Galectin-3 and L1 retrotransposons in human breast carcinomas

Selective elimination of long INterspersed element-1 expressing tumour cells by targeted expression of the HSV-TK suicide gene

In gene therapy, effective and selective suicide gene expression is crucial. We exploited the endogenous Long INterspersed Element-1 (L1) machinery often reactivated in human cancers to integrate the Herpes Simplex Virus Thymidine Kinase (HSV-TK) suicide gene selectively into the genome of cancer cells. We developed a plasmid-based system directing HSV-TK expression only when reverse transcribed and integrated in the host genome via the endogenous L1 ORF1/2 proteins and an Alu element. Delivery of these new constructs into cells followed by Ganciclovir (GCV) treatment selectively induced mortality of L1 ORF1/2 protein expressing cancer cells, but had no effect on primary cells that do not express L1 ORF1/2. This novel strategy for selective targeting of tumour cells provides high tolerability as the HSV-TK gene cannot be expressed without reverse transcription and integration, and high selectivity as these processes take place only in cancer cells expressing high levels of functional L1 ORF1/2.

Guardian of the Human Genome: Host Defense Mechanisms against LINE-1 Retrotransposition

Long interspersed element type 1 (LINE-1, L1) is a mobile genetic element comprising about 17% of the human genome, encoding a newly identified ORF0 with unknown function, ORF1p with RNA-binding activity and ORF2p with endonuclease and reverse transcriptase activities required for L1 retrotransposition. L1 utilizes an endonuclease (EN) to insert L1 cDNA into target DNA, which induces DNA double-strand breaks (DSBs). The ataxia-telangiectasia mutated (ATM) is activated by DSBs and subsequently the ATM-signaling pathway plays a role in regulating L1 retrotransposition. In addition, the host DNA repair machinery such as non-homologous end-joining (NHEJ) repair pathway is also involved in L1 retrotransposition. On the other hand, L1 is an insertional mutagenic agent, which contributes to genetic change, genomic instability, and tumorigenesis. Indeed, high-throughput sequencing-based approaches identified numerous tumor-specific somatic L1 insertions in variety of cancers, such as colon cancer, breast cancer, and hepatocellular carcinoma (HCC). In fact, L1 retrotransposition seems to be a potential factor to reduce the tumor suppressive property in HCC. Furthermore, recent study demonstrated that a specific viral-human chimeric transcript, HBx-L1, contributes to hepatitis B virus (HBV)-associated HCC. In contrast, host cells have evolved several defense mechanisms protecting cells against retrotransposition including epigenetic regulation through DNA methylation and host defense factors, such as APOBEC3, MOV10, and SAMHD1, which restrict L1 mobility as a guardian of the human genome. In this review, I focus on somatic L1 insertions into the human genome in cancers and host defense mechanisms against deleterious L1 insertions.

Association of new deletion/duplication region at chromosome 1p21 with intellectual disability, severe speech deficit and autism spectrum disorder-like behavior: an all-in approach to solving the DPYD enigma

We describe an as yet unreported neocentric small supernumerary marker chromosome (sSMC) derived from chromosome 1p21.3p21.2. It was present in 80% of the lymphocytes in a male patient with intellectual disability, severe speech deficit, mild dysmorphic features, and hyperactivity with elements of autism spectrum disorder (ASD).

Several important neurodevelopmental genes are affected by the 3.56 Mb copy number gain of 1p21.3p21.2, which may be considered reciprocal in gene content to the recently recognized 1p21.3 microdeletion syndrome. Both 1p21.3 deletions and the presented duplication display overlapping symptoms, fitting the same disorder category. Contribution of coding and non-coding genes to the phenotype is discussed in the light of cellular and intercellular homeostasis disequilibrium. In line with this the presented 1p21.3p21.2 copy number gain correlated to 1p21.3 microdeletion syndrome verifies the hypothesis of a cumulative effect of the number of deregulated genes - homeostasis disequilibrium leading to overlapping phenotypes between microdeletion and microduplication syndromes.

