Xiaofeng Ding

A miR-200b/200c/429-Binding Site Polymorphism in the 3′ Untranslated Region of the AP-2α Gene Is Associated with Cisplatin Resistance

The transcription factor AP-2α functions as a tumor suppressor by regulating various genes that are involved in cell proliferation and apoptosis. Chemotherapeutic drugs including cisplatin induce post-transcriptionally endogenous AP-2α, which contributes to chemosensitivity by enhancing therapy-induced apoptosis. microRNAs (miRNAs) miR-200b, miR-200c and miR-429 (miR-200b/200c/429) are up-regulated in endometrial and esophageal cancers, and their overexpression correlates with resistance to cisplatin treatment. Using computational programs, we predicted that the 3′ untranslated region (UTR) of AP-2α gene contains a potential miRNA response element (MRE) for the miR-200b/200c/429 family, and the single nucleotide polymorphism (SNP) site rs1045385 (A or C allele) resided within the predicted MRE. Luciferase assays and Western blot analysis demonstrated that the miR-200b/200c/429 family recognized the MRE in the 3′ UTR of AP-2α gene and negatively regulated the expression of endogenous AP-2α proteins. SNP rs1045385 A>C variation enhanced AP-2α expression by disrupting the binding of the miR-200b/200c/429 family to the 3′ UTR of AP-2α. The effects of the two polymorphic variants on cisplatin sensitivity were determined by clonogenic assay. The overexpression of AP-2α with mutant 3′ UTR (C allele) in the endometrial cancer cell line HEC-1A, which has high levels of endogenous miR-200b/200c/429 and low levels of AP-2α protein, significantly increased cisplatin sensitivity, but overexpression of A allele of AP-2α has no significant effects, compared with mock transfection. We concluded that miR-200b/200c/429 induced cisplatin resistance by repressing AP-2α expression in endometrial cancer cells. The SNP (rs1045385) A>C variation decreased the binding of miR-200b/200c/429 to the 3′ UTR of AP-2α, which upregulated AP-2α protein expression and increased cisplatin sensitivity. Our results suggest that SNP (rs1045385) may be a potential prognostic marker for cisplatin treatment.

MicroRNA-373 is upregulated and targets TNFAIP1 in human gastric cancer, contributing to tumorigenesis.

The role of microRNAs (miRNAs) in regulating gene expression is currently an area of intense interest. Previous studies have shown that miRNA-372 plays crucial roles in gastric tumorigenesis by targeting the mRNA of tumor necrosis factor, α-induced protein 1 (TNFAIP1). The present study showed that miR-373 is upregulated in gastric adenocarcinoma tissue and gastric carcinoma cell lines when compared to normal gastric tissues. The overexpression of miR-373 in the gastric cancer cells increased cell proliferation. A bioinformatics search revealed a conserved target site within the 3′ untranslated region (UTR) of TNFAIP1, an immediate-early response gene of the endothelium induced by TNF-α. The overexpression of miR-373 caused the suppression of a luciferase reporter containing the TNFAIP1 3′UTR in the HEK293 cells and reduced the levels of TNFAIP1 protein in the AGS cells. The mRNA levels of TNFAIP1 in the gastric cancer and normal gastric tissues were negatively correlated with the expression levels of miR-373 in these tissues. Moreover, the knockdown of TNFAIP1 had a similar effect to the overexpression of miR-373. The overexpression of TNFAIP1 may partly rescue the inhibition of proliferation caused by the inhibitor, miR-373-ASO. Taken together, these findings demonstrate an oncogenic role for miR-373, similar to that of miR-372, in controlling cell growth through the downregulation of TNFAIP1.

KCTD1 Suppresses Canonical Wnt Signaling Pathway by Enhancing β-catenin Degradation

