Stimulation of the human RAD51 nucleofilament restricts HIV-1 integration in vitro and in infected cells.

Stable HIV-1 replication requires the DNA repair of the integration locus catalyzed by cellular factors. The human RAD51 (hRAD51) protein plays a major role in homologous recombination (HR) DNA repair and was previously shown to interact with HIV-1 integrase (IN) and inhibit its activity. Here we determined the molecular mechanism of inhibition of IN. Our standard in vitro integration assays performed under various conditions promoting or inhibiting hRAD51 activity demonstrated that the formation of an active hRAD51 nucleofilament is required for optimal inhibition involving an IN-DNA complex dissociation mechanism. Furthermore we show that this inhibition mechanism can be promoted in HIV-1-infected cells by chemical stimulation of the endogenous hRAD51 protein. This hRAD51 stimulation induced both an enhancement of the endogenous DNA repair process and the inhibition of the integration step. Elucidation of this molecular mechanism leading to the restriction of viral proliferation paves the way to a new concept of antiretroviral therapy based on the enhancement of endogenous hRAD51 recombination activity and highlights the functional interaction between HIV-1 IN and hRAD51.

Chromosomal integration of LTR-flanked DNA in yeast expressing HIV-1 integrase: down regulation by RAD51.

HIV-1 integrase (IN) is the key enzyme catalyzing the proviral DNA integration step. Although the enzyme catalyzes the integration step accurately in vitro, whether IN is sufficient for in vivo integration and how it interacts with the cellular machinery remains unclear. We set up a yeast cellular integration system where integrase was expressed as the sole HIV-1 protein and targeted the chromosomes. In this simple eukaryotic model, integrase is necessary and sufficient for the insertion of a DNA containing viral LTRs into the genome, thereby allowing the study of the isolated integration step independently of other viral mechanisms. Furthermore, the yeast system was used to identify cellular mechanisms involved in the integration step and allowed us to show the role of homologous recombination systems. We demonstrated physical interactions between HIV-1 IN and RAD51 protein and showed that HIV-1 integrase activity could be inhibited both in the cell and in vitro by RAD51 protein. Our data allowed the identification of RAD51 as a novel in vitro IN cofactor able to down regulate the activity of this retroviral enzyme, thereby acting as a potential cellular restriction factor to HIV infection.

Combined occurrence of chyloperitoneum and chylothorax after surgery and chemotherapy for Wilms' tumor.

Chyloperitoneum is an extremely rare complication of abdominal surgery in children and a combined occurrence of chylothorax and chyloperitoneum after abdominal surgery has never been reported in children. Chylous ascites usually occurs as a result of operative trauma to the thoracic duct, cisterna chyli, or its tributaries. About one third of all patients with chylous ascites after retroperitoneal lymph node dissection also develop secondary chylothorax. Diaphragmatic defects have been shown to be responsible for the occurrence of chylothorax secondary to chyloperitoneum. Congenital diaphragmatic weakness may result in evagination of the peritoneum causing diaphragmatic blebs, the rupture of which results in the movement of the peritoneal fluid into the pleural cavity. In the authors' patient, the rent in the diaphragm that occurred during surgery was probably responsible for the chylothorax. The role of chemotherapy, if any, in the pathophysiology of this complication is unknown. Total parenteral nutrition (TPN) is a simple and effective treatment for postoperative chylous effusions. Surgical treatments such as abdominal exploration for the repair of leaking lymphatics and peritoneovenous shunt should be reserved for patients who fail TPN.

Liver abscess caused by Clostridium bifermentans following blunt abdominal trauma.

A case of hepatic abscess and subsequent septicemia caused by Clostridium bifermentans is described. The abscess manifested itself on the third day after blunt trauma to the torso. The patient had nausea, vomiting, fever, evidence of hepatic dysfunction, and subphrenic gas. This case illustrates the association of hepatic abscess and blunt trauma to the torso.

Hypercalcemia in childhood renal tumors.

Hypercalcemia is an uncommon complication of childhood renal tumors. It is exclusively seen in infants 6 months of age or younger with malignant rhabdoid tumor of the kidney (MRTK) or congenital mesoblastic nephroma (CMN). Secretion of parathormone or prostaglandin E2 by the tumor cells is responsible for the hypercalcemia in most of these patients. Bone metastasis has been notably absent in these patients, and the hypercalcemia completely resolves with the removal of the tumor. Hypercalcemia in itself probably does not have any prognostic significance; however, it may serve as a tumor marker in some patients. Early recognition and effective management of this complication may prevent the acute life-threatening as well as the longstanding complications of this serious metabolic disorder.

Presacral mesenchymoma: a case report.

A 4-year-old girl with a presacral benign mesenchymoma is reported. The nature of the tumor was not recognized preoperatively or intraoperatively. There was evidence of pericapsular infiltration of the soft tissues of the pelvis but not signs of malignancy. A follow-up examination after 3 months indicates that the patient has no clinical evidence of recurrence. Review of the English literature shows the rarity of benign mesenchymoma in childhood and the lack of reports of its occurrence in the pelvis.

A new ambulatory system for extended esophageal pH monitoring.

A new 24-h ambulatory esophageal pH monitoring system (AMBI 24) was evaluated in 72 pediatric patients with suspected gastroesophageal reflux (GER). Forty-seven of these patients were monitored at home and the other 25 in our hospital. This system was employed without complication in infants and a full range of pediatric patients, as well as in older children with severe psychomotor delay. The data obtained were consistent with those reported utilizing standard monitoring equipment, and the results served as the basis for subsequent medical management. The results of this study, therefore, suggest that this method of esophageal pH monitoring is a safe and effective means of evaluating GER while allowing for patient mobility.

Colonic variceal bleeding in a child.

A 5-year-old girl with biliary atresia is described who developed lower gastrointestinal bleeding from colonic varices. Vasopressin infusions temporarily controlled the bleeding. Following a right hemicolectomy the bleeding has not recurred.

Noninvasive cardiopulmonary monitoring.

Contrast dilution curves have been utilized for evaluation of hemodynamic function. Noninvasive techniques for this purpose usually have been qualitative, expensive, and cumbersome with minimal applicability to the newborn infant. The technique of roentgen densitometry has been utilized to screen children with heart murmurs. Characteristic curve patterns were identified for normal subjects and for patients with shunts with correlation to catheterization data. This technique is now being applied in a quantitative fashion to estimate cardiac output and left-to-right ductal shunts. Cardiac output volumes were inversely proportional to the difference of the second moments of the dilution curves obtained--the second moment being a measurement of the peak dispersion. The estimation of the percent of left-to-right shunt is related to the exponential decay of the left-sided curve.