Abstract
Purpose: :
The Lysyl Oxidase (LOX) protein is a marker of poor prognosis in several malignancies and is hypothesized to promote a migratory phenotype in hypoxic breast carcinomas. The expression of LOX in human uveal melanoma (UM) cell lines and in 19 cases of choroidal melanomas was examined. LOX expression was also assessed in an in vitro system of tumor hypoxia. The effect of beta-aminoproprionitrile (βAPN), a LOX catalytic inhibitor, on the proliferation and invasion of UM cell lines was also examined.
Methods: :
Four human uveal melanoma cell lines (92.1, SP6.5, MKT-BR, OCM-1), one transformed melanocytic cell line (UW-1), and 19 cases of choroidal melanoma were stained using immunohistochemistry against LOX. Likewise, ten matching choroidal melanomas were stained for the HIF1- protein. UM cell lines were treated with 100 µM of Cobalt Chloride (CoCl2), a hypoxia mimic, and changes in LOX expression were assessed using qPCR. UM cell lines were then treated with βAPN ranging in concentration from 1mM to 1nM and changes in cellular proliferation were measured using a Sulforhodamine-B assay kit. Changes in cellular invasiveness were measured using a Matrigel Invasion Assay following treatment with 750 µM of βAPN.
Results: :
Immunocytochemistry confirmed the expression of LOX in all 5 cell lines. Fourteen of nineteen cases stained positive for LOX with staining intensity varying from high (1/14) to intermediate (5/14) to mild (8/14). In all cases, staining was confined to the cytoplasm of malignant cells. Identical LOX and HIF1- staining intensity was observed in the same samples. Treatment with CoCl2 induced a highly significant increase in LOX mRNA expression. No alteration in cellular proliferation was observed at any treatment dose of βAPN; however, a significant reduction (37%) in cellular invasion was observed at the 750 µM dosage.
Conclusions: :
LOX is expressed in human UM cell lines and in the majority of choroidal melanomas examined. LOX expression appears to be up regulated in response to tumor hypoxia. Treatment with βAPN had no significant effect on cellular proliferation but resulted in a significant reduction in cellular invasiveness. These findings suggest that LOX acts as a metastasis promoting gene in uveal melanoma. Further studies are required to determine LOX’s value as a prognostic marker or therapeutic target in this particular tumor.
Keywords: oncology • pathology: experimental • hypoxia