Quantitative Proteomics of SPPL2c overexpressing HEK cells

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Signal peptide peptidase-like 2c (SPPL2c) is the only member of the GxGD type intramembrane-cleaving aspartyl proteases that so far has not been assigned any substrates and thus its capability of proteolysis and its physiological function remain enigmatic. Based on a surprisingly high expression of SPPL2c in elongated spermatids we applied proteomics on a cellular model system with ectopic expression of SPPL2c and identified a variety of candidate substrates. The majority of these candidate substrates clusters to the biological process of vesicular trafficking. Analysis of selected SNARE proteins reveals proteolytic processing by SPPL2c that impairs vesicular transport and causes retention of cargo proteins in the endoplasmic reticulum. As a consequence, the integrity of subcellular compartments, in particular the Golgi, is disturbed. This may be the trigger for the compartmental reorganization observed during spermatogenesis, which finally results in loss of the majority of endoplasmic reticulum, Golgi and parts of the cytosol in the mature sperm.