Genomic structure, alternative splicing and tissue expression of rFrp/sFRP-4, the rat frizzled related protein gene

Secreted frizzled related proteins (sFRP) are regulators of Wnt signaling pathways that play central roles in developmental processes and oncogenesis. Various sFRP genes have been cloned from different tissues and implicated in diverse biological activities. rFrp, the rat homologue of sFRP-4, was initially identified as being upregulated in mutant p53-induced cellular transformation. Here, we report on the isolation of five novel splice variants, rFrp/sFRP-4 II, II, III, IVa and IVb. The complete rFrp/sFRP-4 genomic structure spans over 31 kb covering 9 exons. Except for the variant IVb, which was derived from IVa by alternative polyadenylation signal, variants I to IVa were alternatively spliced to different exons in the 3'end of mRNA and resulted in transcripts with truncated open reading frame. The deduced proteins of the variants had truncated C-termini, however, the two key functional protein domains, the cysteine-rich domain and the netrin-like domain of the isoforms, were not altered. In addition, different transcriptional initiation sites were found with variants II and IV, implying that these variants may be regulated differently from the rFrp/sFRP-4. RT-PCR analysis showed that these splice variants displayed different patterns of tissue-specific expression. Northern blot analysis revealed that the rFrp/sFRP-4 is most abundant in the ovary. Taken together, our findings suggest that alternative splicing of rFrp/sFRP-4 plays a role in regulating tissue-specific expression. The truncated C terminals of rFrp/sFRP-4 variants may confer structural specificity and hence exert different biological functions in different tissues. Characterization of these novel splice variants should help to elucidate the function of the sFRP family gene. © 2005 Elsevier B.V. All rights reserved.postprin

Novel RhoGAP independent pathway of tumor suppressor DLC1 regulates cancer invasion and metastasis

This journal suppl. entitled: Proceedings: AACR Annual Meeting 2014; April 5-9, 2014 ...Molecular and Cellular Biology - Poster Presentations - Proffered Abstracts - Poster Presentations - Tumor Suppressors 2: abstract no. 1565Hepatocellular carcinoma (HCC) is the fifth most common cancer worldwide. Deleted in Liver Cancer 1 (DLC1) is a tumor suppressor gene critically involved in hepatocarcinogenesis. DLC1 is a Rho GTPase activating protein (RhoGAP), which serves as the negative regulator of Rho proteins. Rho proteins are important in remodeling of actin cytoskeleton, transcription regulation, cell proliferation, tumorigenesis and metastasis. Apart from RhoGAP activity, the inhibitory activity of DLC1 is also dependent on its proper focal adhesion localization. It has been found that tensin proteins are responsible for directing DLC1 to the focal adhesions via their interaction which is important to the tumor suppression activity of DLC1. Recently, we identified that ...postprin

Identification and characterization of EBP, a novel EEN binding protein that inhibits Ras signaling and is recruited into the nucleus by the MLL-EEN fusion protein

The chimeric MLL-EEN fusion protein is created as a result of chromosomal translocation t(11;19)(q23;p13). EEN, an Src homology 3 (SH3) domain-containing protein in the endophilin family, has been implicated in endocytosis, although little is known about its role in leukemogenesis mediated by the MLL-EEN fusion protein. In this study, we have identified and characterized EBP, a novel EEN binding protein that interacts with the SH3 domain of EEN through a proline-rich motif PPERP. EBP is a ubiquitous protein that is normally expressed in the cytoplasm but is recruited to the nucleus by MLL-EEN with a punctate localization pattern characteristic of the MLL chimeric proteins. EBP interacts simultaneously with EEN and Sos, a guanine-nucleotide exchange factor for Ras. Coexpressoin of EBP with EEN leads to suppression of Ras-induced cellular transformation and Ras-mediated activation of Elk-1. Taken together, our findings suggest a new mechanism for MLL-EEN-mediated leukemogenesis in which MLL-EEN interferes with the Ras-suppressing activities of EBP through direct interaction. © 2004 by The American Society of Hematology.postprin

DLC1 (deleted in liver cancer 1)

Review on DLC1 (deleted in liver cancer 1), with data on DNA, on the protein encoded, and where the gene is implicated

Epigenetic silencing of microRNA-199b-5p is associated with acquired chemoresistance via activation of JAG1-Notch1 signaling in ovarian cancer.

Epithelial ovarian cancer is a highly lethal and aggressive gynecological malignancy. The high mortality rate is due in part to the fact that many advanced cancer patients become refractory to current chemotherapeutic agents, leading to tumor recurrence and death. However, the underlying mechanisms leading to chemoresistance remain obscure. Here, we report that the loss of miR-199b-5p due to progressive epigenetic silencing leads to the activation of the JAG1-mediated Notch1 signaling cascade, thereby leading to the development of acquired chemoresistance in ovarian cancer. Using miRCURY LNATM microRNA array and Q-PCR analyses of two pairs of cisplatin-sensitive and -resistant ovarian cancer cell lines, we identified miR-199b-5p as significantly down-regulated in cisplatin-resistant ovarian cancer cells and confirmed that miR-199b-5p is clinically associated with advanced and poor survival ovarian cancers. Interestingly, the loss of miR-199b-5p could be restored by 5-Aza-dC-mediated demethylation, and methylated specific PCR (MS-PCR), bisulfite-sequencing and pyrosequencing revealed that the promoter region of miR-199b-5p was hypermethylated. Computational and mechanistic analyses identified JAG1 as a primary target of miR-199b-5p. Notably, the reduced expression of miR-199b-5p was found to be inversely correlated with the increased expression of JAG1 using an ovarian cancer tissue array. Enforced expression of miR-199b-5p sensitized ovarian cancer cells to cisplatin-induced cytotoxicity both in vitro and in vivo. Conversely, re-expression of miR-199b-5p and siRNA-mediated JAG1 knockdown or treatment with Notch specific inhibitor γ-secretase (GSI) attenuated JAG1-Notch1 signaling activity, thereby enhancing cisplatin-mediated cell cytotoxicity. Taken together, our study suggests that the epigenetic silencing of miR-199b-5p during tumor progression is significantly associated with acquired chemoresistance in ovarian cancer through the activation of JAG1-Notch1 signaling.published_or_final_versio

