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M. Lessard, S. Landreville, S. Leclerc, C. Salesse, S. Guérin; Expression of the Gene Encoding the 4 Integrin Subunit Is Abnormally Regulated in Metastatic Uveal Melanoma. Invest. Ophthalmol. Vis. Sci. 2007;48(13):4757.
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© ARVO (1962-2015); The Authors (2016-present)
Uveal melanoma is the most frequent primary intraocular tumor in the adult population. The metastatic ability of uveal melanoma is particularly elevated as over 50% of the patients with this type of cancer will also develop metastases to the liver. The exact molecular events involved in the metastatic progression of uveal melanoma still remain unclear. Integrins, a family of receptors composed of noncovalently associated α and ß subunits, contribute to cancer invasion and metastasis mostly by their ability to interact with the extracellular matrix. In a survey of integrins expression that we recently conducted in an array of uveal melanoma cell lines, expression of the α4 integrin subunit was found to be abnormally elevated in a liver-derived metastatic cell line (H79) but not in poorly invasive primary uveal melanoma cells lines that have no metastatic properties (SP6.5, SP8.0 and TP31). The aim of this study was to investigate whether PAX-6, a transcription factor that we recently reported to be required for proper expression of the α4 gene expression, may contribute to the differential expression of the α4 integrin subunit gene in uveal melanoma.
Cell-surface expression of α4 was monitored in all uveal melanoma cell lines by FACS analyses. Western blot analyses were conducted to follow the expression of PAX-6 in both poorly (SP6,5, SP8.0, TP31) and highly invasive (H79) cell lines. Electrophoretic mobility shift assays (EMSAs) were conducted to monitor DNA binding of PAX-6. The regulatory influence of PAX-6 was examined either by cotransfection of α4-CAT recombinant constructs together with a PAX-6 expression plasmid, or by inhibition of PAX-6 expression through RNAi.
The α4 promoter directed high level of CAT expression only in the H79 metastatic cell line. PAX-6 was found to be expressed by both poorly and highly invasive uveal melanoma cell lines. On the other hand, cell surface expression of α4 integrin subunit could only be observed in H79 metastatic cell line. In addition, PAX-6 repressed the activity directed by the α4 promoter in all cell lines, irrespective of their invasiveness.
The abnormal expression of α4 in the H79 highly invasive cell line may have contributed to its ability to evade the primary tumor and form metastasis. However, our results also suggest that other transcription factors may compete with the binding of PAX-6 to the α4 promoter and thereby contribute to release the PAX-6-mediated repression of α4 in H79.
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