Enhanced Expression of the Tie Receptor Tyrosine Kinase Messenger RNA in the Vascular Endothelium of Metastatic Melanomas

Abstract

Angiogenesis of human melanomas has been the focus of intense interest since it was shown that the spread and prognosis of primary tumors is correlated with their vascularization (N. Weidner, J. P. Semple, W. R. Welch, and J. Folkman, N. Engl. J. Med., 324: 1–8, 1991). Basic fibroblast growth factor (bFGF) and its high-affinity receptor FGFR-1 have been implicated in melanoma growth and angiogenesis (R. Halaban, Y. Funasaka, J. Lee, J. Rubin, D. Ron, and D. Birnbaum, Fibroblast Growth Factors in Normal and Malignant Melanocytes, pp. 232–243. New York: The New York Academy of Sciences, 1991). We have studied the expression of the Tie endothelial cell receptor tyrosine kinase mRNA in skin and primary cutaneous melanomas as well as in their skin and brain metastases by in situ hybridization. The Tie probe hybridized very weakly with the vascular endothelium of capillaries of normal skin, while it was detected in larger arteries and veins as well as in capillaries around sweat glands. However, capillaries and medium-sized vessels within cutaneous and brain metastases of melanoma were strongly positive for Tie mRNA. In contrast, endothelial cells contained very little or no FGFR-1 transcripts, whereas abundant FGFR-1 mRNA was present in melanoma tumor cells and in fibrovascular stroma. In agreement with these findings, a Tie-specific amplified cDNA band was obtained by reverse transcription-polymerase chain reaction from melanoma metastases but not from normal skin. These results suggest a role for the Tie receptor in the angiogenesis associated with melanoma metastases.