Although miR-137 appears to be the major player in the 1p21.3p21.2 region, deregulation of the DPYD (dihydropyrimidine dehydrogenase) gene may potentially affect neighboring genes underlying the overlapping symptoms present in both the copy number loss and copy number gain of 1p21. Namely, the all-in approach revealed that DPYD is a complex gene whose expression is epigenetically regulated by long non-coding RNAs (lncRNAs) within the locus. Furthermore, the long interspersed nuclear element-1 (LINE-1) L1MC1 transposon inserted in DPYD intronic transcript 1 (DPYD-IT1) lncRNA with its parasites, TcMAR-Tigger5b and pair of Alu repeats appears to be the “weakest link” within the DPYD gene liable to break. Identification of the precise mechanism through which DPYD is epigenetically regulated, and underlying reasons why exactly the break (FRA1E) happens, will consequently pave the way toward preventing severe toxicity to the antineoplastic drug 5-fluorouracil (5-FU) and development of the causative therapy for the dihydropyrimidine dehydrogenase deficiency.

Expression of galectin-3 correlates with apoptosis in pituitary adenoma cells

OBJECTIVE

To investigate the expressions of Galectin-3 (Gal-3), Bcl-2 and Bax in human pituitary adenomas, and to explore the interrelation among them.

METHODS

RT-PCR and immunohistochemistry were applied to detect the mRNA and protein expressions of Gal-3, Bcl-2 and Bax in surgically excised human pituitary adenoma tissues, including invasive and non-invasive pituitary adenomas, and the correlation analysis was performed.

RESULTS

The Gal-3 and Bcl-2 expressions in the invasive pituitary group were significantly higher than those in the non-invasive group, and the expression of Bax had no significant difference between the two groups. Pearsonos correlation analyses showed that the Gal-3 expression was positively correlated with Bcl-2, but was not correlated with Bax, which was inversely correlated with expression of Bcl-2.

CONCLUSION

Gal-3 may function through a cell death inhibition pathway involving Bcl-2 to enhance cell proliferation, which result in the invasive growth of pituitary adenoma. These results indicate that Gal-3 has an important role in pituitary tumor cell proliferation and may serves as a possible therapeutic target in treatment of pituitary tumors.

Potential for genomic instability associated with retrotranspositionally-incompetent L1 loci

Expression of the L1 retrotransposon can damage the genome through insertional mutagenesis and the generation of DNA double-strand breaks (DSBs). The majority of L1 loci in the human genome are 5'-truncated and therefore incapable of retrotransposition. While thousands of full-length L1 loci remain, most are retrotranspositionally-incompetent due to inactivating mutations. However, mutations leading to premature stop codons within the L1 ORF2 sequence may yield truncated proteins that retain a functional endonuclease domain. We demonstrate that some truncated ORF2 proteins cause varying levels of toxicity and DNA damage when chronically overexpressed in mammalian cells. Furthermore, transfection of some ORF2 constructs containing premature stop codons supported low levels of Alu retrotransposition, demonstrating the potential for select retrotranspositionally-incompetent L1 loci to generate genomic instability. This result suggests yet another plausible explanation for the relative success of Alu elements in populating the human genome. Our data suggest that a subset of retrotranspositionally-incompetent L1s, previously considered to be harmless to genomic integrity, may have the potential to cause chronic DNA damage by introducing DSBs and mobilizing Alu. These results imply that the number of known L1 loci in the human genome that potentially threaten its stability may not be limited to the retrotranspositionally active loci.

Galectin-3 in cancer

Galectin-3 (Gal-3) plays important roles in cell proliferation, adhesion, differentiation, angiogenesis and apoptosis in normal and pathologic tissues. Accumulated evidences indicate that Gal-3 is closely involved in tumor cell transformation, migration, invasion and metastasis. In this review, the associations of the expression and localization of Gal-3 as well as its potential action mechanism in tumorigenesis in a variety of cancers were summarized and concluded. Gal-3 is gaining its attraction as a potential new biomarker for the diagnosis, treatment and prognosis of certain tumors.

