Abnormal regulation of high affinity nicotinic receptors in subjects with schizophrenia.

Previous studies have suggested that an abnormality in neuronal nicotinic acetylcholine receptor expression or function may be involved in the neuropathophysiology of schizophrenia. [(3)H]-nicotine and [(3)H]-epibatidine binding were compared in postmortem brain from control and schizophrenic subjects with varying smoking histories. In control subjects, increased receptor binding was seen in hippocampus, cortex, and caudate with increasing tobacco use. In contrast, schizophrenic smokers had reduced nicotinic receptor levels in these brain regions compared to control smokers. Chronic haloperidol and nicotine treatment, in the rat, was used to assess neuroleptic effects on receptor up-regulation by nicotine. A significant increase in cortical nicotinic receptors was seen in both nicotine treated as well as haloperidol and nicotine co-treated animals, suggesting that the abnormal regulation of high affinity neuronal nicotinic receptors in schizophrenics following nicotine use was not related to chronic neuroleptic treatment.

N-terminal domain of Gpa1 (G protein alpha) subunit) is sufficient for plasma membrane targeting in yeast Saccharomyces cerevisiae.

G proteins play a central role in transmitting signals from cell surface receptors to effector proteins inside the cell. Signaling can only occur, however, if all these protein components are properly assembled and localized at the plasma membrane. Past studies have shown that certain segments within the N-terminal region of the G protein alpha subunit are necessary for membrane attachment. Here we identify a region within the yeast G alpha (Gpa1) that is sufficient for membrane attachment, as well as for specific targeting to the plasma membrane. Initially, we constructed chimeric proteins that replace the N terminus of mammalian Gsalpha with the corresponding sequence from Gpa1. Gsalpha is inefficiently targeted to the yeast plasma membrane and therefore cannot fully complement the loss of Gpa1. Gpa1-Gsaplha chimeras were assayed for proper membrane localization by functional complementation of a gpa1Delta ;) mutant, and by sucrose density gradient fractionation of cell membranes. Most of the chimeras tested, including one with only the N-terminal 7 amino acids from Gpa1, exhibited normal membrane targeting and complementing activity. We also fused various lengths of N-terminal Gpa1 sequence to glutathione-S-transferase (GST), a heterologous protein normally expressed in the cytoplasm. The first 67- 36- or 9-amino acids of Gpa1 were all sufficient to direct GST specifically to the plasma membrane in yeast. This analysis defines the extreme N terminus of Gpa1 as the primary determinant of proper membrane targeting, and represents an essential step towards isolating and identifying G protein-targeting proteins within the plasma membrane.

Regulation of G protein signalling in yeast.

A common property of cell signaling systems is the ability to adapt to chronic stimulation. A genetic analysis of receptor/G protein signaling in yeast has led to the identification of a new class of regulators of G protein signaling (RGS proteins), as well as to new insights about the regulatory role of G protein modifications (myristoylation, palmitoylation). Similar modes of regulation are now known to exist in humans. These discoveries fill some important gaps in our understanding of signal transduction, and provide an instructive example of how model organisms, like yeast, can provide new insights relevant to signal regulation in higher eukaryotes.