PCL staff identify cleavage site of shed Mesothelin
Mesothelin is a cell-surface tumor-associated antigen that is expressed in several human cancers. The restricted expression of mesothelin on normal tissues and high expression in many cancer cells make it a good target for tumor-specific immunotherapy. Mesothelin is shed from the cell surface and is present in the sera of patients with malignant mesothelioma and could negatively impact the efficacy of these treatments. Dr. Ira Pastan’s Laboratory of Molecular Biology (National Cancer Institute) has investigated the mechanism of the mesothelin shedding. The first step in characterizing this mechanism was to identify the cleavage site. PCL senior scientist Oleg Chertov identified the C-terminus of shed mesothelin by analyzing tryptic peptides by MALDI-TOF MS/MS (see figure below). Further work by Dr. Pastan’s laboratory demonstrated that mesothelin shedding was mediated by a TNF-a converting enzyme. In addition reduction of shedding activity significantly improved the in vitro cytotoxicity of a mesothelin targeted immunotoxin currently in clinical trials. For further information see the link to the Cancer Research article.
The determination of shed mesothelin C-terminal sequence. A, SDS-PAGE profile of shed mesothelin preparations from A431/H9 supernatant and ascites of a patient with mesothelioma. Bands in frame are shed mesothelin and subjected to the sequencing. B, the C-terminal cleavage sites of mesothelin.