Glucose-6-phosphate dehydrogenase (G6PD), the ratelimiting enzyme of the oxidative pentose phosphate cycle, regulates the NADPH/NADP ؉ ratio in eukaryotic cells. G6PD deficiency is one of the most common mutations in humans and is known to cause health problems for hundreds of millions worldwide. Although it is known that decreased G6PD functionality can result in increased susceptibility to oxidative stress, the molecular targets of this stress are not known. Using a Chinese hamster ovary G6PD-null mutant, we previously demonstrated that exposure to a thiol-specific oxidant, hydroxyethyldisulfide, caused enhanced radiation sensitivity and an inability to repair DNA double strand breaks. We now demonstrate a molecular mechanism for these observations: the direct inhibition of DNA end binding activity of the Ku heterodimer, a DNA repair protein, by oxidation of its cysteine residues. Inhibition of Ku DNA end binding was found to be reversible by treatment of the nuclear extract with dithiothreitol, suggesting that the homeostatic regulation of reduced cysteine residues in Ku is a critical function of G6PD and the oxidative pentose cycle. In summary, we have discovered a new layer of DNA damage repair, that of the functional maintenance of repair proteins themselves. In view of the rapidly escalating number of roles ascribed to Ku, these results may have widespread ramifications.
The authors have developed a hand-held gamma-detecting probe (GDP) for intraoperative use that improves the sensitivity of external radioimmunodetection. Radiolabeled monoclonal antibody (MAb) B72.3 was injected in six patients with primary colorectal cancer and 31 patients with recurrent colorectal cancer an average of 16 days preoperatively. The GDP localized the MAb B72.3 in 83 percent of sites. The technique, known as a radioimmunoguided surgery (RIGS) system did not alter the surgical procedure in patients with primary colorectal cancer but did alter the approach in 26 percent (8/31) of patients with recurrent colorectal cancer. Two patients avoided unnecessary liver resections and two underwent extraabdominal approaches to document their disease. The RIGS system may influence the short-term morbidity and mortality of surgery for colorectal cancer. Larger series and longer follow-up are needed to determine whether the RIGS system confers a survival advantage to the patient with colorectal cancer.
This study demonstrates the unique clinical and histologic aspects of fibrolamellar hepatic carcinoma, a rare variant of hepatocellular carcinoma. Three cases are reviewed and an extensive study of immunologic and intracellular substances defining this tumor is presented. Length of survival was considerably longer than typical hepatoma. The cause of death generally is due to a lack of control of the primary tumor. Successful treatment appears to relate to the ability to perform a total excision of the primary hepatic tumor. Chemotherapy should be used only in the presence of metastatic disease. Surgical resection of metastatic disease, unlike the usual hepatocarcinoma, may have some beneficial use. Fibrinogen was found in all tumors. It is possible that this tumor produces fibrinogen to create its unique histologic appearance. Carcinoembryonic antigen is described for the first time in this tumor. Both deposits of alpha-1 antitrypsin and copper were found in most of the tissues studied. The presence and amounts of these substances differ markedly from the common type of hepatoma. This unique composition of intracellular components may both facilitate histologic diagnosis, particularly if the amount of tissue is limited, and give further insight into the etiology of this tumor.
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