Transcriptional activation of the myogenin gene by MEF2-mediated recruitment of myf5 is inhibited by adenovirus E1A protein.

The basic helix-loop-helix (bHLH) transcription factor myogenin plays a crucial role in terminal differentiation of committed myoblasts into mature myocytes. Transcriptional activation of the myogenin gene requires coordinate action of myocyte enhancer factor 2 (MEF2) proteins and the myogenic bHLH regulators, MyoD or Myf5. Here we show that transcription of the myogenin gene in differentiated cells correlates with MEF2 and NF1 binding to their cognate sites in the proximal myogenin promoter but not with binding of Myf5 or MyoD to the E-box. The importance of MEF2 activity was further demonstrated by expression of antisense MEF2 RNA which repressed MEF2 and Myf5-mediated MEF2 site-dependent reporter gene activation and the synergistic transactivation of a myogenin CAT reporter by Myf5 and MEF2. Adenovirus E1A which has previously been shown to specifically interfere with myogenin gene transcription also inhibited the cooperative transactivation by Myf5/MEF2 and MEF2. Consistently, coimmunoprecipitation studies revealed impaired MEF2/Myf5 protein-protein interactions. These results support a model of transcriptional activation and stabilization of myogenin expression in which DNA-bound MEF2 recruits myogenic bHLH factors into an active but E1A-sensitive transcription factor complex.

A novel E1A domain mediates skeletal-muscle-specific enhancer repression independently of pRB and p300 binding.

The adenovirus E1A oncoprotein completely blocks muscle differentiation and specifically inhibits the transactivating function of myogenic basic helix-loop-helix (bHLH) transcription factors. This inhibition is dependent on the conserved region CR1 of E1A, which also constitutes part of the binding sites for the pocket proteins pRB, p107, and p130 and the transcriptional coactivators p300 and CBP. Here we report a detailed mutational analysis of E1A and the identification of a muscle inhibition motif within CR1. This motif encompasses amino acids 38 to 62 and inhibits Myf-5- or MyoD-mediated activation of myogenin and the muscle creatine kinase gene. Overexpression of this E1A region also inhibits the conversion of 10T1/2 fibroblasts to the myogenic lineage. The sequence motif EPDNEE (amino acids 55 to 60) within CR1 appears to be particularly important, because point mutations of this sequence diminish the E1A inhibitory activity. Interactions of E1A with pRB and with p300 do not seem to be necessary for the muscle-specific enhancer repression, because E1A mutants which lack these interactions still inhibit Myf-5- and MyoD-mediated transactivation. Moreover, overexpression of p300 fails to overcome muscle-specific inhibition by wild-type E1A and mutant E1A protein which lacks pRB binding. Since we have no evidence for direct E1A interaction with bHLH proteins, we propose that E1A may target a necessary cofactor of the muscle-specific bHLH transcription complex.

Acetylsalicylic acid--reocclusion--prophylaxis after angioplasty (ARPA-study). A randomized double-blind trial of two different dosages of ASA in patients with peripheral occlusive arterial disease.

We report on a randomized controlled clinical trial in patients with peripheral occlusive arterial disease who have been successfully treated with angioplasty. The efficacy and the rate of side effects of two doses of ASA (300 mg vs. 1000 mg daily) have been compared during a treatment period of 6 months after angioplasty. It was planned to include a total of 600 patients in the trial. A predefined interim analysis of 200 patients which was performed after the actual inclusion of 218 patients showed identical reocclusions rates and a very similar frequency of side effects in both treatment groups. The study was then terminated since it was not expected that further continuation would lead to a relevant difference between the two treatment groups concerning efficacy or side effects. Patients already included in the trial at the interim evaluation were included in the final analysis, leading to a total number of 223 patients. Finally 112 patients had been randomized to receive a daily dose of 300 mg ASA and 111 patients to receive 1000 mg ASA. Reocclusions occurred in 18 patients (16%) on 300 mg of ASA/day and in 20 patients (18%) receiving 1000 mg ASA/day. The study was interrupted because of side effects in 27 patients (24%) in the 300 mg/day group and in 27 patients (24%) in the 1000 mg/day group. Mostly subjective gastric complaints were the cause of interruption in 17 patients (15%) in the 300 mg group and in 21 patients (19%) receiving the higher dose regimen. So the reocclusion rate was identical in both dosage-groups.(ABSTRACT TRUNCATED AT 250 WORDS)

[Angioblastic sarcoma after mastectomy (author's transl)]. / Angioblastisches Sarkom nach Mastektomie. Fallbeschreibung.

A case of Stewart-Treves-syndrome is presented in which the sarcoma appeared seven years after mastectomy and irradiation.

Experiments to vaccinate marmoset monkeys against malignant lymphoma.

Humoral antibodies can be induced in cotton topped (CT) marmosets with killed Herpesvirus saimiri (HVS) vaccines. The serum antibodies delayed, but did not prevent, malignant lymphoma in actively and passively immunized monkeys after inoculation with 10(3.8)TCID50 of cell-free HVS. Experiments are in progress to determine whether the vaccines are able to protect against smaller challenge dosages of HVS. The immunized monkeys were not resistant against transplantation of tumor cells. Infection with Epstein-Barr virus (EBV) and Marek's disease virus (MDV) did not protect against the tumors caused by superinfection with HVS. Attenuation of HVS was not achieved by passaging the HVS genome through different monkey species.