The Smad7-Skp2 complex orchestrates Myc stability, impacting on the cytostatic effect of TGF-ß.

In most human cancers the Myc proto-oncogene is highly activated. Dysregulation of Myc oncoprotein contributes to tumorigenesis in numerous tissues and organs. Thus, targeting Myc stability could be a crucial step for cancer therapy. Here we report Smad7 as a key molecule regulating Myc stability and activity by recruiting the F-box protein, Skp2. Ectopic expression of Smad7 downregulated the protein level of Myc without affecting the transcription level, and significantly repressed its transcriptional activity, leading to inhibition of cell proliferation and tumorigenic activity. Furthermore, Smad7 enhanced ubiquitylation of Myc through direct interaction with Myc and recruitment of Skp2. Ablation of Smad7 resulted in less sensitivity to the growth inhibitory effect of TGF-ß by inducing stable Myc expression. In conclusion, these findings that Smad7 functions in Myc oncoprotein degradation and enhances the cytostatic effect of TGF-ß signaling provide a possible new therapeutic approach for cancer treatment.

Homozygous deletions at 3p22, 5p14, 6q15, and 9p21 result in aberrant expression of tumor suppressor genes in gastric cancer.

Homozygous deletion is a frequent mutational mechanism of silencing tumor suppressor genes in cancer. Therefore, homozygous deletions have been analyzed for identification of tumor suppressor genes that can be utilized as biomarkers or therapeutic targets for cancer treatment. In this study, to elucidate potential tumor suppressor genes involved in gastric cancer (GC), we analyzed the entire set of large homozygous deletions in six human GC cell lines through genome- and transcriptome-wide approaches. We identified 51 genes in homozygous deletion regions of chromosomes and confirmed the deletion frequency in tumor tissues of 219 GC patients from The Cancer Genome Atlas database. We evaluated the effect of homozygous deletions on the mRNA level and found significantly affected genes in chromosome bands 9p21, 3p22, 5p14, and 6q15. Among the genes in 9p21, we investigated the potential tumor suppressive effect of KLHL9. We demonstrated that ectopic expression of KLHL9 inhibited cell proliferation and tumor formation in KLHL9-deficient SNU-16 cell line. In addition, we observed that homozygous focal deletions generated truncated transcripts of TGFBR2, CTNNA1, and STXBP5. Ectopic expression of two kinds of TGFBR2-reverse GADL1 fusion genes suppressed TGF-ß signaling, which may lead to the loss of sensitivity to TGF-ß tumor suppressive activity. In conclusion, our findings suggest that novel tumor suppressor genes that are aberrantly expressed through homozygous deletions may play important roles in gastric tumorigenesis.

N-linked glycosylation is essential for anti-tumor activities of KIAA1324 in gastric cancer.

KIAA1324 is a transmembrane protein largely reported as a tumor suppressor and favorable prognosis marker in various cancers, including gastric cancer. In this study, we report the role of N-linked glycosylation in KIAA1324 as a functional post-translational modification (PTM). Loss of N-linked glycosylation eliminated the potential of KIAA1324 to suppress cancer cell proliferation and migration. Furthermore, we demonstrated that KIAA1324 undergoes fucosylation, a modification of the N-glycan mediated by fucosyltransferase, and inhibition of fucosylation also significantly suppressed KIAA1324-induced cell growth inhibition and apoptosis of gastric cancer cells. In addition, KIAA1324-mediated apoptosis and tumor regression were inhibited by the loss of N-linked glycosylation. RNA sequencing (RNAseq) analysis revealed that genes most relevant to the apoptosis and cell cycle arrest pathways were modulated by KIAA1324 with the N-linked glycosylation, and Gene Regulatory Network (GRN) analysis suggested novel targets of KIAA1324 for anti-tumor effects in the transcription level. The N-linked glycosylation blockade decreased protein stability through rapid proteasomal degradation. The non-glycosylated mutant also showed altered localization and lost apoptotic activity that inhibits the interaction between GRP78 and caspase 7. These data demonstrate that N-linked glycosylation of KIAA1324 is essential for the suppressive role of KIAA1324 protein in gastric cancer progression and indicates that KIAA1324 may have anti-tumor effects by targeting cancer-related genes with N-linked glycosylation. In conclusion, our study suggests the PTM of KIAA1324 including N-linked glycosylation and fucosylation is a necessary factor to consider for cancer prognosis and therapy improvement.

