

KLF5 promotes apoptosis induced by phorbol ester as an effector of the autocrine factor TNFα in LNCaP prostate cancer cells

Krüppel-like factor 5 (KLF5) is frequently deleted and inactivated in prostate cancer, and exerts tumor-suppressing function in prostate cancer cells. However, the function of KLF5 in the apoptosis of prostate cancer cells remains unclear. In the present study, the effect of KLF5 on phorbol 12-myristate 13-acetate (PMA)-induced apoptosis was investigated in prostate cancer LNCaP cells. It was demonstrated that PMA induced the expression of KLF5 at the mRNA and protein level. To identify whether KLF5 regulates the activity of the downstream pathway, stable KLF5 knockdown or overexpression cell lines were constructed with lentivirus harboring shRNA targeting KLF5 or full-length KLF5 in LNCaP cells. Knockdown of KLF5 significantly decreased PMA-induced apoptosis, while cell apoptosis was significantly increased following KLF5 overexpression compared with the corresponding control groups. Consistently, expression of cleaved poly(ADP-ribose) polymerase and caspase-3 induced by PMA was decreased following KLF5 knockdown and increased following KLF5 overexpression. Using the control medium from cells treated with PMA, it was demonstrated that KLF5 is required for the control medium to induce apoptosis. c-Jun N-terminal kinase (JNK) activity is essential for the apoptosis induced by PMA. It was revealed that knockdown of KLF5 decreased, while overexpression of KLF5 increased the phosphorylation of JNK induced by PMA and control medium treatment. Furthermore, inhibition of tumor necrosis factor α (TNFα) decreased KLF5 expression and significantly decreased cell apoptosis induced by PMA, and control medium. This data indicates that KLF5 is essential for the apoptosis induced by PMA in LNCaP prostate cancer cells. Furthermore, KLF5 is essential for activity of the autocrine factor TNFα, which is secreted by cells treated with PMA and mediates the function of PMA-induced apoptosis through regulating the activity of JNK signaling pathway. These results provide novel insights into the complexity of the signaling pathways regulating apoptosis in prostate cancer cells, which could aid in the development of novel treatments for patients with prostate cancer.