Identification and characterization of FHL3 as a novel angiogenin-binding partner

The Roles of FHL3 in Cancer

The four and a half LIM domain protein 3, also named the LIM-protein FHL3, belongs to the LIM-only family. Based on the special structure of LIM-only proteins, FHL3 can perform significant functions in muscle proliferation and cardiovascular diseases by regulating cell growth and signal transduction. In recent years, there has been increasing evidence of a relation between FHLs and tumor biology, since FHL3 is often overexpressed or downregulated in different cancers. On the one hand, FHL3 can function as a tumor suppressor and influence the expression of downstream genes. On the other hand, FHL3 can also play a role as an oncoprotein in some cancers to promote tumor progression via phosphorylation. Thus, FHL3 is proposed to have a dual effect on cancer progression, reflecting its complex roles in cancer. This review focuses on the roles of FHL3 in cancer progression and discusses the interaction of FHL3 with other proteins and transcription factors. Finally, the clinical significance of FHL3 for the treatment of cancers is discussed.

Selectively Suppressing Tumor Angiogenesis for Targeted Breast Cancer Therapy by Genetically Engineered Phage

Antiangiogenesis is a promising approach to cancer therapy but is limited by the lack of tumor-homing capability of the current antiangiogenic agents. Angiogenin, a protein overexpressed and secreted by tumors to trigger angiogenesis for their growth, has never been explored as an antiangiogenic target in cancer therapy. Here it is shown that filamentous fd phage, as a biomolecular biocompatible nanofiber, can be engineered to become capable of first homing to orthotopic breast tumors and then capturing angiogenin to prevent tumor angiogenesis, resulting in targeted cancer therapy without side effects. The phage is genetically engineered to display many copies of an identified angiogenin-binding peptide on its side wall and multiple copies of a breast-tumor-homing peptide at its tip. Since the tumor-homing peptide can be discovered and customized virtually toward any specific cancer by phage display, the angiogenin-binding phages are thus universal "plug-and-play" tumor-homing cancer therapeutics.

Three decades of research on angiogenin: a review and perspective

As a member of the vertebrate-specific secreted ribonucleases, angiogenin (ANG) was first isolated and identified solely by its ability to induce new blood vessel formation, and now, it has been recognized to play important roles in various physiological and pathological processes through regulating cell proliferation, survival, migration, invasion, and/or differentiation. ANG exhibits very weak ribonucleolytic activity that is critical for its biological functions, and exerts its functions through activating different signaling transduction pathways in different target cells. A series of recent studies have indicated that ANG contributes to cellular nucleic acid metabolism. Here, we comprehensively review the results of studies regarding the structure, mechanism, and function of ANG over the past three decades. Moreover, current problems and future research directions of ANG are discussed. The understanding of the function and mechanism of ANG in a wide context will help to better delineate its roles in diseases, especially in cancer and neurodegenerative diseases.

FHL3 differentially regulates the expression of MyHC isoforms through interactions with MyoD and pCREB

In skeletal muscle, muscle fiber types are defined by four adult myosin heavy chain (MyHC) isoforms. Four and a half LIM domain protein 3 (FHL3) regulates myoblasts differentiation and gene expression by acting as a transcriptional co-activator or co-repressor. However, how FHL3 regulates MyHC expression is currently not clear. In this study, we found that FHL3 down-regulated the expression of MyHC 1/slow and up-regulated the expression of MyHC 2a and MyHC 2b, whereas no significant effect was found on MyHC 2x expression. MyoD and phosphorylated cAMP response element binding protein (pCREB) played important roles in the regulation of MyHC 1/slow and MyHC 2a expression by FHL3, respectively. FHL3 could interact with MyoD, CREB and pCREB in vivo. pCREB had stronger interaction with the cyclic AMP-responsive elements (CRE) of the MyHC 2a promoter compared with CREB, and FHL3 significantly affected the binding capacity of pCREB to CRE. We established a model in which FHL3 promotes the expression of MyHC 2a through CREB-mediated transcription and inhibits the expression of MyHC 1/slow by inhibiting MyoD transcription activity during myogenesis. Our data support the notion that FHL3 plays important roles in the regulation of muscle fiber type composition.

