Ewing tumour is characterized by speci®c chromosome translocations which fuse EWS to a subset of genes encoding ETS transcription factors, most frequently FLI-1. We report the analysis of the expression of various cell cycle regulators both in Ewing tumour derived cell lines and in di erent cellular models with either inducible or constitutive EWS-FLI-1 cDNA expression. In Ewing cell lines, cyclin D1, CDK4, Rb, p27 KIP1 and c-Myc were consistently highly expressed whereas p57 KIP2 , p15 INK4B and p14 ARF demonstrated undetectable or low expression levels. The amount of p16 INK4A , p21 CIP1 , p18 INKAC and CDK6 was variable from one cell line to the other. The inducible expression of EWS-FLI-1 led to a strong upregulation of c-Myc and a considerable downregulation of p57 KIP2 . Other proteins did not show evident modi®cation. High c-Myc and very low p57 KIP2 expression levels were also observed in neuroblastoma NGP cells constitutively expressing EWS-FLI-1 as compared to parental cells. Analysis of the p57 KIP2 promoter indicated that EWS-FLI-1 downregulates, possibly through an indirect mechanism, the transcription of this gene. Finally, we show that ectopic expression of p57 KIP2 in Ewing cells blocks proliferation through a complete G1 arrest. These results suggest that the modulation of p57 KIP2 expression by EWS-FLI-1 is a fundamental step in Ewing tumorigenesis. Oncogene (2001) 20, 3258 ± 3265.

The dual-specificity tyrosine phosphorylation-regulated kinase 1A (DYRK1A) gene is located within the Down Syndrome (DS) critical region on chromosome 21 and is implicated in the generation of Tau and amyloid pathologies that are associated with the early onset Alzheimer's Disease (AD) observed in DS. DYRK1A is also found associated with neurofibrillary tangles in sporadic AD and phosphorylates key AD players (Tau, amyloid precursor, protein, etc). Thus, DYRK1A may be an important therapeutic target to modify the course of Tau and amyloid beta (Ab) pathologies. Here, we describe EHT 5372 (methyl 9-(2,4-dichlorophenylamino) thiazolo[5,4-f]quinazoline-2-carbimidate), a novel, highly potent (IC 50 = 0.22 nM) DYRK1A inhibitor with a high degree of selectivity over 339 kinases. Models in which inhibition of DYRK1A by siRNA reduced and DYRK1A over-expression induced Tau phosphorylation or Ab production were used. EHT 5372 inhibits DYRK1A-induced Tau phosphorylation at multiple AD-relevant sites in biochemical and cellular assays. EHT 5372 also normalizes both Ab-induced Tau phosphorylation and DYRK1A-stimulated Ab production. DYRK1A is thus as a key element of Abmediated Tau hyperphosphorylation, which links Tau and amyloid pathologies. EHT 5372 and other compounds in its class warrant in vivo investigation as a novel, high-potential therapy for AD and other Tau opathies.

␤-Amyloid peptides (A␤) that form the senile plaques of Alzheimer disease consist mainly of 40-and 42-amino acid (A␤ 40 and A␤ 42) peptides generated from the cleavage of the amyloid precursor protein (APP). Generation of A␤ involves ␤-secretase and ␥-secretase activities and is regulated by membrane trafficking of the proteins involved in A␤ production. Here we describe a new small molecule, EHT 1864, which blocks the Rac1 signaling pathways. In vitro, EHT 1864 blocks A␤ 40 and A␤ 42 production but does not impact sAPP␣ levels and does not inhibit ␤-secretase. Rather, EHT 1864 modulates APP processing at the level of ␥-secretase to prevent A␤ 40 and A␤ 42 generation. This effect does not result from a direct inhibition of the ␥-secretase activity and is specific for APP cleavage, since EHT 1864 does not affect Notch cleavage. In vivo, EHT 1864 significantly reduces A␤ 40 and A␤ 42 levels in guinea pig brains at a threshold that is compatible with delaying plaque accumulation and/or clearing the existing plaque in brain. EHT 1864 is the first derivative of a new chemical series that consists of candidates for inhibiting A␤ formation in the brain of AD patients. Our findings represent the first pharmacological validation of Rac1 signaling as a target for developing novel therapies for Alzheimer disease. Alzheimer disease (AD)2 is the most common neurodegenerative disorder marked by progressive loss of memory and cognitive ability. The pathology of AD is characterized by the presence of amyloid plaques (1), intracellular neurofibrillary tangles, and pronounced cell death. The ␤-amyloid peptide (A␤) (2) is the main constituent of senile plaques found in AD brains. Furthermore, extracellular A␤ 42 appears toxic to neurons in vitro and in vivo (reviewed in Ref.3). A␤ is generated by proteolysis of an integral membrane protein, the amyloid precursor protein (APP), via at least two post-translational pathways. The amyloidogenic cleavage of APP is a sequential processing of APP initiated by ␤-secretase (BACE), which cleaves APP within the luminal domain or at the cell surface, generating the N terminus of A␤ (4). This cleavage generates several membrane-bound proteolytic C-terminal fragments (CTFs), such as the 99-residue ␤-CTF (also called C99), as well as the secreted APP ectodomain sAPP␤. The C terminus of A␤ is subsequently generated by intramembranous cleavage of CTFs by ␥-secretase, producing either A␤ 40 or A␤ 42. The cleavages at residues 40 -42 are referred to as ␥-cleavage, and the cleavages at residues 49 -52 are referred to as ⑀-cleavage (5). The nonamyloidogenic cleavage of APP, which precludes A␤ generation, is mediated by ␣-secretase, a disintegrin and metalloproteinase 10, and a disintegrin and metalloproteinase 17, in a reaction believed to occur primarily on the plasma membrane. This proteolytic cleavage by ␣-secretase occurs within the A␤ region and produces soluble APP (sAPP␣), the dominant processing product, and the residual membrane-bound 10-kDa CTF (CTF␣, also called C83). Like C99, C83 is a subs...

No abstract