TMEFF2 is an androgen-regulated gene exhibiting antiproliferative effects in prostate cancer cells

A truncated isoform of TMEFF2 encodes a secreted protein in prostate cancer cells

The transmembrane protein TMEFF2, also known as tomoregulin or TENB2, has been proposed as a potential immunotherapeutic target for the treatment of prostate cancer. Much attention has focused on its limited tissue distribution, with strong expression seen only in the brain and the prostate. Here we describe the identification of a novel splice variant of TMEFF2 expressed both in the normal prostate and in prostate cancer. This variant encodes an isoform of TMEFF2 that is truncated after the first four coding exons, eliminating both the EGF-like and the transmembrane domains. Fusion of GFP to this isoform demonstrated that this variant transcript produces a truncated TMEFF2 protein (TMEFF2-S). In contrast to full-length TMEFF2-GFP, the truncated TMEFF2-S-GFP fusion protein was enriched in cytosolic granules, showed no staining at the plasma membrane, and was secreted into the medium of transfected cells grown in tissue culture. These results indicate that a truncated isoform of TMEFF2 is expressed from this locus. This secreted form of TMEFF2 may functionally interact with full-length TMEFF2, or its binding partners, and may also influence current immune-based treatment strategies.

CpG island hypermethylation in progression of esophageal and gastric cancer

The upper gastrointestinal (GI) cancers have various carcinogenic pathways and precursor lesions, such as dysplasia for esophageal squamous cell carcinoma, Barrett esophagus for esophageal adenocarcinoma, and intestinal metaplasia for the intestinal-type of gastric cancer. Recently, many epigenetic events in carcinogenic pathways have been revealed, along with genomic and genetic alterations. This information has provided deeper insight into an understanding of the mechanisms of upper GI carcinogenesis. Moreover, detection methods of aberrant methylation have been applied to clinical fields to stratify high-risk groups, detect early cancer, and to predict clinical outcomes. In this review, a variety of information is summarized regarding gene hypermethylation in esophageal and gastric cancer.

Gene expression in the LNCaP human prostate cancer progression model: progression associated expression in vitro corresponds to expression changes associated with prostate cancer progression in vivo

Identification of the genes involved in prostate cancer (PCa) progression to a virulent and androgen-independent (AI) form is a major focus in the field. cDNA microarray was used to compare the gene expression profile of the indolent, androgen sensitive (AS) LNCaP PCa cell line to the aggressively metastatic, AI C4-2. Thirty-eight unique sequences from a 6388 cDNA array were found differentially expressed (> or =2-fold, 95% CI). The expression of 14 genes was lower in C4-2 than in LNCaP cells, while the reverse was true for 24 genes. Twelve genes were validated using Q-PCR, Western blotting and immunohistochemistry (IHC) of LNCaP and C4-2 xenograft. Q-PCR showed that 10 of 12 (83.3%) genes had similar patterns of expression to the array (LNCaP>C4-2: TMEFF2, ATP1B1, IL-8, BTG1, BChE, NKX3.1; LNCaP<C4-2: BNIP3, TM4SF1, AMACR, UCH-L1). By Western blot, 4/5 genes examined: TMEFF2, NKX3.1, AMACR, and UCH-L1, not IL-8, were consistent with RNA profiling. Protein expression levels were confirmed in human tumor xenografts using IHC. A large proportion of the markers found in this expression profile is consistent with those recently identified in human PCa tissues along with several novel genes that remain to be examined. These data further demonstrate the utility of the LNCaP human PCa progression model as a tool to investigate the phenotypic changes required for the progression to AI and metastasis.

DNA methylation-associated inactivation of TGFbeta-related genes DRM/Gremlin, RUNX3, and HPP1 in human cancers

The transforming growth factor β (TGFβ)-signalling pathway is deregulated in many cancers. We examined the role of gene silencing via aberrant methylation of DRM/Gremlin and HPP1, which inhibit TGFβ signalling, and RUNX3, which facilitates TGFβ-signalling, of all genes that are thought to be tumour suppressors, are aberrantly expressed, and are thus thought to have important role in human cancers. We examined DRM/Gremlin mRNA expression in 44 cell lines and the promoter methylation status of DRM/Gremlin, HPP1, and RUNX3 in 44 cell lines and 511 primary tumours. The loss of DRM/Gremlin mRNA expression in human cancer cell lines is associated with DNA methylation, and treatment with the methylation inhibitor-reactivated mRNA expression (n=13). Methylation percentages of the three genes ranged from 0–83% in adult tumours and 0–50% in paediatric tumours. Methylation of DRM/Gremlin was more frequent in lung tumours in smokers, and methylation of all three genes was inversely correlated with prognosis in patients with bladder or prostate cancer. Our results provide strong evidence that these TGFβ-related genes are frequently deregulated through aberrant methylation in many human malignancies.

