q 2001 International Society for Neurochemistry, Journal of Neurochemistry, 78, 1153±1161 1153 Journal of Neurochemistry, 2001, 78, 1153±1161 The caspase-derived C-terminal fragment of bAPP induces caspase-independent toxicity and triggers selective increase of Ab42 in mammalian cells Ce Âcile Dumanchin-Njock,* Cristine Alves da Costa,* Luc Mercken,² Laurent Pradier² and Fre Âde Âric Checler * *Institut de Pharmacologie Mole Âculaire et Cellulaire, CNRS, Universite  de Nice-Sophia Antipolis, Valbonne, France ²Aventis Pharma, Quai Jules Guesde, Vitry sur Seine, France Abstract During its physiopathological maturation, the b-amyloid precursor protein undergoes several distinct proteolytic events by activities called secretases. In Alzheimer's disease, the main histological hallmark called senile plaque is clearly linked to the overproduction of the amyloid peptides Ab40 and Ab42, two highly aggregable bAPP-derived fragments generated by combined cleavages by b- and g-secretases. Recently, an alternative hydrolytic pathway was described, involving another category of proteolytic activities called caspases, responsible for the production of a 31 amino acids bAPP C-terminal fragment called C31. C31 was reported to lower the viability of N2a cells but the exact mechanisms mediating C31-toxicity remained to be established. Here we show that the transient transfection of pSV2 vector encoding C31 lowers by about 80% TSM1 neuronal cells viability. Arguing against a C31-stimulated apoptotic response, we demonstrate by combined enzymatic and immunological approaches that C31 expression did not modulate basal or staurosporine- induced caspase 3-like activity and pro-caspase-3 activation. Furthermore, C31 did not modify Bax and p53 expressions, poly-(ADP-ribose)-polymerase cleavage and cytochrome c translocation into the cytosol. However, we established that C31 overexpression triggers selective increase of Ab42 but not Ab40 production by HEK293 cells expressing wild-type bAPP751. Altogether, our data demonstrate that C31 induces a caspase-independent toxicity in TSM1 neurons and potenti- ates the pathogenic bAPP maturation pathway by increasing selectively Ab42 species in wild type-bAPP-expressing human cells. Keywords: Alzheimer's disease, amyloid, b-amyloid pre- cursor protein, caspases, HEK293 cells TSM1 neurons. J. Neurochem. (2001) 78, 1153±1161. One of the main histological hallmarks observed in Alzheimer's disease-affected brains is senile plaque (for a review see Selkoe 1997), an extracellular deposit mainly composed of a set of highly insoluble peptides of various lengths (39±43 amino acids) referred to as b-amyloid peptides (Ab). These peptides derive from the combined action of b- and g-secretases, two sets of enzymes responsible for the generation of the N- and C-termini of Ab, respectively (for a review see Haass and Selkoe 1993; Checler 1995; Maury 1995; Octave 1995). Small amounts of Ab could be physiologically produced by various cell types, but the exacerbation of the b/g-secretases-mediated `amy- loidogenic pathway' likely contributes to the complex etiology of Alzheimer's disease (Hardy and Higgins 1992). Recently, an alternative bAPP-hydrolysing pathway was reported that involves another set of activities called caspases (Barnes et al. 1998; Gervais et al. 1999; LeBlanc et al. 1999; Pellegrini et al. 1999; Weidemann et al. 1999; Lu et al. 2000). Caspases belong to a still growing family of thiol proteases involved at various stages in the programmed cell death (for a review see Schwartz and Milligan 1996; Patel et al. 1996). Several studies independently demon- strated that bAPP was proteolysed at its C-terminal cytoplasmic domain (Gervais et al. 1999; Pellegrini et al. Received April 19, 2001; revised manuscript received June 25, 2001; accepted June 29, 2001. Address correspondence and reprint requests to Fre Âde Âric Checler, IPMC du CNRS, UMR6097, 660 Route des Lucioles, 06560, Valbonne, France. E-mail: checler@ipmc.cnrs.fr Abbreviations used:Ab, b-amyloid peptides; PARP, poly-(ADP- ribose)-polymerase; PI, propidium iodide.