Identification of naturally short gamma-secretase substrates

The intramembrane protease gamma-secretase has broad physiological functions, but also contributes to Notch-dependent tumors and Alzheimer’s disease. To identify naturally short substrates and non-substrates of gamma-secretase, we used four human cell lines of different tissue origins, breast cancer MCF7 cells, cervix carcinoma HeLa cells, T cell leukemia Jurkat cells and lymphoma U937 macrophage-like cells. The cell lines were treated overnight with the established gamma-secretase inhibitor DAPT or DMSO as a control. The proteomes of membrane fractions were determined by nano-liquid chromatography-tandem mass spectrometry and label-free quantitative proteomics. TNFRSF12A, PTPRCAP and C16orf54 were identified as potential naturally short gamma-secretase substrates, whereas other proteins with a short ectodomain including ‘pituitary tumor-transforming gene 1-interacting protein’ (PTTG1IP) did not show an increased abundance upon DAPT treatment.