Galectin-3 regulates p21 stability in human prostate cancer cells

Galectin-3 (Gal-3) is a multifunctional protein involved in cancer through regulation of cell adhesion, cell growth, apoptosis and metastasis, while p21 (Cip1/WAF1) is a negative regulator of the cell cycle, involved in apoptosis, transcription, DNA repair and metastasis. The results presented here demonstrate for the first time that the level of Gal-3 protein is associated with the level of p21 protein expression in human prostate cancer cells and the effects of Gal-3 on cell growth and apoptosis were reversed by modulating p21 expression level. Furthermore, Gal-3 regulates p21 expression at the post-translational level by stabilizing p21 protein via the carbohydrate-recognition domain. This is the first report suggesting a molecular function not yet described for Gal-3 as the regulator of p21 protein stability. This study provides a unique insight into the relationship of these two molecules during prostate cancer progression, and may provide a novel therapeutic target.

L1 expression and regulation in humans and rodents

Long interspersed elements type 1 (LINE-1s, or L1s) have impacted mammalian genomes at multiple levels. L1 transcription is mainly controlled by its 5' untranslated region (5'UTR), which differs significantly among active human and rodent L1 families. In this review, L1 expression and its regulation are examined in the context of human and rodent development. First, endogenous L1 expression patterns in three different species-human, rat, and mouse-are compared and contrasted. A detailed account of relevant experimental evidence is presented according to the source material, such as cell lines, tumors, and normal somatic and germline tissues from different developmental stages. Second, factors involved in the regulation of L1 expression at both transcriptional and posttranscriptional levels are discussed. These include transcription factors, DNA methylation, PIWI-interacting RNAs (piRNAs), RNA interference (RNAi), and posttranscriptional host factors. Similarities and differences between human and rodent L1s are highlighted. Third, recent findings from transgenic mouse models of L1 are summarized and contrasted with those from endogenous L1 studies. Finally, the challenges and opportunities for L1 mouse models are discussed.

The reverse transcription inhibitor abacavir shows anticancer activity in prostate cancer cell lines

BACKGROUND

Transposable Elements (TEs) comprise nearly 45% of the entire genome and are part of sophisticated regulatory network systems that control developmental processes in normal and pathological conditions. The retroviral/retrotransposon gene machinery consists mainly of Long Interspersed Nuclear Elements (LINEs-1) and Human Endogenous Retroviruses (HERVs) that code for their own endogenous reverse transcriptase (RT). Interestingly, RT is typically expressed at high levels in cancer cells. Recent studies report that RT inhibition by non-nucleoside reverse transcriptase inhibitors (NNRTIs) induces growth arrest and cell differentiation in vitro and antagonizes growth of human tumors in animal model. In the present study we analyze the anticancer activity of Abacavir (ABC), a nucleoside reverse transcription inhibitor (NRTI), on PC3 and LNCaP prostate cancer cell lines.

PRINCIPAL FINDINGS

ABC significantly reduces cell growth, migration and invasion processes, considerably slows S phase progression, induces senescence and cell death in prostate cancer cells. Consistent with these observations, microarray analysis on PC3 cells shows that ABC induces specific and dose-dependent changes in gene expression, involving multiple cellular pathways. Notably, by quantitative Real-Time PCR we found that LINE-1 ORF1 and ORF2 mRNA levels were significantly up-regulated by ABC treatment.

CONCLUSIONS

Our results demonstrate the potential of ABC as anticancer agent able to induce antiproliferative activity and trigger senescence in prostate cancer cells. Noteworthy, we show that ABC elicits up-regulation of LINE-1 expression, suggesting the involvement of these elements in the observed cellular modifications.

Regulation of prostate cancer progression by galectin-3

Galectin-3, a beta-galactoside-binding protein, has been implicated in a variety of biological functions including cell proliferation, apoptosis, angiogenesis, tumor progression, and metastasis. The present study was undertaken to understand the role of galectin-3 in the progression of prostate cancer. Immunohistochemical analysis of galectin-3 expression revealed that galectin-3 was cleaved during the progression of prostate cancer. Galectin-3 knockdown by small interfering RNA (siRNA) was associated with reduced cell migration, invasion, cell proliferation, anchorage-independent colony formation, and tumor growth in the prostates of nude mice. Galectin-3 knockdown in human prostate cancer PC3 cells led to cell-cycle arrest at G(1) phase, up-regulation of nuclear p21, and hypophosphorylation of the retinoblastoma tumor suppressor protein (pRb), with no effect on cyclin D1, cyclin E, cyclin-dependent kinases (CDK2 and CDK4), and p27 protein expression levels. The data obtained here implicate galectin-3 in prostate cancer progression and suggest that galectin-3 may serve as both a diagnostic marker and therapeutic target for future disease treatments.

