Activity-Dependent Phosphorylation of the Transcription Factor Sp4: Role in Development and Disease.
Abstract: The formation of a functional nervous system requires the activity of cell extrinsic cues that promote cell differentiation and development by influencing intrinsic gene expression programs. The transcription factor Sp4 is expressed in neurons where it controls the developmental patterning of dendrites. Alterations of the Sp4 gene have been linked to schizophrenia and bipolar disorder (B... read moreD), and reduced levels of the Sp4 protein have been observed in the postmortem cerebellum of subjects with BD. Previous studies revealed that neuronal activity, in the form of membrane depolarization, regulates Sp4 protein levels by preventing proteasomal degradation. The pathways by which neuronal activity regulates Sp4 activity and protein stability, however, were unknown. In this dissertation, I report the identification of a novel Sp4 regulatory modification, phosphorylation at S770. Glutamate signaling through the N-methyl D-Aspartate (NMDA) receptor, a key excitatory neurotransmitter receptor in the brain that influences neuronal morphology, development, and survival, dephosphorylated Sp4 at S770 through the activation of the PP1/PP2A phosphatase. We have shown that a point mutation that mimics phosphorylation disrupts the Sp4-dependent maturation of cerebellar granule (CG) neuron primary dendrites and may contribute to the regulation of Sp4 protein stability. We generated antiserum that specifically recognizes Sp4 phosphorylation at S770 and, in collaboration, this antiserum was used to examine the levels of Sp4 S770 phosphorylation in the postmortem cerebellum of BD subjects. We found that the ratio of phosphorylated to total Sp4 was increased in BD subjects compared to controls, suggesting that the pathways regulating Sp4 phosphorylation are disrupted in BD. We further show that lithium, a commonly used therapeutic for BD, specifically decreased Sp4 S770 phosphorylation. Collectively, the studies presented here identify a signaling pathway regulating Sp4 phosphorylation and activity to influence dendrite patterning during development. Our finding of increased levels of Sp4 phosphorylation in BD also reveals new insights into the molecular biology underlying this psychiatric disorder.
Thesis (Ph.D.)--Tufts University, 2014.
Submitted to the Dept. of Cell, Molecular & Developmental Biology.
Advisor: Grace Gill.
Committee: Karina Meiri, Michele Jacob, Peter Juo, and Raymond Kelleher.
Keywords: Cellular biology, Neurosciences, and Biochemistry.read less