Tadatoshi Kinouchi

Conventional protein kinase C (PKC)-α and novel PKCε, but not -δ, increase the secretion of an N-terminal fragment of Alzheimer's disease amyloid precursor protein from PKC cDNA transfected 3Y1 fibroblasts

A large soluble N‐terminal fragment of Alzheimers disease amyloid precursor protein (secreted form of APP: APPs) is produced by constitutive processing in the middle of the amyloid β‐protein portion of APP. Recent studies indicate that the activation of endogenous protein kinase C (PKC) with phorbol ester raises the rate of secretion of APPs. We constructed rat fibroblast 3Y1 cells that stably overexpress PKC isoenzymes α, δ, or ε, and analyzed the amount of APPs released from these PKC transfectants. The levels of APPs released from 3Y1 cells overexpressing PKCα and ‐ε were higher than those from PKCδ‐transfected and control cells expressing vector only. These results suggest that specific isoforms of PKC regulate the secretion of APPs through a signaling pathway.

Amyloid precursor protein is found in lysosomes.

The major component of Alzheimers disease amyloid is a small polypeptide referred as the amyloid beta protein, which is derived from a larger precursor, amyloid precursor protein (APP). Cell fractionation and immunological studies on the APP molecule indicate that APP is localized either in the neuron and astrocyte and that the molecule is recovered from lysosomal fraction.

Isolation of an androgen-inducible novel lipocalin gene, Arg1, from androgen-dependent mouse mammary Shionogi carcinoma cells☆

Here we report isolation of an androgen-regulated novel gene from an androgen-dependent mouse mammary Shionogi carcinoma SC-3 cell line. Using a polymerase chain reaction-based subtraction method and Northern blotting analysis, we isolated four androgen-inducible genes from SC-3 cells. Nucleotide sequencings identified three of the genes as cyclin D1, beta-catenin, and fatty acid synthase, respectively, but the fourth, a gene tentatively named as Arg1 (androgen-regulated gene 1), remained undefined. The cloned 2.0-kb sized Arg1 cDNA encoded 414 amino acid sequences. The deduced amino acid sequences, sharing about 30% homology with cathepsin family members at a protein level, had relatively conserved residues around the three proteinase active sites reported earlier. In Northern blotting, Arg1 mRNA was found in kidney, heart, lung, and to a lesser degree, in spleen and liver. Its transcripts were also detected in male reproductive organs on RT-PCR. In addition, its expression levels in prostate were markedly reduced after castration. Unexpectedly, Arg1-expressing COS1 cells showed no significant proteinase activity to various synthesized substrates under neutral or acidic conditions in this study. This might have been due to the replacement of the cysteinyl active site for proteinase to serine residue in the Arg1 amino acid sequences. Given that Arg1 also contains a lipocaline signature known as a binding motif for small hydrophobic molecules at the center of its amino acid sequences, Arg1 is a lipocalin family gene regulated by androgens in prostate and Shionogi carcinoma cells.

Metabolism of amyloid precursor protein in COS cells transfected with a β-secretase candidate

Thimet oligopeptidase (TOP) is a thiol- andmetallo-dependent peptidase and has been shown to beone of the β-secretase candidates. TOPexpressed in COS cells cleaved amyloid precursorprotein (APP) at the β-secretase site, and wefound a proteolytic product of APP called secretedform of APP by β-secretase (sAPPβ) in theconditioned media. Here we demonstrate thatsAPPβ was increased in conditioned media whenTOP was coexpressed in COS cells with APP and treatedwith an ADAM inhibitor SI-27. In addition, althoughTOP expressed in COS cell was localized at nuclei orGolgi apparatus, it exclusively colocalized at Golgiapparatus when APP was coexpressed with TOP.