The canonical Wnt signaling pathway controls normal embryonic development, cellular proliferation and growth, and its aberrant activity results in human carcinogenesis. The core component in regulation of this pathway is β-catenin, but molecular regulation mechanisms of β-catenin stability are not completely known. Here, our recent studies have shown that KCTD1 strongly inhibits TCF/LEF reporter activity. Moreover, KCTD1 interacted with β-catenin both in vivo by co-immunoprecipitation as well as in vitro through GST pull-down assays. We further mapped the interaction regions to the 1-9 armadillo repeats of β-catenin and the BTB domain of KCTD1, especially Position Ala-30 and His-33. Immunofluorescence analysis indicated that KCTD1 promotes the cytoplasmic accumulation of β-catenin. Furthermore, protein stability assays revealed that KCTD1 enhances the ubiquitination/degradation of β-catenin in a concentration-dependent manner in HeLa cells. And the degradation of β-catenin mediated by KCTD1 was alleviated by the proteasome inhibitor, MG132. In addition, KCTD1-mediated β-catenin degradation was dependent on casein kinase 1 (CK1)- and glycogen synthase kinase-3β (GSK-3β)-mediated phosphorylation and enhanced by the E3 ubiquitin ligase β-transducin repeat-containing protein (β-TrCP). Moreover, KCTD1 suppressed the expression of endogenous Wnt downstream genes and transcription factor AP-2α. Finally, we found that Wnt pathway member APC and tumor suppressor p53 influence KCTD1-mediated downregulation of β-catenin. These results suggest that KCTD1 functions as a novel inhibitor of Wnt signaling pathway.

Transcription factor AP-2α regulates acute myeloid leukemia cell proliferation by influencing Hoxa gene expression

Transcription factor AP-2α mediates transcription of a number of genes implicated in mammalian development, cell proliferation and carcinogenesis. In the current study, we identified Hoxa7, Hoxa9 and Hox cofactor Meis1 as AP-2α target genes, which are involved in myeloid leukemogenesis. Luciferase reporter assays revealed that overexpression of AP-2α activated transcription activities of Hoxa7, Hoxa9 and Meis1, whereas siRNA of AP-2α inhibited their transcription activities. We found that AP-2 binding sites in regulatory regions of three genes activated their transcription by mutant analysis and AP-2α could interact with AP-2 binding sites in vivo by chromatin immunoprecipitation (ChIP). Further results showed that the AP-2α shRNA efficiently inhibited mRNA and protein levels of Hoxa7, Hoxa9 and Meis1 in AML cell lines U937 and HL60. Moreover, decreased expression of AP-2α resulted in a significant reduction in the growth and proliferation of AML cells in vitro. Remarkably, AP-2α knockdown leukemia cells exhibit decreased tumorigenicity in vivo compared with controls. Finally, AP-2α and target genes in clinical acute myeloid leukemia samples of M5b subtype revealed variable expression levels and broadly paralleled expression. These data support a role of AP-2α in mediating the expression of Hoxa genes in acute myeloid leukemia to influence the proliferation and cell survival.

LIM domain protein TES changes its conformational states in different cellular compartments

The human TESTIN (TES) is a putative tumor suppressor and localizes to the cytoplasm as a component of focal adhesions and cell contacts. TES contains a PET domain in the NH2-terminus and three tandem LIM domains in the COOH-terminus. It has been hypothesized that interactions between two termini of TES might lead to a “closed” conformational state of the protein. Here, we provide evidence for different conformational states of TES. We confirmed that the NH2-terminus of TES can interact with its third LIM domain in the COOH-terminus by GST pull-down assays. In addition, antisera against the full-length or two truncations of TES were prepared to examine the relationship between the conformation and cellular distribution of the protein. We found that these antisera recognize different regions of TES and showed that TES is co-localised with the marker protein B23 in nucleolus, in addition to its localization in endoplasmic reticulum (ER). Furthermore, our co-immunoprecipitation (co-IP) analysis of TES and B23 demonstrated their co-existence in the same complex. Taken together, our results suggest that TES has different conformational states in different cellular compartments, and a “closed” conformational state of TES may be involved in nucleolar localization.

Identification and characterization of the novel protein CCDC106 that interacts with p53 and promotes its degradation

MINT‐7681212: p53 (uniprotkb:P04637) and CCDC106 (uniprotkb:Q9BWC9) colocalise (MI:0403) by fluorescence microscopy (MI:0416)

Direct regulation of caspase‑3 by the transcription factor AP‑2α is involved in aspirin‑induced apoptosis in MDA‑MB‑453 breast cancer cells

Aspirin has been reported to trigger apoptosis in various cancer cell lines. However, the detailed mechanisms involved remain elusive. The present study aimed to investigate whether aspirin plays a role in apoptosis of MDA-MB-453 cells. The effect of aspirin on the proliferation of human MDA-MB-453 cells breast cancer cells was evaluated using MTT assay, flow cytometry and western blotting. The present study reports that aspirin induces the apoptosis of MDA‑MB‑453 breast cancer cells which was attributed to the increased expression and activation of caspase‑3. Moreover, AP‑2α, a transcription factor highly expressed in MDA‑MB‑453 cells, was identified as a negative regulator of caspase‑3 transcription and AP‑2α was attenuated following aspirin treatment. Therefore, aspirin may increase the expression of caspase‑3 by inducing the degradation of AP‑2α, which increases activated caspase‑3 expression, thereby triggering apoptosis in MDA‑MB‑453 cells. Thus, aspirin may be used in breast cancer therapy.

