| Abstract |
Nicastrin acts as a key regulator for presenilin (PS)-mediated gamma-secretase cleavage of beta-amyloid precursor protein by forming a functional complex with PS1 and PS2. Both TNF-alpha and IL-1, aberrantly produced by activated microglia and astrocytes, play a role in amyloidogenesis and neurodegeneration in the brains of Alzheimer's disease (AD) patients, while BDNF synthesized chiefly by neurons has been found to be substantially reduced in AD brains. To investigate the constitutive and cytokine/neurotrophic factor-regulated expression of nicastrin in human neural cells, its mRNA levels were studied by RT-PCR and northern blot analysis in SK-N-SH neuroblastoma cells, IMR-32 neuroblastoma cells, U-373MG astrocytoma cells, and NTera2 teratocarcinoma-derived differentiated neurons (NTera2-N) following exposure to TNF-alpha, IL-1beta, BDNF, dibutyryl cyclic AMP, or phorbol 12-myristate 13-acetate. Nicastrin mRNA expression was identified in all human neural and nonneural cell lines and tissues examined. The levels of nicastrin mRNA, however, were unaltered in SK-N-SH, IMR-32, U-373MG, and NTera2-N cells by exposure to the factors tested, and unchanged in NTera2 cells during retinoic acid-induced neuronal differentiation. These results indicate that nicastrin mRNA is expressed constitutively in human neural cell lines, where its expression is not regulated at the transcriptional level by a battery of cytokines and growth/differentiation factors which are supposed to be involved in amyloidogenesis, neurodegeneration or neuroprotection in AD brains.
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