Amyloid beta-peptide (Abeta), which plays a central role in Alzheimer's disease, is generated by presenilin-dependent gamma-secretase cleavage of beta-amyloid precursor protein (betaAPP). We report that the presenilins (PS1 and PS2) also regulate Abeta degradation. Presenilin-deficient cells fail to degrade Abeta and have drastic reductions in the transcription, expression, and activity of neprilysin, a key Abeta-degrading enzyme. Neprilysin activity and expression are also lowered by gamma-secretase inhibitors and by PS1/PS2 deficiency in mouse brain. Neprilysin activity is restored by transient expression of PS1 or PS2 and by expression of the amyloid intracellular domain (AICD), which is cogenerated with Abeta, during gamma-secretase cleavage of betaAPP. Neprilysin gene promoters are transactivated by AICDs from APP-like proteins (APP, APLP1, and APLP2), but not by Abeta or by the gamma-secretase cleavage products of Notch, N- or E- cadherins. The presenilin-dependent regulation of neprilysin, mediated by AICDs, provides a physiological means to modulate Abeta levels with varying levels of gamma-secretase activity.

Mutations in the PTEN-induced kinase 1 (PINK1) gene have recently been implicated in autosomal recessive early onset Parkinson Disease (1, 2). To investigate the role of PINK1 in neurodegeneration, we designed human and murine neuronal cell lines expressing either wild-type PINK1 or PINK1 bearing a mutation associated with Parkinson Disease. We show that under basal and staurosporine-induced conditions, the number of terminal deoxynucleotidyltransferase-mediated dUTP nick end labeling (TUNEL)-positive cells was lower in wild-type PINK1 expressing SH-SY5Y cells than in mock-transfected cells. This phenotype was due to a PINK1-mediated reduction in cytochrome c release from mitochondria, which prevents subsequent caspase-3 activation. We show that overexpression of wild-type PINK1 strongly reduced both basal and staurosporine-induced caspase 3 activity. Overexpression of wild-type PINK1 also reduced the levels of cleaved caspase-9, caspase-3, caspase-7, and activated poly(ADP-ribose) polymerase under both basal and staurosporine-induced conditions. In contrast, Parkinson disease-related mutations and a kinase-inactive mutation in PINK1 abrogated the protective effect of PINK1. Together, these results suggest that PINK1 reduces the basal neuronal pro-apoptotic activity and protects neurons from staurosporine-induced apoptosis. Loss of this protective function may therefore underlie the degeneration of nigral dopaminergic neurons in patients with PINK1 mutations. Parkinson disease (PD)2 is the most common neurodegenerative movement disorder, affecting ϳ1% of the population by age 65 years (3, 4). It is characterized by the predominant degeneration of midbrain dopaminergic neurons. Although most patients with PD are sporadic, familial cases represent ϳ10% of all diagnoses. To date, six genes responsible for inherited forms of PD have been identified. Mutations in the ␣-synuclein (5), LRRK2 (leucine-rich repeat kinase 2) and UCH-L1 (ubiquitin C-terminal esterase L1) genes cause dominant forms of familial PD. In contrast, mutations in parkin (6), DJ-1 (7,8), and the newly identified PTEN (phosphatase and tensin homologue on chromosome 10)-induced kinase 1 (PINK1) (1, 2) are responsible for recessive forms of familial PD.PINK1 encodes a highly conserved, 581-amino acid, putative serinethreonine protein kinase and is a member of a small family of novel kinases including CLIK1 (CLP-36 interacting kinase)/PDLIM1 kinases. Bioinformatic analysis suggests that residues Gly-193 to Leu-507 comprise the catalytic domain, residues Gly-193 to Lys-219 form the ATPbinding cassette (with Tyr-166 as an autophosphorylated regulatory residue), and residues Asp-384 to Glu-417 form an activation loop (Fig. 1). PINK1 is transcriptionally transactivated by the PTEN gene (9) and is expressed at variable levels in different cancer cell types. Valente et al. showed that overexpressed, epitope-tagged PINK1 localized to mitochondria and may have a protective function against cell death (1).To further investigate the role of PINK1 in neuronal ap...

To investigate the effect of persistent HIV infection on the immune system, we studied leukocyte functions in 14 asymptomatic homosexual men (CDC group Il/III) who were at least two years seropositive, but who still had normal numbers of circulating Cfl4+ T cells. Compared with age-matched heterosexual men and HIV-negative homosexual men, the CD4' and CD8' T cells from seropositive men showed decreased proliferation to anti-CD3 monoclohal antibody and decreased CD4' T-helper activity on PWM-driven differentiation of normal donor B cells. Monocytes of HIV-infected homosexual men showed decreased accessory function on normal T cell proliferation induced by CD3 monoclonal antibody. The most striking defect in leukocyte functional activities was observed in the B cells of HIV-infected men.

We have designed new non-peptidic potential inhibitors of gamma-secretase and examined their ability to prevent production of amyloid-beta 40 (Abeta40) and Abeta42 by human cells expressing wild-type and Swedish-mutant beta-amyloid precursor protein (betaAPP). Here we identify three such agents that markedly reduce recovery of both Abeta40 and Abeta42 produced by both cell lines, and increase that of C99 and C83, the carboxy-terminal fragments of betaAPP that are derived from beta-and alpha-secretase, respectively. Furthermore, we show that these inhibitors do not affect endoproteolysis of endogenous or overexpressed presenilins. These inhibitors are totally unable to affect the mDeltaEnotch-1 cleavage that leads to generation of the Notch intracellular domain (NICD). These represent the first non-peptidic inhibitors that are able to prevent gamma-secretase cleavage of betaAPP without affecting processing of mDeltaEnotch-1 or endoproteolysis of presenilins. The distinction between these two proteolytic events, which are both prevented by disruption of presenilin genes, indicates that although they are intimately linked with betaAPP and Notch maturation, presenilins are probably involved in the control of maturation processes upstream of enzymes that cleave gamma-secretase and Notch.

Autosomal recessive mutations in PINK1 are a rare cause of young-onset Parkinson disease.

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