Immunohistochemical study of galectin-3 in mature and immature bull testis and epididymis

Galectin-3, a member of the β-galactoside-binding protein family, has been implicated in mammalian sperm maturation. We examined galectin-3 expression in the testis and epididymis of sexually mature and immature bulls. Western blot analysis showed varying levels of galectin-3 in the bull testis and epididymis, and galectin-3 immunoreactivity was higher in the mature testis and epididymis than in immature organs. Galectin-3 was primarily localized in interstitial cells of the immature bull testis and in the peritubular myoid and interstitial cells of the mature testis. In the immature epididymis head, galectin-3 was primarily in the principal and basal cells of the epithelium. In the mature epididymis head, moderate levels of galectin-3 were detected in the sperm, while low levels were found in the stereocilia, epithelium and connective tissue. In the immature epididymis body, moderate protein levels were detected in the principal cells, while lower levels were found in the basal cells. The mature epididymis body showed moderate levels of galectin-3 immunostaining in the stereocilia and epithelium, but low levels in the connective tissue. In the immature epididymis tail, only low levels of galectin-3 staining were found in the epithelium, whereas the mature epididymis tail showed high levels of galectin-3 in the principal cells, moderate levels in the basal cells and low levels in connective tissue. These findings suggest that galectin-3 expression plays a role in the maturation and activation of sperm in bulls.

Extravasation of leukocytes in comparison to tumor cells

The multi-step process of the emigration of cells from the blood stream through the vascular endothelium into the tissue has been termed extravasation. The extravasation of leukocytes is fairly well characterized down to the molecular level, and has been reviewed in several aspects. Comparatively little is known about the extravasation of tumor cells, which is part of the hematogenic metastasis formation. Although the steps of the process are basically the same in leukocytes and tumor cells, i.e. rolling, adhesion, transmigration (diapedesis), the molecules that are involved are different. A further important difference is that leukocyte interaction with the endothelium changes the endothelial integrity only temporarily, whereas tumor cell interaction leads to an irreversible damage of the endothelial architecture. Moreover, tumor cells utilize leukocytes for their extravasation as linkers to the endothelium. Thus, metastasis formation is indirectly susceptible to localization signals that are literally specific for the immune system. We herein compare the extravasation of leukocytes and tumor cells with regard to the involved receptors and the localization signals that direct the cells to certain organs and sites of the body.

Galectin-3 as a potential therapeutic target in tumors arising from malignant endothelia

Angiosarcoma (ASA) in humans and hemangiosarcoma (HSA) in dogs are deadly neoplastic diseases characterized by an aggressive growth of malignant cells with endothelial phenotype, widespread metastasis, and poor response to chemotherapy. Galectin-3 (Gal-3), a beta-galactoside-binding lectin implicated in tumor progression and metastasis, endothelial cell biology and angiogenesis, and regulation of apoptosis and neoplastic cell response to cytotoxic drugs, has not been studied before in tumors arising from malignant endothelia. Here, we tested the hypothesis that Gal-3 could be widely expressed in human ASA and canine HSA and could play an important role in malignant endothelial cell biology. Immunohistochemical analysis demonstrated that 100% of the human ASA (10 of 10) and canine HSA (17 of 17) samples analyzed expressed Gal-3. Two carbohydrate-based Gal-3 inhibitors, modified citrus pectin (MCP) and lactulosyl-l-leucine (LL), caused a dose-dependent reduction of SVR murine ASA cell clonogenic survival through the inhibition of Gal-3 antiapoptotic function. Furthermore, both MCP and LL sensitized SVR cells to the cytotoxic drug doxorubicin to a degree sufficient to reduce the in vitro IC(50) of doxorubicin by 10.7-fold and 3.6-fold, respectively. These results highlight the important role of Gal-3 in the biology of ASA and identify Gal-3 as a potential therapeutic target in tumors arising from malignant endothelial cells.

