Adenovirus E4orf3 targets transcriptional intermediary factor 1γ for proteasome-dependent degradation during infection.

The ability of adenovirus early region proteins, E1B-55K and E4orf6, to usurp control of cellular ubiquitin ligases and target proteins for proteasome-dependent degradation during infection is well established. Here we show that the E4 gene product, E4orf3 can, independently of E1B-55K and E4orf6, target the transcriptional corepressor transcriptional intermediary factor 1γ (TIF1γ) for proteasome-mediated degradation during infection. Initial mass spectrometric studies identified TIF1 family members-TIF1α, TIF1ß, and TIF1γ-as E1B-55K-binding proteins in both transformed and infected cells, but analyses revealed that, akin to TIF1α, TIF1γ is reorganized in an E4orf3-dependent manner to promyelocytic leukemia protein-containing nuclear tracks during infection. The use of a number of different adenovirus early region mutants identified the specific and sole requirement for E4orf3 in mediating TIF1γ degradation. Further analyses revealed that TIF1γ is targeted for degradation by a number of divergent human adenoviruses, suggesting that the ability of E4orf3 to regulate TIF1γ expression is evolutionarily conserved. We also determined that E4orf3 does not utilize the Cullin-based ubiquitin ligases, CRL2 and CRL5, or the TIF1α ubiquitin ligase in order to promote TIF1γ degradation. Further studies suggested that TIF1γ possesses antiviral activity and limits adenovirus early and late gene product expression during infection. Indeed, TIF1γ knockdown accelerates the adenovirus-mediated degradation of MRE11, while TIF1γ overexpression delays the adenovirus-mediated degradation of MRE11. Taken together, these studies have identified novel adenovirus targets and have established a new role for the E4orf3 protein during infection.

Adenovirus 12 E4orf6 inhibits ATR activation by promoting TOPBP1 degradation.

Activation of the cellular DNA damage response is detrimental to adenovirus (Ad) infection. Ad has therefore evolved a number of strategies to inhibit ATM- and ATR-dependent signaling pathways during infection. Recent work suggests that the Ad5 E4orf3 protein prevents ATR activation through its ability to mislocalize the MRN complex. Here we provide evidence to indicate that Ad12 has evolved a different strategy from Ad5 to inhibit ATR. We show that Ad12 utilizes a CUL2/RBX1/elongin C-containing ubiquitin ligase to promote the proteasomal degradation of the ATR activator protein topoisomerase-IIbeta-binding protein 1 (TOPBP1). Ad12 also uses this complex to degrade p53 during infection, in contrast to Ad5, which requires a CUL5-based ubiquitin ligase. Although Ad12-mediated degradation of p53 is dependent upon both E1B-55K and E4orf6, Ad12-mediated degradation of TOPBP1 is solely dependent on E4orf6. We propose that Ad12 E4orf6 has two principal activities: to recruit the CUL2-based ubiquitin ligase and to act as substrate receptor for TOPBP1. In support of the idea that Ad12 E4orf6 specifically prevents ATR activation during infection by targeting TOPBP1 for degradation, we demonstrate that Ad12 E4orf6 can inhibit the ATR-dependent phosphorylation of CHK1 in response to replication stress. Taken together, these data provide insights into how Ad modulates ATR signaling pathways during infection.

Encircling reperfusion pattern on the stress-minus-delay bull's-eye map improves sensitivity of myocardial perfusion scans.

BACKGROUND: Myocardial perfusion imaging is subject to considerable noise due to re-registration and attenuation artifact. METHODS: On a retrospective review, we identified 51 studies that showed encircling reperfusion pattern on a stress-minus-delay bull's-eye map with concurrent cardiac catheterization within 4 months. Encircling reperfusion was defined as a band of reversibility > or =2.5 standard deviations above that of the gender-matched and age-matched normal studies. This had to surround the delay defect for at least two-thirds of its circumference on the stress-minus-delay bull's-eye map. Three expert readers, blinded to cardiac catheterization results, individually interpreted myocardial perfusion imaging without and with a stress-minus-delay bull's-eye map. A certainty index of 1-100 (100 being the highest certainty for the presence of perfusion defects) was recorded for image interpretation. RESULTS: The intra-class correlation coefficient between readers indicated a strong agreement. Using encircling reperfusion pattern on a stress-minus-delay bull's-eye map, the mean increase in certainty index scores was 8.0+/-7.30 (P<0.0001). This increase in certainty index scores was associated with a significant increase in sensitivity from 67 to 83% (P=0.01) without any significant decrease in specificity (P=0.16). CONCLUSIONS: The pattern of encircling reperfusion on the stress-minus-delay bull's-eye map can improve the interpreter's confidence and sensitivity without significantly compromising specificity for identifying true myocardial perfusion defects.

Pharmacologic stress myocardial perfusion imaging.

Pharmacologic stress agents (dipyridamole, adenosine and dobutamine) allow virtually all patients to be safely assessed for ischemic heart disease. These agents have mild but significant side effects, mandating a thorough knowledge of indications, contraindications, side effects and management before their use. Adjunctive exercise improves image quality in vasodilator pharmacologic myocardial perfusion imaging. Diabetics, especially women, have a much higher cardiac event rate than nondiabetics for an equal amount of ischemia. They also have a higher incidence of asymptomatic ischemia. There is growing support for screening with myocardial perfusion imaging (MPI) for asymptomatic ischemia in diabetics. The ability of MPI to identify hypocontractile but viable myocardium, thus predicting improvement in myocardial function after revascularization, is one of the most powerful uses of the modality. Vasodilator MPI should be used as the initial test in patients with left bundle branch block or paced ventricular rhythm, even if they are able to exercise.

A case of congenitally corrected transposition of the great arteries with rare but life-threatening ventricular tachycardia and a coincidental single coronary ostium.

Congenitally corrected transposition of the great vessels (CCTGA) is a rare congenital heart defect. Patients with CCTGA have the anatomical right ventricle as their systemic pumping chamber, with ventricular dysfunction and congestive heart failure (CHF) being relatively common in older adults. The most common presenting feature is bradycardia due to high-degree atrioventricular (AV) blocks. Patients with CCTGA are increasingly subject to CHF with advancing age; this complication is extremely common by the fourth decade. The majority of patients have an inverted coronary arterial pattern.1 We report a case of a patient with CCTGA who presented with rare but life-threatening ventricular tachycardia (VT) leading to syncope, with preserved systemic ventricular function. Coincidentally, the patient also had a single coronary ostium.