Tumorigenicity of the mixed spindle-epithelioid SP6.5 and epithelioid TP17uveal melanoma cell lines is differentially related to alpha 5 beta 1 integrin expression

Purpose. It has been suggested that the epithelioid morphology and high agg ressiveness that is typical of the uveal melanoma cell line TP17 is depende nt on the loss of alpha5 beta1 integrin expression at the cell surface. The purpose of the current study was to test this hypothesis in the TP17 cell line and investigate the role this integrin may play in the tumorigenicity of the SP6.5 cells, a mixed spindle-epithelioid culture-type human uveal me lanoma that shows tumorigenic properties clearly distinct from that of TP17 cells. Methods. Expression of the alpha5 integrin subunit was restored in the alph a5-TP17 cell line by stably transfecting the cells with a recombinant plasm id encoding the integrin subunit. Flow cytometry and adhesion assays on fib ronectin (FN)-coated culture plates were used to monitor alpha5 expression in the cells. The effect of alpha5 expression on both tumorigenicity and ce ll proliferation was evaluated in vivo in nude mice. In vitro growth proper ties of the alpha5(+) TP17 cells was evaluated by cell counting and compare d with that of the alpha5 parental TP17 cell line. The influence exerted by the alpha5 integrin subunit on the tumorigenic and proliferative propertie s of the SP6.5 cells was evaluated in vivo in nude mice by exposing the cel ls to increasing doses of a blocking antibody directed against the alpha5-s ubunit before subcutaneous injection, and compared with the results obtaine d with untreated SP6.5 cells. Results. Expression of the alpha5 integrin subunit in the alpha5-TP17 cells was successfully achieved, as evidenced by both flow cytometry and adhesio n assays on FN-coated culture plates. Restoring expression of alpha5 in TP1 7 cells enhanced epithelioid cell morphology and increased the growth prope rties of this cell line in vivo. The ability of the SP6.5 cells to yield su bcutaneous tumors was found to be concentration dependent and was reduced i n a dose-dependent manner when the cells were exposed to the anti-alpha5 bl ocking antibody. Conclusions. Restoring expression of alpha5 in the alpha5-negative TP17 uve al melanoma cell line influenced the proliferative properties of these cell s but did not alter its tumorigenic potential. In contrast. the ability of the SP6.5 cells to yield tumors in vivo in nude mice appeared to be related to expression of this integrin.