Computational and biological inference of gene regulatory networks of the LINE-1 retrotransposon

Computational approaches were used to define structural and functional determinants of a putative genetic regulatory network of murine LINE-1 (long interspersed nuclear element-1), an active mammalian retrotransposon that uses RNA intermediates to populate new sites throughout the genome. Polymerase (RNA) II polypeptide E AI845735 and mouse DNA homologous to Drosophila per fragment M12039 were identified as primary attractors. siRNA knockdown of the aryl hydrocarbon receptor NM_013464 modulated gene expression within the network, including LINE-1, Sgpl1, Sdcbp, and Mgst1. Genes within the network did not exhibit physical proximity and instead were dispersed throughout the genome. The potential impact of individual members of the network on the global dynamical behavior of LINE-1 was examined from a theoretical and empirical framework.

Intravascular cell-to-cell adhesive interactions and bone metastasis

Metastatic cancer spread to bones, causing intractable pain, pathological fractures, spinal cord compression, and ultimately death, represents massive clinical problem. Intravascular cell-to-cell heterotypic (between cancer and other types of cells) and homotypic (between cancer cells) adhesive interactions, leading to the establishment of metastatic deposits in bone marrow vasculature, represent important rate-limiting steps in bone metastasis. In this review, we discuss molecular and cellular mechanisms underpinning metastasis-associated intravascular cell-to-cell adhesive interactions, their role in a multi-step metastatic cascade, and a potential for therapeutic targeting of early metastasis-associated adhesive events.

Molecular and cellular basis of rheumatoid joint destruction

Rheumatoid arthritis (RA) is a chronic inflammatory disease associated with joint destruction. Synovial fibroblasts are key players in this pathological process. They favorise a pro-inflammatory environment in the synovial tissue, interact with the immune system and regulate the differentiation of monocytes into osteoclasts. Synovial hyperplasia is another characteristic of RA, reflecting not only an imbalance between proliferation and apoptosis, but also the migration of cells into the synovial tissue. Gene transfer experiments have been used as important tools for the understanding of molecular and cellular changes that characterize the activated RA synovial fibroblasts. Activated synovial fibroblasts can invade cartilage and bone. Synovial activation is driven by cytokines, such as TNFalpha and IL-1, as well as IL-15, 16, 17, 18, 22, 23, but also by cytokine-independent mechanisms that involve the innate immune system (i.e. TLRs), a unique communication network of microparticles and epigenetic changes (e.g. L1 retroelements).

The human LINE-1 retrotransposon creates DNA double-strand breaks

Long interspersed element-1 (L1) is an autonomous retroelement that is active in the human genome. The proposed mechanism of insertion for L1 suggests that cleavage of both strands of genomic DNA is required. We demonstrate that L1 expression leads to a high level of double-strand break (DSB) formation in DNA using immunolocalization of gamma-H2AX foci and the COMET assay. Similar to its role in mediating DSB repair in response to radiation, ATM is required for L1-induced gamma-H2AX foci and for L1 retrotransposition. This is the first characterization of a DNA repair response from expression of a non-long terminal repeat (non-LTR) retrotransposon in mammalian cells as well as the first demonstration that a host DNA repair gene is required for successful integration. Notably, the number of L1-induced DSBs is greater than the predicted numbers of successful insertions, suggesting a significant degree of inefficiency during the integration process. This result suggests that the endonuclease activity of endogenously expressed L1 elements could contribute to DSB formation in germ-line and somatic tissues.

Alterations in galectin-3 expression and distribution correlate with breast cancer progression: functional analysis of galectin-3 in breast epithelial-endothelial interactions

