The presenilin (PS)-dependent gamma-secretase activity refers to a high molecular mass-complex including, besides PSI or PS2, three other proteins recently identified, namely nicastrin Aph-1, and Pen-2. This proteolytic complex has been shown to contribute to both gamma- and c-cleavages of the beta-amyloid precursor protein (beta APP), thereby generating beta-amyloid peptides (AP) and the APP intracellular domain (AICD), respectively. TMP21, a member of the p24 cargo protein family, was recently shown to interact with PS complexes. Interestingly, TMP21 modulates gamma-secretase-inediated A beta production but does not regulate F.-secretase-derived AICD formation [F. Chen, H. Hasegawa, G. Schmitt-ulms, T. Kawarai, C. Bohm, T. Katayama, Y. GLI, N. Sanjo, M. Glista, E. Rogaeva, Y. Wakutami, R. Pardossi-Piquard, X. Ruan, A. Tandon, F. Checler, P. Marambaud, K. Hansen, D. Westaway, P. St. George-Hyslop, P. Fraser, TMP21 is a presenilin complex component that modulates gamma- but not epsilon-secretase activities, Nature 440 (2006) 1208-1212]. Here we investigate the functional incidence of the over-expression OF depletion of TMP21 on both intracellular and secreted A beta recoveries and AICD-associated phenotypes. First we confirm that TMP21 depletion yields increased levels of secreted A beta 40. However, we demonstrate that both staurosporine-stimulated caspase-3 activation, p53 and neprilysin expression and activity were not affected by TMP21 over-expression or depletion, Overall, our functional data further reinforce the view that TMP21 behaves as a regulator of gamma- but not epsilon-cleavages generated by PS-dependent gamma-secretase complex. (c) 2008 Elsevier Inc. All rights reserved.