Fig 1: Treatment of human neuroblastoma SK-N-SH (ATCC HTB-11) cell line with selected TAT1 derivatives resulted in significant augmentation of the proteasome activity. Left: After 24 h treatment with vehicle (DMSO) or TAT compound, cell lysates were prepared and ChT-L activity measured. Relative activity per mg of protein in lysates is presented. Treatment of the same cell lysates with 1 µM Bortezomib lead to almost complete abrogation of ChT-L activity independent of the type of TAT peptide used. Proliferation and viability of cells were not affected by the treatments: live cell counts remained at the level of 95%–107% of control, with the sole exception of a lower count for (9) (86%, non-significant difference). The content of dead cells varied between 9% and 12% for all samples (no significant differences). Right: SK-N-SH cells were treated for four or 24 h with 0.5 or 1.0 µM of (5) and processed as above. An increase of proteasome activity was dose dependent and was affected by the treatment interval. Exposure of the cell lysates to 1 µM BZ almost completely eliminated ChT-L activity and its dependence on treatment time and the applied (5) dose. The control 100% activity corresponded to 1.1 (24 h treatments) or 0.31 (4 h treatments) nanomol of the AMC product released by mg of the lysate per minute. *, p ≤ 0.05; **, p < 0.01; ***, p < 0.001; #, p < 0.00001 (t test; n = 3–4); ns - not significant difference.