Rho GTPase-activating protein deleted in liver cancer suppresses cell proliferation and invasion in hepatocellular carcinoma

Deleted in liver cancer (DLC1) is a candidate tumor suppressor gene recently isolated from human hepatocellular carcinoma. Structurally, DLC1 protein contains a conserved GTPase-activating protein for Rho family protein (RhoGAP) domain, which has been thought to regulate the activity of Rho family proteins. Previous studies indicated that DLC1 was frequently inactivated in cancer cells. In the present study, we aimed to characterize the tumor suppressor roles of DLC1 in hepatocellular carcinoma. We showed that DLC1 significantly inhibited cell proliferation, anchorage-independent growth, and in vivo tumorigenicity when stably expressed in hepatocellular carcinoma cells. Moreover, DLC1 expression greatly reduced the motility and invasiveness of hepatocellular carcinoma cells. With RhoGAP-deficient DLC1 mutant (DLC1-K714E), we showed that the RhoGAP activity was essential for DLC1-mediated tumor suppressor function. Furthermore, the 292- to 648-amino acid region and the steroidogenic acute regulatory related lipid transfer domain played an auxiliary role to RhoGAP and tumor suppressor function of DLC1. Taken together, our findings showed that DLC1 functions as a tumor suppressor in hepatocellular carcinoma and provide the first evidence to support the hypothesis that DLC1 suppresses cancer cell growth by negatively regulating the activity of Rho proteins. ©2005 American Association for Cancer Research.postprin

Elevated TAK1 augments tumor growth and metastatic capacities of ovarian cancer cells through activation of NF-κB signaling

Transforming growth factor (TGF)-β-activating kinase 1 (TAK1) is a serine/threonine kinase which is frequently associated with human cancer progression. However, its functional role in tumorigenesis is still controversial. Here, we report that TAK1 enhances the oncogenic capacity of ovarian cancer cells through the activation of NF-κB signaling. We found that TAK1 is frequently upregulated and significantly associated with high-grade and metastatic ovarian cancers. Mechanistic studies showed that Ser412 phosphorylation is required for TAK1 in activating NF-κB signaling and promotes aggressiveness of ovarian cancer cells. Conversely, suppression of TAK1 activity by point mutation at Ser412, RNAi mediated gene knockdown or TAK1 specific inhibitor ((5Z) -7-Oxozeaenol) remarkably impairs tumor growth and metastasis in ovarian cancer in vitro and in vivo. Our study underscores the importance of targeting TAK1 as a promising therapeutic approach to counteract the ovarian cancer progression.published_or_final_versio

Elevated TAK1 augments tumor growth and metastatic capacities of ovarian cancer cells through activation of NF-κB signaling

Transforming growth factor (TGF)-β-activating kinase 1 (TAK1) is a serine/threonine kinase which is frequently associated with human cancer progression. However, its functional role in tumorigenesis is still controversial. Here, we report that TAK1 enhances the oncogenic capacity of ovarian cancer cells through the activation of NF-κB signaling. We found that TAK1 is frequently upregulated and significantly associated with high-grade and metastatic ovarian cancers. Mechanistic studies showed that Ser412 phosphorylation is required for TAK1 in activating NF-κB signaling and promotes aggressiveness of ovarian cancer cells. Conversely, suppression of TAK1 activity by point mutation at Ser412, RNAi mediated gene knockdown or TAK1 specific inhibitor ((5Z) -7-Oxozeaenol) remarkably impairs tumor growth and metastasis in ovarian cancer in vitro and in vivo. Our study underscores the importance of targeting TAK1 as a promising therapeutic approach to counteract the ovarian cancer progression.published_or_final_versio

ANXA3/JNK Signaling Promotes Self-Renewal and Tumor Growth, and Its Blockade Provides a Therapeutic Target for Hepatocellular Carcinoma

Frequent tumor relapse in hepatocellular carcinoma (HCC) has been commonly attributed to the presence of residual cancer stem cells (CSCs) after conventional treatments. We have previously identified and characterized CD133 to mark a specific CSC subset in HCC. In the present study, we found endogenous and secretory annexin A3 (ANXA3) to play pivotal roles in promoting cancer and stem cell-like features in CD133+ liver CSCs through a dysregulated JNK pathway. Blockade of ANXA3 with an anti-ANXA3 monoclonal antibody in vitro as well as in human HCC xenograft models resulted in a significant reduction in tumor growth and self-renewal. Clinically, ANXA3 expression in HCC patient sera closely associated with aggressive clinical features. Our results suggest that ANXA3 can serve as a novel diagnostic biomarker and that the inhibition of ANXA3 may be a viable therapeutic option for the treatment of CD133+ liver-CSC-driven HCC. © 2015 The Authors.published_or_final_versio