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Characterization in mammalian brain of a DARPP-32 serine kinase identical to casein kinase II
J A Girault1, H C Hemmings, S H Zorn
1Laboratory of Molecular and Cellular Neuroscience, Rockefeller University, New York, New York.
Abstract:
DARPP-32, a dopamine- and cyclic AMP-regulated phosphoprotein of Mr 32,000, is phosphorylated in vitro by casein kinase II at a site which is also phosphorylated in intact cells. In the present study, we show that a protein kinase activity, present in caudate-putamen cytosol, phosphorylates DARPP-32 on a seryl residue located on the same thermolytic peptide that is phosphorylated by purified casein kinase II. This DARPP-32 serine kinase was indistinguishable from casein kinase II on the basis of a number of biochemical criteria. Excitotoxic lesions of the caudate-putamen and immunocytochemistry revealed the presence of casein kinase II in the medium-sized striatonigral neurons which are known to contain DARPP-32. Casein kinase II activity was high in all rat brain regions studied, and casein kinase II-like immunoreactivity was detected in most brain neurons, although some neuronal populations (e.g., cortical pyramidal cells and large striatal neurons) were stained more intensely than others. In rat caudate-putamen, 45% of the total casein kinase II activity was in the cytosol and 20% in the synaptosomal fraction. In mouse cerebral cortex and caudate-putamen, casein kinase II activity was high at embryonic day 16, and remained elevated during development. In addition to DARPP-32, several major substrates for casein kinase II were observed specifically in brain, but not in liver extracts. The high activity of casein kinase II in brain from the embryonic period to adult age and the existence of a number of specific substrates suggest that this enzyme may play an important role in both developing and mature brain, possibly in modulating the responsiveness of target proteins to various extracellular signals.
Insights
Casein kinase II phosphorylates DARPP-32 in the brain, an enzyme crucial for neuronal function. This kinase is abundant in developing and mature brain tissue, suggesting a vital role in neural signaling.
Area of Science:
- Neuroscience
- Molecular Biology
- Biochemistry
Background:
- DARPP-32 is a key phosphoprotein regulated by dopamine and cAMP.
- Casein kinase II (CK2) is known to phosphorylate DARPP-32 in vitro.
- CK2 activity and its substrates are critical in brain function.
Purpose of the Study:
- To identify the specific kinase responsible for DARPP-32 phosphorylation in the caudate-putamen.
- To investigate the distribution and developmental profile of CK2 in the brain.
- To explore the role of CK2 in neuronal signaling.
Main Methods:
- Biochemical characterization of DARPP-32 serine kinase activity in brain cytosol.
- Excitotoxic lesions and immunocytochemistry to determine CK2 localization.
- Assay of CK2 activity in different brain regions and developmental stages.
- Analysis of CK2 substrates in brain and liver extracts.
Main Results:
- A DARPP-32 serine kinase in caudate-putamen cytosol was identified as casein kinase II.
- Casein kinase II is present in medium-sized striatonigral neurons containing DARPP-32.
- CK2 activity is high throughout rat brain regions and during mouse brain development.
- Specific brain CK2 substrates, distinct from liver substrates, were identified.
Conclusions:
- Casein kinase II is the primary enzyme phosphorylating DARPP-32 in the striatum.
- CK2 is widely distributed in the brain and plays a significant role in both developing and mature neurons.
- The enzyme likely modulates neuronal responsiveness to extracellular signals.