| dc.description | EFhd2 is a calcium binding protein highly expressed in the central
nervous system. Previous studies indicated that EFhd2 is associated to
pathological forms of the microtubule- associated protein tau in JNPL3
tauopathy mouse model and Alzheimer’s disease (AD) patients. EFhd2
is a novel amyloid protein that is overexpressed and co-aggregates with
hyperphosphorylated tau proteins in AD cases. However, the
pathophysiological role of EFhd2 in tau-mediated neurodegeneration is
unknown. Deregulated kinases that lead to the hyperphosphorylation of
tau proteins is an important molecular event in tau-mediated
neurodegeneration, since it facilitates the aggregation of tau proteins.
Known tau kinases associated to neurodegeneration are Cdk5 and
GSK3β. Based on the observation mentioned above, it was
hypothesized that the neurodegeneration process can induce
posttranslational modifications, like phosphorylation, on EFhd2. Our in
vitro phosphorylation assay results demonstrate that Cdk5, but not
GSK3β, phosphorylates EFhd2. Moreover, Cdk5 only phosphorylates
EFhd2 one time. Tandem mass spectrometry analysis identified serine 74
(S74) as the phosphorylation site. A phospho-specific antibody against
EFhd2 phosphorylated at S74 was generated and used to track the
modification in AD postmortem brains. Results demonstrate a significant reduction in the amount of EFhd2 phosphorylated at S74 in AD patients
compared with normal-aging patients. Next, we proceed to evaluate the
effect of the phosphorylation on the association with Tau, formation of
amyloid structures, and the calcium binding activity. No difference was
observed in the association of EFhd2-tau when EFhd2 is phosphorylated
at S74. However, a decrease in the calcium binding activity and a
decrease in the formation of amyloid structures were observed when
EFhd2 is phosphorylated at S74. The results suggest that the
phosphorylation at S74 on EFhd2 is affected during the
neurodegenerative process of AD. Further studies are necessary to
identify the physiological and pathological roles of EFhd2 and the
phosphorylation at S74. | |
