Abstract
Purpose: :
. Proteomic analyses of class I and class 2 uveal melanoma intraocular tumors were pursued for insights into mechanisms of metastasis from class 1 to class 2 and for the identification of biomarkers to detect those at high risk of metastasis.
Methods: :
. Tumor specimens were collected from the eyes of uveal melanoma patients undergoing enucleation. Bruch’s membrane choroid tissues were isolated from normal human control postmortem eyes. Proteins were extracted from the tissues in SDS, digested with trypsin, and peptides were labeled with iTRAQ tags. A pooled control sample was prepared from equal amounts of 9 control digests labeled with the same iTRAQ tag. Fifteen tumor digests were combined individually with the pooled control sample (100 µg each) and fractionated by strong cation exchange chromatography. Proteins were identified by LC MS/MS using a Mascot search engine and the Swiss-Protein sequence database. Relative protein quantification from iTRAQ labeling utilized code written in the statistical program R. Bioinformatic pathway analysis was performed with Ingenuity Pathways Analysis 5.0.
Results: :
. Relative protein quantitation has been obtained from 11 class I and 4 class 2 uveal melanoma tumors. The LC MS/MS analyses yielded quantification of 1685 proteins by two or more unique peptides per protein, including1637 proteins from class 1 and 1100 proteins from class 2 tissues. Six proteins from class 1 and 2 from class 2 tumors were quantified in ≥ 3 donor tissues with average ratios ≥ 2 SD above the mean, including macrophage migration inhibitory factor in class 1. Fifty-eight proteins from class 1 and 15 from class 2 were quantified in ≥ 3 donor tissues with ratios ≥ 2 SD below the mean, including A-kinase anchor protein 12 in class 2. TIMP3 was also of very low abundance in both class 1 and class 2 uveal melanoma.
Conclusions: :
. Elevated levels of macrophage migration inhibitory factor in uveal melanoma is consistent with findings from other studies as is decreased amounts of TIMP3 (2007 Br J Ophthmol 91,1385). Proteomic comparisons of class 1 and class 2 uveal melanoma suggest possible biomarkers of metastasis.
Keywords: proteomics • tumors • melanoma