Co-translational translocation of human sortilin into the ER lumen is inhibited by cyclotriazadisulfonamide

The small molecule cyclotriazadisulfonamide (CADA) was shown to down-modulate the expression of human CD4 in a signal peptide-dependent way, through inhibition of its co-translational translocation across the ER membrane. Previous studies had not yet identified additional substrates and suggested selectivity of CADA for human CD4. We used a PowerBlot western array to screen the proteome of CADA-treated SUP-T1 human CD4+ T lymphocytes and to identify new targets of this compound. Our study revealed that only a small subset of the 444 detected proteins was differentially expressed after treatment with CADA. Validation of candidate protein expression confirmed the CADA-induced up-regulation of the cell cycle progression regulator pRb2 and down-modulation of the transcription factor c-Jun. However, the change in expression of these two proteins did not impact cell cycle transition. Interestingly, the signal peptide-containing membrane protein sortilin was identified as a secondary substrate for CADA. Both cellular expression and in vitro co-translational translocation of sortilin were significantly reduced by CADA, although to a lesser extent as compared to human CD4. As our current proteomic survey detected mainly cytoplasmic proteins, full analysis of the secreted and membrane protein fraction with an unbiased mass spectrometry technique will complement these findings.status: publishe