Angiogenin promotes U87MG cell proliferation by activating NF-κB signaling pathway and downregulating its binding partner FHL3

Angiogenin (Ang) is known to induce cell proliferation and inhibit apoptosis by cellular signaling pathways and its direct nuclear functions, but the mechanism of action for Ang in astrocytoma is not yet clear. Astrocytoma is the most frequent one among various neurogliomas, of which a subtype known as glioblastoma multiforme (GBM) is the most malignant brain glioma and seriously influences the life quality of the patients. The expression of Ang and Bcl-xL were detected in 28 cases of various grades of astrocytoma and 6 cases of normal human tissues by quantitative real-time PCR. The results showed that the expression of Ang and Bcl-xL positively correlated with the malignant grades. Cytological experiments indicated that Ang facilitated human glioblastoma U87MG cell proliferation and knock-down of endogenous Ang promoted cell apoptosis. Furthermore, Ang activated NF-κB pathway and entered the U87MG cell nuclei, and blocking NF-κB pathway or inhibiting Ang nuclear translocation partially suppressed Ang-induced cell proliferation. The results suggested that Ang participated in the regulation of evolution process of astrocytoma by interfering NF-κB pathway and its nucleus function. In addition, four and a half LIM domains 3 (FHL3), a novel Ang binding partner, was required for Ang-mediated HeLa cell proliferation in our previous study. We also found that knockdown of FHL3 enhanced IκBα phosphorylation and overexpression of Ang inhibited FHL3 expression in U87MG cells. Together our findings suggested that Ang could activate NF-κB pathway by regulating the expression of FHL3. In conclusion, the present study established a link between Ang and FHL3 proteins and identifies a new pathway for regulating astrocytoma progression.

Ribotrap analysis of proteins associated with FHL3 3'untranslated region in glioma cells

OBJECTIVE

To screen the proteins associated with four-and-a-half LIM domains 3 (FHL3) 3' untranslated region (3'UTR) in glioma cells.

METHODS

Western blot was adopted to detect the regulatory effect of poly(C)-binding protein 2 (PCBP2) on FHL3. Biotin pull-down and sliver staining were employed to screen and verify the candidate binding proteins of FHL3 3'UTR. Then liquid chromatography-tandem mass spectrometry (LC-MS/MS) and molecule annotation system were used to identify and analyze the candidate binding proteins. Immuno- precipitation was conducted to study the interaction between PCBP2 and polypyrimidine tract-binding protein 1 (PTBP1), a binding protein identified by LC-MS/MS.

RESULTS

PCBP2 could bind to FHL3 mRNA 3'UTR-A and inhibited the expression of FHL3 in T98G glioms cells. 22 candidate binding proteins were identified. Among them, there were 11 RNA binding proteins, including PCBP2. PTBP1 associated with FHL3 mRNA 3'UTR and interacted with PCBP2 protein.

CONCLUSIONS

PCBP2 and PTBP1 can both associate with FHL3 mRNA 3'UTR through forming a protein complex.

Identification and characterization of MT-1X as a novel FHL3-binding partner

Four and a half LIM domain protein 3 (FHL3) is a member of the FHL protein family that plays roles in the regulation of cell survival, cell adhesion and signal transduction. However, the mechanism of action for FHL3 is not yet clear. The aim of present study was to identify novel binding partner of FHL3 and to explore the underlying mechanism. With the use of yeast two-hybrid screening system, FHL3 was used as the bait to screen human fetal hepatic cDNA library for interacting proteins. Methionine-1X was identified as a novel FHL3 binding partner. The interaction between FHL3 and the full length MT-1X was further confirmed by yeast two-hybrid assay, co-immunoprecipitation and GST pull-down assays. Furthermore,the result demonstrated that MT-1X knockdown promoted the FHL3-induced inhibitory effect on HepG2 cells by regulating FHL3-mediated Smad signaling and involving in the modulation the expression of G2/M phase-related proteins through interaction with FHL3. These findings suggest that functional interactions between FHL3 and MT-1X may provide some clues to the mechanisms of FHL3-regulated cell proliferation.

RNA-binding protein PCBP2 modulates glioma growth by regulating FHL3

PCBP2 is a member of the poly(C)-binding protein (PCBP) family, which plays an important role in posttranscriptional and translational regulation by interacting with single-stranded poly(C) motifs in target mRNAs. Several PCBP family members have been reported to be involved in human malignancies. Here, we show that PCBP2 is upregulated in human glioma tissues and cell lines. Knockdown of PCBP2 inhibited glioma growth in vitro and in vivo through inhibition of cell-cycle progression and induction of caspase-3-mediated apoptosis. Thirty-five mRNAs were identified as putative PCBP2 targets/interactors using RIP-ChIP protein-RNA interaction arrays in a human glioma cell line, T98G. Four-and-a-half LIM domain 3 (FHL3) mRNA was downregulated in human gliomas and was identified as a PCBP2 target. Knockdown of PCBP2 enhanced the expression of FHL3 by stabilizing its mRNA. Overexpression of FHL3 attenuated cell growth and induced apoptosis. This study establishes a link between PCBP2 and FHL3 proteins and identifies a new pathway for regulating glioma progression.