Mutant p53 Correlates with Reduced Expression of Thrombospondin-1, Increased Angiogenesis, and Metastatic Progression in Melanoma

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Abstract
On the basis of reports linking mutant p53 (mp53) to decreased expression of the angiogenesis inhibitor thrombospondin-1 (TSP-1) and increased angiogenesis, we compared primary and metastatic melanoma tumor specimens to determine if these factors were associated with metastatic progression. Western blotting, immunohistochemistry (IHC), and image analysis (IA) techniques were employed to evaluate the relationship between p53 status and TSP-1 expression in Zaz and M14 melanoma cell lines, and among p53, TSP-1, and angiogenesis in primary and metastatic melanomas. Zaz cells expressed wild-type p53 (WT p53) and high levels of TSP-1, while the M14 cells expressed mp53 and low TSP-1 levels. Examination of clinical melanoma specimens (N = 99) revealed an incidence of mp53 of 48%. Specimens with WT p53 (N = 46) expressed significantly higher mean levels of TSP-1 (41 +/- 27 vs. 21 +/- 24; p = 0.0004), and lower microvessel counts per 200x field (25 +/- 17 vs. 40 +/- 20; p = 0.0001) than tumors expressing mp53 (N = 42). A significantly higher incidence of mp53 expression was seen in metastatic tumors (64%, 37/58) than in primary tumors (27%, 11/41)(p < 0.0005). Primary tumors specimens had higher levels of TSP-1 (40 +/- 27 vs. 25 +/- 25; p = 0.0054) and lower microvessel counts (26 +/- 18 vs. 39 +/- 20, p = 0.0013) than metastatic tumors. These data suggest that acquisition of mp53, decreased TSP-1, and increased microvessel infiltration may be interrelated and associated with the metastatic phenotype in malignant melanoma.