Regulation of protein kinase FA (a transmembrane signal of insulin and epidermal growth factor) in the brain

Selective interaction of protein kinase FA/glycogen synthase kinase-3alpha with membrane phospholipids

Previously we reported that the activity of protein kinase FA/glycogen synthase kinase-3alpha (kinase FA/GSK-3alpha) can be detected in several brain membrane fractions. In this report, we examined whether kinase FA/GSK-3alpha can directly interact with membrane phospholipids by using anti-kinase FA/GSK-3alpha antibody as a more specific studying tool. It was found that kinase FA/GSK-3alpha can associate with NaOH-extracted brain membranes and selectively interact with several kinds of reconstituted phospholipid vesicles including phosphatidic acid (PA), phosphatidyl ethanolamine (PE), phosphatidyl inositol (PI), and phosphatidyl serine (PS) vesicles. Increasing ionic strength in the reaction could disrupt the interaction between kinase FA/GSK-3alpha and PA, PI, or PE vesicles but had no effect on the interaction between kinase FA/GSK-3alpha and PS vesicles, indicating that both ionic and non-ionic interactions are involved in this process, respectively. Moreover, both kinase activity and protease sensitivity of kinase FA/GSK-3alpha can be affected profoundly by these phospholipid vesicles and different forms of the kinase can be produced when it binds to distinct types of phospholipid vesicles. Taken together, the results demonstrate a direct interaction of kinase FA/GSK-3alpha with membrane phospholipids and suggest that membrane phospholipids may be directly involved in regulating kinase FA/GSK-3alpha activity.

The regulation and function of protein phosphatases in the brain

Data emerging from a number of different systems indicate that protein phosphatases are highly regulated and potentially responsive to changes in the levels of intracellular second messengers produced by extracellular stimulation. They may therefore be involved in the regulation of many cell functions. The protein phosphatases in the nervous system have not been well studied. However, a number of neuronal-specific regulators (such as DARPP-32 and G-substrate) exist, and brain protein phosphatases appear to have particularly low specific activity, suggesting that neuronal protein phosphatases possess considerable and unique potential for regulation. Several early events following depolarization or receptor activation appear to involve specific dephosphorylations, indicating that regulation of protein phosphatase activity is important for the control of many neuronal functions. This article reviews the current literature concerning the identification, regulation, and function of serine/threonine protein phosphatases in the brain, with particular emphasis on the regulation of the major protein phosphatases, PP1 and PP2A, and their potential roles in modulating neurotransmitter release and postsynaptic responses.

Epidermal growth factor and the nervous system

Various growth factors and their receptors are present in the nervous system. This review focuses on the presence of epidermal growth factor (EGF) and its receptors in the central nervous system (CNS). Evidence indicates that EGF in the CNS is the result of local synthesis, by intrinsic and blood-derived macrophages, glial cells and neurons, and uptake from the peripheral blood through the circumventricular organs and probably also through the blood-brain barrier. Evidence is accumulating suggesting that EGF regulates a variety of CNS functions in a specific manner. EGF influences CNS growth, differentiation and maintenance (actions proposed to promote neural regeneration and cell survival following a variety of insults). EGF also induces neuromodulatory actions, affects the neuroendocrine system, and suppresses food intake and gastric acid secretion. Acute and chronic pathological processes, e.g., various cancers, stimulate the production and release of EGF in various cell systems. Monitoring of EGF by the CNS may participate in several neurological manifestations (e.g., appetite suppression, neuroendocrine alterations) frequently accompanying acute and chronic disease. EGF and transforming growth factor-alpha (TGF-alpha, a factor that binds to the EGF receptor with high affinity and induces the same biological signals as EGF) also may be involved in the promotion of malignancy in the CNS and in the neuropathogenesis of degenerative disorders. Thus evidence is accumulating concerning the neurophysiological or neuropathophysiological significance of EGF in the nervous system.