Grb4/Nckbeta acts as a nuclear repressor of v-Abl-induced transcription from c-jun/c-fos promoter elements.

Grb4 is an adaptor protein consisting of three src homology (SH) 3 domains and a single SH2 domain. We previously cloned Grb4 as a direct interacting partner of Bcr-Abl and v-Abl via the Grb4 SH2 domain. We now show that overexpression of Grb4 results in significant inhibition of v-Abl-induced transcriptional activation from promitogenic enhancer elements such as activator protein 1 (AP-1) and serum-responsive element (SRE). We demonstrate that the inhibitory activity of Grb4 is independent of the direct interaction of v-Abl and Grb4: a Grb4 mutant that lacks a functional SH2 domain shows an even more pronounced inhibition of AP-1/SRE. Further mutational analysis revealed that the first two SH3 domains primarily mediate the inhibitory function. The inhibitory activity of Grb4 is specific for c-jun/c-fos-regulated promoter elements and is located downstream of MEKK1 and JNK because co-expression of Grb4 resulted in down-regulation of MEKK1-induced AP-1 activity without affecting JNK activity. Thus, the nuclear pool of Grb4 is likely to mediate this inhibition. Indeed, cell fractionation and fluorescence microscopy studies revealed that the stronger inhibitory potential of the Grb4 SH2 mutant occurred in conjunction with increased nuclear localization of this mutant. Our results suggest a novel role for Grb4 in the inhibition of promitogenic enhancer elements such as 12-O-tetradecanoylphorbol-13-acetate-responsive element and SRE.

Comparison of intravenous and oral antibiotic therapy in the treatment of fractures caused by low-velocity gunshots. A prospective, randomized study of infection rates.

One hundred and ninety consecutive patients (222 fractures) who had an extra-articular fracture of a long bone as a result of a low-velocity gunshot were randomized into two groups on the basis of the method of administration of antibiotics. Group 1 consisted of 101 patients (120 fractures) who were managed with intravenous administration of cephapirin sodium and gentamicin for three days. Group 2 comprised eighty-nine patients (102 fractures) who were managed with oral administration of ciprofloxacin for three days. The two groups were comparable in terms of the age of the patient, the locations of the fractures, and the time from the injury to the commencement of antibiotic therapy. Injuries that needed operative débridement or fixation were excluded. All patients were followed until the fracture had healed. Two infections developed in two of the ninety-nine patients (118 fractures) who completed the study in Group 1, and two infections developed in two of the eighty-seven patients (100 fractures) who completed the study in Group 2. With the numbers available, there was no significant difference in the rates of infection (2 per cent for both) between the two groups. All four fractures that were complicated by infection were located in the distal half of the tibia. We concluded that oral and intravenous administration of antibiotics were equally effective for prophylaxis against infection after an extra-articular fracture from a low-velocity gunshot.