BAP1 alterations in primary mesothelioma cells. Chromatograms showing BAP1 mutations (A). Arrow in the top panel indicates the location of mutation. NCI-Meso16 cells had a splice site mutation in intron 4 of BAP1. NCI-Meso17 and NCI-Meso21 had frame shift mutations at the intron15/exon16 junction and in exon 13 of BAP1 gene, respectively. Immunohistochemistry (B) showing lack of expression of BAP1 protein in cells with mutant BAP1. Only NCI-Meso19 cells which were BAP1 wild-type expressed the BAP1 protein. Western blot (C) showing the expression of BAP1 in primary mesothelioma cells. For western blot, mesothelioma cell lines NCI-H28 and NCI-H2052 were used as controls for mutant and wild-type BAP1 respectively. A faint BAP1 band was observed for NCI-Meso17 cells, which exhibits a 5-bp deletion in exon 13. Western blot showing (D) the expression of BAP1 in late passage primary mesothelioma cells. The faint BAP1 band which was observed for NCI-Meso17 cells in early passage was absent in late passage.