Proteomic Profile of Epithelioid Sarcoma

Epithelioid sarcoma (ES) is a rare soft tissue sarcoma affecting young adults. It is a slow-growing tumor with a high rate of recurrence and metastasis to lymph nodes. Although deletion of the tumor suppressor gene, SMARCB1/ INI1, has been identified in ES, the molecular background factors are largely unknown. To clarify the molecular aberrations contributing to the malignant features of ES, we investigated the proteins present in ES tumor tissues. Two-dimensional difference gel electrophoresis of homogenized tissue samples revealed 3363 protein spots, of which 91 showed differences in intensity between tumor and adjacent non-tumor tissues in eight ES cases. Using mass spectrometry, we characterized 69 unique proteins corresponding to these protein spots. We found that the complex histology of ES was obstacle for the investigation of molecular backgrounds of ES. For instance, although the higher expression of CAPZB in tumor tissues was confirmed by Western blotting, the immunohistochemistry did not determine the specific localize CAPZB in tumor cells. Our study demonstrated the possible utility of proteomic study, and at the same time the difficult aspect of proteomics using homogenized tissue samples.