To define the role of galectin-3 in breast cancer progression, we have used a novel three-dimensional co-culture system that recapitulates in vivo reciprocal functional breast epithelial-endothelial cell-cell and cell-matrix interactions, and examined the expression of galectin-3 mRNA and protein in human breast tumors and xenografts. Galectin-3 is required for the stabilization of epithelial-endothelial interaction networks because immunoneutralization with galectin-3 antibodies abolishes the interactions in a dose-dependent manner. Co-culture of epithelial cells with endothelial cells results in increase in levels of secreted galectin-3 and presence of proteolytically processed form of galectin-3 in the conditioned media. In contrast, intracellular galectin-3 predominantly exists in the intact form. This difference in sensitivity to proteolytic processing of secreted versus intracellular galectin-3 probably arises from differences in accessibility of protease-sensitive sites, levels, and/or type of activated protease(s), and may be indicative of different functional roles for intact and processed galectin-3. To determine whether the proteolytically cleaved galectin-3 retains its ability to bind to endothelial cells, binding assays were performed with the full-length and matrix metallopeoteinase-2-cleaved recombinant galectin-3. Although a dose-dependent increase in binding to human umbilical vein endothelial cells was observed with both full-length and cleaved galectin-3, proteolytically cleaved galectin-3 displayed approximately 20-fold higher affinity for human umbilical vein endothelial cells as compared to the full-length protein. Examination of galectin-3 expression in breast tumors and xenografts revealed elevated levels of galectin-3 mRNA and protein in the luminal epithelial cells of normal and benign ducts, down-regulation in early grades of ductal carcinoma in situ (DCIS), and re-expression in peripheral tumor cells as DCIS lesions progressed to comedo-DCIS and invasive carcinomas. These data suggest that galectin-3 expression is associated with specific morphological precursor subtypes of breast cancer and undergoes a transitional shift in expression from luminal to peripheral cells as tumors progressed to comedo-DCIS or invasive carcinomas. Such a localized expression of galectin-3 in cancer cells proximal to the stroma could lead to increased invasive potential by inducing novel or better interactions with the stromal counterparts.

Galectin 3 and its binding protein in rheumatoid arthritis

OBJECTIVE

To characterize the expression pattern and role of galectin 3 and galectin 3 binding protein (G3BP) in rheumatoid arthritis (RA), in comparison with galectin 1, and to explore whether soluble galectin 3 and G3BP, investigated in serum, synovial fluid, or cell culture supernatant, are associated with disease.

METHODS

Synovial tissues from patients with RA or osteoarthritis (OA), as well as from healthy controls, were analyzed for galectins 1 and 3 and G3BP by in situ hybridization and immunohistochemistry. Levels of galectin 3 and G3BP in serum and synovial fluid from patients with RA and OA and controls, as well as in cell culture supernatants, were determined by enzyme-linked immunosorbent assay (ELISA). In vitro, the intracellular expression of galectin 3 in RA and OA synovial fibroblasts after modulation with tumor necrosis factor alpha (TNFalpha), interleukin-1beta (IL-1beta), and anti-CD40 monoclonal antibodies was measured by flow cytometry.

RESULTS

In RA, galectin 3 messenger RNA and protein stained throughout the synovial membrane, whereas G3BP was particularly expressed at sites of bone destruction. In contrast, the expression of galectin 1 was not uniform in different RA specimens, and was never found at sites of invasion. In OA and normal synovial tissues, only a small number of cells were positive for galectins and/or G3BP. Galectin 3 was elevated in RA sera and synovial fluids, whereas G3BP was increased in RA synovial fluids only. In RA, serum galectin 3 correlated with C-reactive protein levels, whereas G3BP was associated with joint destruction and/or synovial cell activation as measured by the levels of cartilage oligomeric matrix protein. In vitro, RA synovial fibroblasts showed an increased release of galectin 3 into culture medium, as measured by ELISA, but decreased secretion of G3BP. In RA synovial fibroblasts with low basal expression of galectin 3, TNFalpha increased its intracellular level in a dose-dependent manner. In contrast, IL-1beta or anti-CD40 monoclonal antibodies showed no effect.

CONCLUSION

Our data indicate that galectin 3 and G3BP are not only involved in inflammation, but also contribute to the activation of synovial fibroblasts. The intracellular accumulation of galectin 3 can be enhanced by TNFalpha. Thus, galectin 3 and G3BP represent novel markers of disease activity in RA.

Galectin-3 enhances cyclin D(1) promoter activity through SP1 and a cAMP-responsive element in human breast epithelial cells

Galectin-3 is a multifunctional carbohydrate-binding protein found in the nucleus, cytoplasm and the extracellular milieu. Nuclear galectin-3 expression is associated with cell proliferation, and its role in pre-mRNA splicing has been suggested. In this report, we investigated the role of galectin-3 on cyclin D(1) gene expression, a critical inducer of the cell cycle and a potential oncogene in human cancer. We found that galectin-3 induces cyclin D(1) promoter activity in human breast epithelial cells independent of cell adhesion through multiple cis-elements, including the SP1 and CRE sites. We present evidence that galectin-3 induction of the cyclin D(1) promoter may result from enhancement/stabilization of nuclear protein-DNA complex formation at the CRE site of the cyclin D(1) promoter. We also show that galectin-3 co-operates with, but does not depend on, pRb for cyclin D(1) promoter activation. The present study reveals a growth promoting activity of galectin-3 through cyclin D(1) induction, and suggests a novel function of nuclear galectin-3 in the regulation of gene transcription.

