Proteomics of uveal melanomas suggests HSP-27 as a possible surrogate marker of chromosome 3 loss

Low-to-negative HSP-27 protein expression in uveal melanoma correlates strongly with monosomy 3. Further validation is necessary to determine whether immunohistochemical assessment of HSP-27 expression correlates with metastatic mortality.

Frozen specimens from three uveal melanomas with disomy 3 and from four tumors with monosomy 3, according to fluorescence in situ hybridization (FISH) analysis, were subjected to high-resolution, two-dimensional (2-D) gel electrophoresis. The protein expression profiles of the two uveal melanoma cytogenetic groups were compared: Proteins that differed significantly were excised and analyzed by tandem mass spectrometry. Differentially expressed proteins were further analyzed with Western blot analysis. An independent cohort of 41 formalin-fixed, paraffin-embedded (FFPE) uveal melanomas, whose chromosome 3 status had been determined by multiplex ligation-dependent probe amplification (MLPA), was examined for the appropriate antigens by immunohistochemistry.

To compare the proteomic profiles of primary uveal melanomas, with and without loss of chromosome 3.

Four protein spots were 1.5-fold (Student's t-test, P < 0.05) differentially expressed in the two uveal melanoma types: two spots were overexpressed in the disomy 3 group compared with the monosomy 3 group, whereas two spots were underexpressed. Identification of the four spots yielded nine proteins. Western blot analysis confirmed the results for heat shock protein (HSP)-27, vimentin, and pyruvate dehydrogenase beta (PDHB), with a statistical significance for the first two proteins. HSP-27 was significantly downregulated, whereas vimentin was upregulated in the monosomy 3 tumors (Student's t-test, P = 0.003 and P = 0.005, respectively). Immunohistochemistry confirmed low-to-negative HSP-27 protein expression in monosomy 3 uveal melanomas (Student's t-test; P = 0.011). Conclusions: Low-to-negative HSP-27 protein expression in uveal melanoma correlates strongly with monosomy 3. Further validation is necessary to determine whether immunohistochemical assessment of HSP-27 expression correlates with metastatic mortality.