Effects of estradiol on HIF-1α expression and trophoblast differentiation in first trimester villous explant cultures.

OBJECTIVE: The purpose of this study was to investigate the effects of estradiol on the expression of hypoxia-inducible factor (HIF)-1α and the differentiation of trophoblasts in human first trimester villous explant cultures. METHODS: Villous explant cultures were established from first trimester human placentas (6-8 weeks of gestation, n=3). Normal villous tissues were explanted on Matrigel and incubated under 3% O2 tension for 5 days. To evaluate the effects of estradiol on the villous explant cultures, 1 ng/mL of estradiol was added to the culture medium. The morphological integrities and viabilities of the villous explants were monitored. Immunohistochemistry for α5 and α1 integrin was performed to assess differentiation of extravillous trophoblasts (EVTs). Expression of HIF-1α in villous explant cultures was evaluated by western blotting and densitometry. RESULTS: EVTs emerging from first trimester villous explant cultures formed outgrowths of cells from the distal ends and invaded the surrounding Matrigel. Exposure of villous explants to estradiol resulted in the decreased outgrowth of cells from the distal end and decreased expression of α5 integrin. However, estradiol treatment increased the invasion of villous explants into the surrounding Matrigel, concomitant with the increased expression of α1 integrin, indicating differentiation of EVTs into more invasive EVTs. On western blots, the expression of HIF-1α decreased significantly after treatment with estradiol under 3% O2 tension. CONCLUSION: Our findings suggest that estradiol may downregulate expression of HIF-1α in placenta, which in turn promote trophoblast differentiation into invasive phenotype.

KIAA1324 Suppresses Gastric Cancer Progression by Inhibiting the Oncoprotein GRP78.

Recent advances in genome and transcriptome analysis have contributed to the identification of many potential cancer-related genes. Furthermore, biological and clinical investigations of the candidate genes provide us with a better understanding of carcinogenesis and development of cancer treatment. Here, we report a novel role of KIAA1324 as a tumor suppressor in gastric cancer. We observed that KIAA1324 was downregulated in most gastric cancers from transcriptome sequencing data and found that histone deacetylase was involved in the suppression of KIAA1324. Low KIAA1324 levels were associated with poor prognosis in gastric cancer patients. In the xenograft model, KIAA1324 significantly reduced tumor formation of gastric cancer cells and decreased development of preformed tumors. KIAA1324 also suppressed proliferation, invasion, and drug resistance and induced apoptosis in gastric cancer cells. Through protein interaction analysis, we identified GRP78 (glucose-regulated protein 78 kDa) as a KIAA1324-binding partner. KIAA1324 blocked oncogenic activities of GRP78 by inhibiting GRP78-caspase-7 interaction and suppressing GRP78-mediated AKT activation, thereby inducing apoptosis. In conclusion, our study reveals a tumor suppressive role of KIAA1324 via inhibition of GRP78 oncoprotein activities and provides new insight into the diagnosis and treatment of gastric cancer.

TRAF6 mediates IL-1ß/LPS-induced suppression of TGF-ß signaling through its interaction with the type III TGF-ß receptor.

Transforming growth factor-ß1 (TGF-ß1) is an important anti-inflammatory cytokine that modulates and resolves inflammatory responses. Recent studies have demonstrated that inflammation enhances neoplastic risk and potentiates tumor progression. In the evolution of cancer, pro-inflammatory cytokines such as IL-1ß must overcome the anti-inflammatory effects of TGF-ß to boost pro-inflammatory responses in epithelial cells. Here we show that IL-1ß or Lipopolysaccharide (LPS) suppresses TGF-ß-induced anti-inflammatory signaling in a NF-κB-independent manner. TRAF6, a key molecule in IL-1ß signaling, mediates this suppressive effect through interaction with the type III TGF-ß receptor (TßRIII), which is TGF-ß-dependent and requires type I TGF-ß receptor (TßRI) kinase activity. TßRI phosphorylates TßRIII at residue S829, which promotes the TRAF6/TßRIII interaction and consequent sequestration of TßRIII from the TßRII/TßRI complex. Our data indicate that IL-1ß enhances the pro-inflammatory response by suppressing TGF-ß signaling through TRAF6-mediated sequestration of TßRIII, which may be an important contributor to the early stages of tumor progression.