Expression of Mutant Epitope-Tagged TACE Constructs in TACE Knockout Fibroblasts and the Importance of TACE Cytoplasmic Domain in PKC-Mediated Phosphorylation
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Alzheimer's disease (AD) is the most common form of dementia affecting the elderly population. It is now known that the major feature of AD is the accumulation of neuritic, amyloid beta (Aβ)-containing plaques and neurofibrillary tangles composed of tau protein. The cleavage of amyloid precursor protein (APP) by β- and γ-secretases (like BACE 1 and presenilin) produces either 40 or 42 amino acid long Aβ product which accumulates in neuronal extracellular space, killing off neurons. On the contrary, there exists a competing pathway to that of β- and γ-secretases in which another secretase, called 𝛼-secretase, cleaves APP within the A/β region and precludes plaque formation in the brain. TACE (TNF-𝛼 Converting Enzyme) is a well known 𝛼-secretase that competes with the AD-causing β- and γ-secretase pathway. Thus, understanding TACE regulation may play an important role in elucidating potential treatments for AD. Recent studies have shown that PKC is directly involved in phosphorylating and activating TACE. In order to determine if the cytoplasrnic dornain of TACE plays a significant role in PKC-mediated activation of TACE, TACE knockout fibroblasts were transfected with wild type and truncated versions of TACE HA constructs and then stimulated with PMA to determine if the truncated version of TACE would reduce the amount of sAPP𝛼 product. We have shown that TACE knockout fibroblasts are transfectable with both TACE HA constructs. Preliminary results also suggest that the truncated version of T ACE lowers sAPP𝛼 cleavage products suggesting that the cytoplasrnic tail of TACE is an important domain responsible for TACE phosphorylation and activation. Future studies will attempt to confirm the observed reaction of sAPP𝛼 in TACE knockout fibroblasts and further verify the role of the cytoplasmic domain in TACE activation as a secretase.