Targeting Tomoregulin for Radioimmunotherapy of Prostate Cancer

Radiotherapy is an effective approach for the treatment of local prostate cancer. However, once prostate cancer metastasizes, radiotherapy cannot be used due to the distribution of multiple metastases to lymph nodes and bones. In contrast, radioimmunotherapy should still be efficacious in metastatic prostate cancer as radioisotopes are brought to tumor cells by targeting antibodies. Here we identify and validate a prostate-expressed molecule, tomoregulin, as a target for radioimmunotherapy of prostate cancer. Tomoregulin is a transmembrane protein selectively expressed in the brain, prostate, and prostate cancer, but not expressed in other normal tissues. Immunohistochemical studies of tomoregulin protein in clinical samples show its location in the luminal epithelium of normal prostate, benign prostatic hyperplasia, and prostatic intraepithelial neoplasia. More importantly, the tomoregulin protein is expressed in primary prostate tumors and in their lymph node and bone metastases. The nature of tomoregulin as a transmembrane protein and its tissue-specific expression make tomoregulin an attractive target for radioimmunotherapy, in which tomoregulin-specific antibodies will deliver a radioisotope to prostate tumor cells and metastases. Indeed, biodistribution studies using a prostate tumor xenograft model showed that the (111)In-labeled anti-tomoregulin antibody 2H8 specifically recognizes tomoregulin protein in vivo, leading to a strong tumor-specific accumulation of the antibody. In efficacy studies, a single i.p. dose of 150 microCi (163 microg) (90)Y-labeled 2H8 substantially inhibits the growth rate of established LNCaP human prostate tumor xenograft in nude mice but produces no overt toxicity despite cross-reactivity of 2H8 with mouse tomoregulin. Our data clearly validate tomoregulin as a target for radioimmunotherapy of prostate cancer.

Preclinical validation of anti-TMEFF2-auristatin E–conjugated antibodies in the treatment of prostate cancer

Current treatments for advanced stage, hormone-resistant prostate cancer are largely ineffective, leading to high patient mortality and morbidity. To fulfill this unmet medical need, we used global gene expression profiling to identify new potential antibody-drug conjugate (ADC) targets that showed maximal prostate cancer-specific expression. TMEFF2, a gene encoding a plasma membrane protein with two follistatin-like domains and one epidermal growth factor–like domain, had limited normal tissue distribution and was highly overexpressed in prostate cancer. Immunohistochemistry analysis using a specific monoclonal antibody (mAb) to human TMEFF2 showed significant protein expression in 74% of primary prostate cancers and 42% of metastatic lesions from lymph nodes and bone that represented both hormone-naïve and hormone-resistant disease. To evaluate anti-TMEFF2 mAbs as potential ADCs, one mAb was conjugated to the cytotoxic agent auristatin E via a cathepsin B–sensitive valine-citrulline linker. This ADC, Pr1-vcMMAE, was used to treat male severe combined immunodeficient mice bearing xenografted LNCaP and CWR22 prostate cancers expressing TMEFF2. Doses of 3 to 10 mg/kg of this specific ADC resulted in significant and sustained tumor growth inhibition, whereas an isotype control ADC had no significant effect. Similar efficacy and specificity was shown with huPr1-vcMMAE, a humanized anti-TMEFF2 ADC. No overt in vivo toxicity was observed with either murine or human ADC, despite significant cross-reactivity of anti-TMEFF2 mAb with the murine TMEFF2 protein, implying minimal toxicity to other body tissues. These data support the further evaluation and clinical testing of huPr1-vcMMAE as a novel therapeutic for the treatment of metastatic and hormone-resistant prostate cancer.

Tomoregulin-1 (TMEFF1) inhibits nodal signaling through direct binding to the nodal coreceptor Cripto

Transforming growth factor beta (TGF-beta) signals regulate multiple processes during development and in adult. We recently showed that tomoregulin-1 (TMEFF1), a transmembrane protein, selectively inhibits nodal but not activin in early Xenopus embryos. Here we report that TMEFF1 binds to the nodal coreceptor Cripto, but does not associate with either nodal or the type I ALK (activin receptor-like kinase) 4 receptor in coimmunoprecipitation assays. The inhibition of the nodal signaling by TMEFF1 in Xenopus ectodermal explants is rescued with wild-type but not mutant forms of Cripto. Furthermore, we show that the Cripto-FRL1-Cryptic (CFC) domain in Cripto, which is essential for its binding to ALK4, is also important for its interaction with TMEFF1. Our results demonstrate for the first time that nodal signaling can be regulated by a novel mechanism of blocking the Cripto coreceptor.

Repression of the TMEFF2 promoter by c-Myc

TMEFF2 is a novel transmembrane protein, containing two follistatin domains and an epidermal growth factor-like motif that is mainly expressed in the prostate and brain. Recently, we showed that expression of TMEFF2 could inhibit prostate cancer cell growth. In addition, the TMEFF2 gene is frequently hypermethylated in human tumor cells, suggesting that it might be a tumor suppressor gene. We cloned the 5'-flanking region of the human TMEFF2 gene and using a luciferase reporter assay showed that it contains a functional promoter. The 0.7 kb region upstream to the TMEFF2 transcription start site encompasses the minimal promoter required for TMEFF2 expression. Sequence analysis of the TMEFF2 promoter revealed potential binding sites for several transcription factors including Sp1 and an E-box that could be recognized by c-Myc. An inverse correlation between TMEFF2 and c-Myc expression was found in CWR22 prostate xenografts. Reporter gene and mobility shift assays demonstrated that c-Myc could repress TMEFF2 gene expression through its cognate site. In light of the probable role of TMEFF2 in inhibiting cell growth, its suppression may contribute to the oncogenic properties of c-Myc.

TMEFF1 and brain tumors

TMEFF1 is a novel transmembrane protein, containing two follisatin domains and an epidermal growth factor-like region. These structural domains suggest a role for TMEFF1 in growth factor signaling. TMEFF1 fused to enhanced green fluorescent protein revealed that TMEFF1 is expressed on the cell membrane. Northern analysis of normal human tissue showed that TMEFF1 is predominantly expressed in the brain. Study of cancer cell lines from different tissues including the brain, demonstrated moderate to low levels of TMEFF1 in most of these transformed cell lines. Furthermore, quantitative real-time RT-PCR analysis of 54 brain tumors showed that most of these tumors (96%) had lower levels of TMEFF1 expression than normal brain tissue. Interestingly, ectopic expression of TMEFF1 in brain cancer cells resulted in their growth inhibition. These data suggest that TMEFF1 may behave as a tumor suppressor gene in brain cancers.