Galectin-3 translocates to the perinuclear membranes and inhibits cytochrome c release from the mitochondria. A role for synexin in galectin-3 translocation

Galectin-3 is a multifunctional oncogenic protein found in the nucleus and cytoplasm and also the extracellular milieu. Although recent studies demonstrated an anti-apoptotic activity of galectin-3, neither the functional site nor the mechanism of how galectin-3 regulates apoptosis is known. In this study, we examined the subcellular localization of galectin-3 during apoptosis and investigated its anti-apoptotic actions. We report that galectin-3 translocates to the perinuclear membrane following a variety of apoptotic stimuli. Confocal microscopy and biochemical analysis revealed that galectin-3 is enriched in the mitochondria and prevents mitochondrial damage and cytochrome c release. Using a yeast two-hybrid system, we screened for galectin-3-interacting proteins that regulate galectin-3 localization and anti-apoptotic activity. Synexin, a Ca(2+)- and phospholipid-binding protein, was one of the proteins identified. We confirmed direct interaction between galectin-3 and synexin by glutathione S-transferase pull-down assay in vitro. We showed that galectin-3 failed to translocate to the perinuclear membranes when expression of synexin was down-regulated using an oligodeoxyribonucleotide complementary to the synexin mRNA, suggesting a role for synexin in galectin-3 trafficking. Furthermore, synexin down-regulation abolished anti-apoptotic activity of galectin-3. Taken together, these results suggest that synexin mediates galectin-3 translocation to the perinuclear mitochondrial membranes, where it regulates mitochondrial integrity critical for apoptosis regulation.

Galectin-3 protects human breast carcinoma cells against nitric oxide-induced apoptosis: implication of galectin-3 function during metastasis

Galectin-3 is a beta-galactoside-binding protein which regulates many biological processes including cell adhesion, migration, cell growth, tumor progression, metastasis, and apoptosis. Although the exact function of galectin-3 in cancer development is unclear, galectin-3 expression is associated with neoplastic progression and metastatic potential. Since studies have suggested that tumor cell survival in microcirculation determines the metastatic outcome, we examined the effect of galectin-3 overexpression in human breast carcinoma cell survival using the liver ischemia/reperfusion metastasis model. While the majority of control cells died by hepatic ischemia/reoxygenation, nearly all of galectin-3 overexpressing cells survived. We showed that galectin-3 inhibits nitrogen free radical-mediated apoptosis, one of the major death pathways induced during hepatic ischemia/reperfusion. Galectin-3 inhibition of apoptosis involved protection of mitochondrial integrity, inhibition of cytochrome c release and caspase activation. Taking these results together with the previous observation that galectin-3 inhibits apoptosis induced by loss of cell adhesion, we propose that galectin-3 is a critical determinant for anchorage-independent and free radical-resistant cell survival during metastasis.

Retrotransposable L1 elements expressed in rheumatoid arthritis synovial tissue: association with genomic DNA hypomethylation and influence on gene expression

OBJECTIVE

Rheumatoid arthritis (RA) is characterized by a progressive destruction of joints by invasive synovial fibroblasts (SF). We searched for retroviral sequences in RA synovial fluid pellets, identified a sequence similar to that of open reading frame 2 (ORF2)/L1 retrotransposable elements, explored the expression of L1 in RA synovial tissues and cultured RA SF, and investigated the link to genomic DNA hypomethylation and the influence of functional L1 on gene expression.

METHODS

RA synovial fluid pellets were screened by reverse transcriptase-polymerase chain reaction (RT-PCR) using degenerated pol primers. The sequences were identified by GenBank search. Riboprobes to ORF2/L1 and galectin-3 and antibodies to the ORF1/L1-related p40 protein were used for in situ hybridization and immunohistochemistry of synovial tissues and cultured RA SF. Real-time quantitative RT-PCR was used for detecting ORF1 messenger RNA (mRNA). Since DNA hypomethylation occurs in inflammatory diseases, we incubated cells with the methylation inhibitor 5-aza-2'-deoxycytidine (5-azaC) and compared RA SF and osteoarthritis (OA) SF. L1-negative RA SF were transfected with the functional L1.2 construct, and differential gene expression was analyzed by subtractive hybridization combined with nested PCR.

