Identification of NSF as a beta-arrestin1-binding protein. Implications for beta2-adrenergic receptor regulation.

Previous studies have demonstrated that beta-arrestin1 serves to target G protein-coupled receptors for internalization via clathrin-coated pits and that its endocytic function is regulated by dephosphorylation at the plasma membrane. Using the yeast two-hybrid system, we have identified a novel beta-arrestin1-binding protein, NSF (N-ethylmaleimide-sensitive fusion protein), an ATPase essential for many intracellular transport reactions. We demonstrate that purified recombinant beta-arrestin1 and NSF interact in vitro and that these proteins can be coimmunoprecipitated from cells. beta-Arrestin1-NSF complex formation exhibits a conformational dependence with beta-arrestin1 preferentially interacting with the ATP bound form of NSF. In contrast to the beta-arrestin1-clathrin interaction, however, the phosphorylation state of beta-arrestin1 does not affect NSF binding. Functionally, overexpression of NSF in HEK 293 cells significantly enhances agonist-mediated beta2-adrenergic receptor (beta2-AR) internalization. Furthermore, when coexpressed with a beta-arrestin1 mutant (betaarr1S412D) that mimics a constitutively phosphorylated form of beta-arrestin1 and that acts as a dominant negative with regards to beta2-AR internalization, NSF rescues the betaarr1S412D-mediated inhibition of beta2-AR internalization. The demonstration of beta-arrestin1-NSF complex formation and the functional consequences of NSF overexpression suggest a hitherto unappreciated role for NSF in facilitating clathrin coat-mediated G protein-coupled receptor internalization.

The presence of loose anagen hairs obtained by hair pull in the normal population.

To help determine the specificity of "loose anagen" (LA) hairs in Loose Anagen Syndrome, the presence or absence of LA hairs on a gentle but firm hair pull was evaluated in 110 normal subjects from a 0.5 to 83 y old. In children < or =10 y old, 61% had LA hairs on hair pull evaluation and 73% of all hairs obtained were LA hairs. In contrast, LA hairs were found in only two of 87 (2%) normal postpubescent subjects. The number of LA hairs was small in normal children (1-2 per hair pull) and a maximum of one out of every 6-7 hair pulls in adults, far less than that reported with Loose Anagen Syndrome. Although the mere presence of LA hairs on a hair pull test is thus not specific for LAS in children, the number per hair pull may have diagnostic significance. Correlation of these findings with the various hair disorder phenotypes currently termed Loose Anagen Syndrome will be important.