N-myristoylation is a common form of co-translational protein fatty acylation resulting from the attachment of myristate to a required N-terminal glycine residue.1,2 We show that aberrantly acquired N-myristoylation of SHOC2, a leucine-rich repeat-containing protein that positively modulates RAS-MAPK signal flow,3–6 underlies a clinically distinctive condition of the neuro-cardio-facial-cutaneous disorders family. Twenty-five subjects with a relatively consistent phenotype previously termed Noonan-like syndrome with loose anagen hair [OMIM 607721]7 shared the 4A>G missense change (Ser2Gly) in SHOC2 that introduces an N-myristoylation site, resulting in aberrant targeting of SHOC2 to the plasma membrane and impaired translocation to the nucleus upon growth factor stimulation. Expression of SHOC2S2G in vitro enhanced MAPK activation in a cell type-specific fashion. Induction of SHOC2S2G in Caenorhabditis elegans engendered protruding vulva, a neomorphic phenotype previously associated with aberrant signaling. These results document the first example of an acquired N-terminal lipid modification of a protein causing human disease.

Controlling the number of functional gamma-aminobutyric acid A (GABA(A)) receptors in neuronal membranes is a crucial factor for the efficacy of inhibitory neurotransmission. Here we describe the direct interaction of GABA(A) receptors with the ubiquitin-like protein Plic-1. Furthermore, Plic-1 is enriched at inhibitory synapses and is associated with subsynaptic membranes. Functionally, Plic-1 facilitates GABA(A) receptor cell surface expression without affecting the rate of receptor internalization. Plic-1 also enhances the stability of intracellular GABA(A) receptor subunits, increasing the number of receptors available for insertion into the plasma membrane. Our study identifies a previously unknown role for Plic-1, a modulation of GABA(A) receptor cell surface number, which suggests that Plic-1 facilitates accumulation of these receptors in dendritic membranes.

GABAA receptor alpha6 subunit gene expression marks cerebellar granule cell maturation. To study this process, we used the Deltaalpha6lacZ mouse line, which has a lacZ reporter inserted into the alpha6 gene. At early stages of postnatal cerebellar development, alpha6-lacZ expression is mosaic; expression starts at postnatal day 5 in lobules 9 and 10, and alpha6-lacZ is switched on inside-out, appearing first in the deepest postmigratory granule cells. We looked for factors regulating this expression in cell culture. Membrane depolarization correlates inversely with alpha6-lacZ expression: granule cells grown in 25 mM [K+]o for 11-15 d do not express the alpha6 gene, whereas cultures grown for the same period in 5 mM [K+]o do. This is influenced by a critical early period: culturing for >/=3 d in 25 mM [K+]o curtails the ability to induce the alpha6 gene on transfer to 5 mM [K+]o. If the cells start in 5 mM [K+]o, however, they still express the alpha6-lacZ gene in 25 mM [K+]o. In contrast to granule cells grown in 5 mM [K+]o, cells cultured in 25 mM [K+]o exhibit no action potentials, mEPSCs, or mIPSCs. In chronic 5 mM [K+]o, factors may therefore be released that induce alpha6. Blockade of ionotropic and metabotropic GABA and glutamate receptors or L-, N-, and P/Q-type Ca2+ channels did not prevent alpha6-lacZ expression, but inhibition of action potentials with tetrodotoxin blocked expression in a subpopulation of cells.