Molecular Cloning and Characterization of the Human Glycogen Synthase Kinase-3β Promoter

Abstract

Glycogen synthase kinase 3β (GSK-3β) is a proline-directed kinase that forms part of the wingless signaling pathway. Recent studies have shown that GSK-3β phosphorylates the microtubule-associated protein tau in vitro and in cell culture. Tau is the principal component of the paired helical filaments (PHFs) found in the brains of patients with Alzheimer disease, and PHF-tau is hyperphosphorylated. GSK-3β is therefore one of the candidate kinases for phosphorylating tau in Alzheimer disease. GSK-3β activity is negatively regulated by phosphorylation on serine 9 and positively regulated by phosphorylation on tyrosine 216. However, since overexpression of GSK-3β by transfection leads to increased activity in the absence of any stimuli, GSK-3β activity may also be regulated at the transcriptional level. Indeed, increased GSK-3β protein levels are found in Alzheimer disease brains, and GSK-3β is found associated with PHFs in Alzheimer disease. To understand how GSK-3β activity may be regulated at the transcriptional level, we have isolated the human GSK-3β promoter. The GSK-3β promoter does not contain a conventional TATA box although several other transcription factor binding sites were identified. A putative transcription start site was mapped by 5′ RACE. Transfection of various GSK-3β promoter CAT reporter genes into both COS-7 cells and SHSY5Y neuronal cells revealed that the GSK-3β promoter is more active in neuronal cells. Such transfection studies involving promoter deletion mutants revealed that a negative transcriptional response element may be present at position −1421 to −1363 and an activator sequence at position −427 to −384. CP2 binding sites were also present within the promoter. CP2 has recently been shown to interact with the Alzheimer disease amyloid precursor protein binding protein Fe65. The significance of these results with respect to Alzheimer disease pathogenesis are discussed.