RESULTS

RNA sequences similar to those of ORF2/L1 retrotransposable elements, THE1 transposon, human endogenous retrovirus (ERV)-E, human ERV-HC2, and gibbon ape leukemia virus pol genes were isolated from different RA synovial fluid pellets. In RA synovial tissues, ORF2/L1 transcripts were detected in the sublining layer and at sites of cartilage and bone destruction. Galectin-3 mRNA and L1-related ORF1/ p40 protein showed similar expression patterns. In contrast, OA synovial tissues in situ and cultures in vitro were negative. Real-time quantitative RT-PCR confirmed the presence of ORF1 mRNA in cultured RA SF (30-300-fold the amount in normal SF), demonstrating the existence of a nondegenerated and functional L1 element. In vitro, the majority of RA SF expressed ORF2/L1 mRNA. After incubation of SF with 5-azaC, L1 mRNA appeared in a time- and dose-dependent manner. Compared with OA SF, RA SF were more sensitive to 5-azaC. After transfection of RA SF with a functional L1.2 element, human stress-activated protein kinase 2 delta (SAPK2delta [or SAPK4]), met protooncogene, and galectin-3 binding protein genes were differentially expressed. The transcription of the SAPK2delta gene, favored also by DNA hypomethylation in vitro, was confirmed in RA synovial tissues.

CONCLUSION

Taken together, these data suggest that L1 elements and SAPK2delta pathways play a role in the activation of RA SF.

Galectin-3 expression in various thyroid neoplasms and its possible role in metastasis formation

Galectin-3 is a member of the beta-galactoside-binding protein family that plays an important role in cell-cell adhesion and in cell-matrix interaction. We have examined the expression of galectin-3 in normal, adenomatous, and malignant thyroid tissues and also in metastatic lesions. Galectin-3 was rarely expressed in normal thyroid tissue but was abundant in the cytoplasm of the neoplastic lesions. Among neoplastic lesions, galectin-3 was expressed to a greater extent in follicular carcinomas than in follicular adenomas and was present in greater amounts in papillary carcinomas than in follicular adenomas or carcinomas. Primary lesions of papillary carcinoma with metastasis contained significantly higher concentrations of galectin-3 than tumors of this type without metastases. However, the expression of galectin-3 was significantly decreased in metastatic lesions in the lymph nodes compared with their primary lesions. From these results, we assumed that galectin-3 works in different ways at different stages of thyroid neoplasm proliferation. Among primary tumors, galectin-3 expression is significantly different in 3 histological types. However, the continuity of progression among these tumors is not yet proven. In later stages, decreased expression of galectin-3 may aid the release of cancer cells from the primary lesions for invasion and metastasis.

Galectin-3 induces endothelial cell morphogenesis and angiogenesis

Increasing evidence suggests that carbohydrate-binding proteins play an essential role in tumor growth and metastasis. However, conflicting results on their function in the regulation of cell proliferation and differentiation during angiogenesis have been reported. We have examined the role of galectin-3 in the regulation of human umbilical vein endothelial cell proliferation, differentiation, migration, and neovascularization. Galectin-3, a carbohydrate-binding protein, with specificity for type 1 and 11 ABH blood group epitopes and polylactosamine glycan containing cell surface glycoproteins, is the major nonintegrin cellular laminin-binding protein. Because galectin-3 expression was shown to be associated in some tumor systems with metastasis, we questioned whether it induces endothelial cell morphogenesis. Here we show that galectin-3 affects chemotaxis and morphology and stimulates capillary tube formation of HUV-EC-C in vitro and angiogenesis in vivo. Endothelial cell morphogenesis is a carbohydrate-dependent process, as it is neutralized by specific sugars and antibodies. These findings demonstrate that endothelial cell surface carbohydrate recognition event(s) can induce a signaling cascade leading to the differentiation and angiogenesis of endothelial cells.