Human endomucin is an endothelial marker

Therapeutic targeting of the tumor vasculature

A functional tumor vasculature is essential for tumor growth and metastasis and makes an attractive target for therapy. Both antiangiogenic and antivascular approaches are being developed for this purpose. In this article, the current antiangiogenic and antivascular approaches to cancer therapy, potential for their combination with radiotherapy, methods for identifying new targets on the tumor vasculature, and methods for evaluating new vascular-targeted strategies in in vivo model systems are reviewed.

Expression Pattern of the Novel Gene EG-1 in Cancer

PURPOSE

We recently discovered a novel gene responsive to tumor-conditioned media: endothelial-derived gene 1 (EG-1). Its transcript has been shown to be present in epithelial cells, as well as in endothelial cells. In this study, we examined the levels of EG-1 protein expression in breast, colon, prostate, and lung cancers, which constitute the four most common solid malignancies in the United States.

EXPERIMENTAL DESIGN

Polyclonal antibodies were generated that recognize the EG-1 peptide. These antibodies were used in immunoblot analysis, as well as immunohistochemistry of multiple human clinical specimens of cancer.

RESULTS

In immunoblots of whole cell lysates, EG-1 antibodies revealed the presence of a 22-kDa peptide. Immunohistochemistry of breast, colon, and prostate specimens showed higher levels of EG-1 peptides in cancer tissues, in comparison with their benign counterparts. However, EG-1 expression was minimal in both benign and malignant lung tissues.

CONCLUSIONS

Here, we demonstrated that the expression of EG-1 is elevated in cancerous in comparison to benign epithelial cells, as seen in immunohistochemistry of human pathological specimens. These observations collectively support the hypothesis that the novel gene EG-1 is associated with the malignant phenotype of the common epithelial-derived cancers of the breast, colon, and prostate.

Expression of endomucin, a novel endothelial sialomucin, in normal and diseased human skin

Endomucin is an endothelial sialomucin that was recently identified with the help of monoclonal antibodies raised against mouse endothelial cells. Cloning of human endomucin allowed us to generate monoclonal antibodies against soluble recombinant forms of human endomucin. In this study, we investigated the expression of this novel molecule in human skin under different conditions, using the monoclonal antibodies. In normal human skin, endomucin was detected for the monoclonal antibody L6H10 by immunoblotting, and immunohistologic analysis of wax-embedded sections revealed that this glycoprotein is expressed on capillaries, venules, and lymphatic vessels. Interestingly, staining of arterial endothelium was either weak or focal using the monoclonal antibodies against endomucin. In situ hybridization of normal human skin confirmed the expression pattern on the messenger RNA level obtained above. We further analyzed the expression of endomucin in skin biopsy specimens from patients with inflammatory skin diseases, such as atopic dermatitis, psoriasis, lichen planus, cutaneous lupus erythematosus, and T cell lymphoma as well as with vascular skin tumors, such as hemangioma, pyogenic granuloma, angiolipoma, Kaposi's sarcoma, and angiosarcoma. We found endomucin expressed on the endothelium of each tissue, concluding that this novel molecule is a new endothelial-specific marker in the study of normal and diseased human skin.

Chondromodulin I is dispensable during enchondral ossification and eye development

Chondromodulin I (chm-I), a type II transmembrane protein, is highly expressed in the avascular zones of cartilage but is downregulated in the hypertrophic region, which is invaded by blood vessels during enchondral ossification. In vitro and in vivo assays with the purified protein have shown chondrocyte-modulating and angiogenesis-inhibiting functions. To investigate chm-I function in vivo, we generated transgenic mice lacking chm-I mRNA and protein. Null mice are viable and fertile and show no morphological changes. No abnormalities in vascular invasion and cartilage development were detectable. No evidence was found for a compensating function of tendin, a recently published homologue highly expressed in tendons and also, at low levels, in cartilage. Furthermore, no differences in the expression of other angiogenic or antiangiogenic factors such as transforming growth factor beta1 (TGF-beta1), TGF-beta2, TGF-beta3, fibroblast growth factor 2, and vascular endothelial growth factor were found. The surprising lack of phenotype in the chm-I-deficient mice suggests either a different function for chm-I in vivo than has been proposed or compensatory changes in uninvestigated angiogenic or angiogenesis-inhibiting factors. Further analysis using double-knockout technology will be necessary to analyze the function of chm-I in the complex process of enchondral ossification.

Identification of a novel endothelial-derived gene EG-1

The identification of novel endothelial-derived genes is important in the study of angiogenesis, and may have potential uses in cancer diagnosis and treatment. We performed SSH (suppression subtractive hybridization) on control HUVECs (human umbilical vein endothelial cells) versus HUVECs exposed to tumor-conditioned media. We found that a novel cDNA (GenBank Accession No. AF358829) is differentially expressed in endothelial cells on Northern analysis, and named it endothelial-derived gene-1 (EG-1). This gene product is predicted to encode a 178-aa, 19.5-kDa protein, and is localized to chromosome 4. It has some homology to a mouse cDNA (94%) and a Drosophila cDNA (31%). On Northern analysis, endothelial cells express two EG-1 RNA species (1.2 and 2.4 kb). The expression of either transcripts is upregulated by endothelial cells when exposed to tumor conditioned media. This phenomenon is observed only under sparse conditions (50% confluency). Transcripts are present abundantly in highly vascular tissues such as placenta, testis, and liver. Interestingly, both Northern analysis and in situ hybridization studies show that this gene is expressed in other cell types as well, predominantly the epithelial type. Breast cancer, prostate cancer, and colon cancer cells show elevated expression of the higher 2.4-kb RNA form. Our data suggest that EG-1 is associated with a stimulated state in endothelial and epithelial cells, and may have a role in tumor angiogenesis.