Vascular endothelial growth factors VEGF-B and VEGF-C are expressed in human tumors

Abstract

The growth of solid tumors is dependent on angiogenesis, the formation of new blood vessels. Vascular endothelial growth factor (VEGF) is a secreted endothelial-cell-specific mitogen. We have recently characterized two novel endothelial growth factors with structural homology to VEGF and named them VEGF-B and VEGF-C. To further define the roles of VEGF-B and VEGF-C, we have studied their expression in a variety of human tumors, both malignant and benign. VEGF-B mRNA was detected in most of the tumor samples studied, and the mRNA and the protein product were localized to tumor cells. Endothelial cells of tumor vessels were also immunoreactive for VEGF-B, probably representing the binding sites of the VEGF-B polypeptide secreted by adjacent tumor cells. VEGF-C mRNA was detected in approximately one-half of the cancers analyzed. Via in situ hybridization, VEGF-C mRNA was also localized to tumor cells. All lymphomas studied contained low levels of VEGF-C mRNA, possibly reflecting the cell-specific pattern of expression of the VEGF-C gene in the corresponding normal cells. The expression of VEGF-C is associated with the development of lymphatic vessels, and VEGF-C could be an important factor regulating the mutual paracrine relationships between tumor cells and lymphatic endothelial cells. Furthermore, VEGF-C and VEGF-B can, similarly to VEGF, be involved in tumor angiogenesis.

Figure 1.

Northern blot analysis of the expression of VEFG-B (1.4 kb), VEGF-C (2.4 kb), and VEGF (4.5 and 3.7 kb) mRNAs in human cancers. Hybridization was carried out with a pool of radiolabeled inserts for the three cDNAs, and the migration of the gene-specific mRNA bands are indicated. The criteria used for the semiquantitative evaluation of the mRNA expression levels are also shown. Lane 1, positive control PC-3 mRNA; lane 2, primary cutaneous melanoma; lane 3, melanoma metastasis; lane 4, ductal breast carcinoma; lane 5, ductal breast carcinoma; lane 6, squamous cell head and neck carcinoma, primary; lane 7, squamous cell head and neck carcinoma, metastasis; lane 8, sarcoma; lane 9, sarcoma. Note the differential regulation of the mRNAs, for example, the lack of VEGF mRNA in lanes 3 and 6.

Figure 2.

In situ hybridization analysis of VEGF-B and VEGF-C mRNAs in a head and neck carcinoma. Dark-field (A, C, and E) and light-field (B, D, and F) exposures are shown. Magnification, ×110. Insets: Higher magnification (×800). Note that the signals originate from the squamous cell carcinoma cells.

Figure 3.

Immunohistochemical analysis of VEGF-B protein. Immunohistochemical staining of ductal breast carcinoma (A and B), malignant melanoma (E and F), and fibrosarcoma (G and H). VEGF-B protein is observed in the carcinoma cells (arrowheads) and in the endothelial cells of tumor microvessels (arrows). Negative controls include staining of the ductal breast carcinoma with preimmune serum (C) as well as with VEGF-B polypeptide-blocked antiserum (D). Magnification, ×110 (A, C, D, E, and G) and ×250 (B, F, and H).