TNFAIP1 interacts with KCTD10 to promote the degradation of KCTD10 proteins and inhibit the transcriptional activities of NF-κB and AP-1

The broad-complex, tramtrack, and bric-a-brac/poxvirus and zinc finger domain-containing protein tumor necrosis factor, alpha-induced protein 1 (TNFAIP1) was first identified as a gene whose expression can be induced by the tumor necrosis factor alpha. Some studies showed that TNFAIP1 may function in DNA replication, apoptosis and human diseases. However, the definite functions and the mechanisms of TNFAIP1 are poorly known. In this study, we performed a yeast two-hybrid assay and used TNFAIP1 as the bait to screen human brain cDNA library. Potassium channel tetramerisation domain containing 10 (KCTD10) was identified as TNFAIP1-interacting partner. The KCTD10–TNFAIP1 interaction was then confirmed by the in vitro GST pull-down assays and the in vivo co-immunoprecipitation and colocalization assays. In addition, protein degradation and ubiquitin assays revealed TNFAIP1 overexpression resulted in ubiquitin-mediated degradation of KCTD10 proteins, which was significantly alleviated with the proteasome inhibitor MG132 treatment. Furthermore, transient transfection assays with two reporters showed that TNFAIP1 and KCTD10 inhibited the transcriptional activities of nuclear factor kappa B (NF-κB) and activating protein-1 reporters. Taken together, our results indicated the novel interaction and function between KCTD10 and TNFAIP1 in human PDIP1 family.

AP-2α inhibits hepatocellular carcinoma cell growth and migration

Transcription factor AP-2α is involved in many types of human cancers, but its role in hepatocellular carcinogenesis is largely unknown. In this study, we found that expression of AP-2α was low in 40% of human hepatocellular cancers compared with adjacent normal tissues by immunohistochemical analysis. Moreover, AP-2α expression was low or absent in hepatocellular cancer cell lines (HepG2, Hep3B, SMMC-7721 and MHHC 97-H). Human liver cancer cell lines SMMC-7721 and Hep3B stably overexpressing AP-2α were established by lentiviral infection and puromycin screening, and the ectopic expression of AP-2α was able to inhibit hepatocellular cancer cell growth and proliferation by cell viability, MTT assay and liquid colony formation in vitro and in vivo. Furthermore, AP-2α overexpression decreased liver cancer cell migration and invasion as assessed by wound healing and Transwell assays, increasing the sensitivity of liver cancer cells to cisplatin analyzed by MTT assays. Also AP-2α overexpression suppressed the sphere formation and renewed the ability of cancer stem cells. Finally, we found that AP-2α is epigenetically modified and modulates the levels of phosphorylated extracellular signal-regulated protein kinase (ERK), β-catenin, p53, EMT, and CD133 expression in liver cancer cell lines. These results suggested that AP-2α expression is low in human hepatocellular cancers by regulating multiple signaling to affect hepatocellular cancer cell growth and migration. Therefore, AP-2α might represent a novel potential target in human hepatocellular cancer therapy.

Human intersectin 2 (ITSN2) binds to Eps8 protein and enhances its degradation.

Participates in actin remodeling through Rac and receptor endocytosis via Rab5. Here, we used yeast two-hybrid system with Eps8 as bait to screen a human brain cDNA library. ITSN2 was identified as the novel binding factor of Eps8. The interaction between ITSN2 and Eps8 was demonstrated by the in vivo co-immunoprecipitation and colocalization assays and the in vitro GST pull-down assays. Furthermore, we mapped the interaction domains to the region between amino acids 260-306 of Eps8 and the coiled-coil domain of ITSN2. In addition, protein stability assays and immunofluorescence analysis showed ITSN2 overexpression induced the degradation of Eps8 proteins, which was markedly alleviated with the lysosome inhibitor NH4Cl treatment. Taken together, our results suggested ITSN2 interacts with Eps8 and stimulates the degradation of Eps8 proteins.