Phosphorylation by Aurora B Converts MgcRacGAP to a RhoGAP during Cytokinesis

AbstractCell division is finely controlled by various molecules including small G proteins and kinases/phosphatases. Among these, Aurora B, RhoA, and the GAP MgcRacGAP have been implicated in cytokinesis, but their underlying mechanisms of action have remained unclear. Here, we show that MgcRacGAP colocalizes with Aurora B and RhoA, but not Rac1/Cdc42, at the midbody. We also report that Aurora B phosphorylates MgcRacGAP on serine residues and that this modification induces latent GAP activity toward RhoA in vitro. Expression of a kinase-defective mutant of Aurora B disrupts cytokinesis and inhibits phosphorylation of MgcRacGAP at Ser387, but not its localization to the midbody. Overexpression of a phosphorylation-deficient MgcRacGAP-S387A mutant, but not phosphorylation-mimic MgcRacGAP-S387D mutant, arrests cytokinesis at a late stage and induces polyploidy. Together, these findings indicate that during cytokinesis, MgcRacGAP, previously known as a GAP for Rac/Cdc42, is functionally converted to a RhoGAP through phosphorylation by Aurora B

Prospective study of the UGT1A1*27 gene polymorphism during irinotecan therapy in patients with lung cancer: Results of Lung Oncology Group in Kyusyu (LOGIK1004B)

Background: Uridine 5′-diphospho-glucuronosyltransferase 1A1 (UGT1A1*27) is known to impair the effect of UGT in basic research; however, little clinical investigation has been conducted. To evaluate the effect of the UGT1A1*27 polymorphism in irinotecan therapy, we conducted a prospective study. Methods: Eligibility criteria included: lung cancer patients; scheduled irinotecan therapy doses of single ? 80, combination ? 50, radiation with single ? 50, or radiation with combination ? 40 mg/m2; age ? 20; and Eastern Cooperative Oncology Group performance score (PS) 0?2. Patients were examined for UGT1A1*28 and *6 polymorphisms and received irinotecan. When the UGT1A1*28 polymorphism was detected, a search for UGT1A1*27 was conducted. Fifty patients were enrolled, with 48 patients determined eligible. Results: UGT1A1 polymorphisms *28/*28, *6/*6, *28/*6, *28/?, *6/?, ?/? observed 0 (0%), 1 (2%), 1 (2%), 7 (15%), 17 (35%) and 22 (46%), respectively. UGT1A1*27 were examined in nine patients including one ineligible patient; however, no polymorphisms were found. The study ceased after interim analysis. In an evaluation of the side effects of irinotecan, patients with UGT1A1*28 and UGT1A1*6 polymorphisms had a higher tendency to experience febrile neutropenia than wild type (25% and 32% vs. 14%). Incidences of grade 3/4 leukopenia and neutropenia were significantly higher in patients with UGT1A1*28 polymorphisms compared with wild type (75% vs. 32%, P = 0.049; 75% vs. 36%, P = 0.039, respectively). Conclusion: Our prospective study did not locate the UGT1A1*27 polymorphism, suggesting that UGT1A1*27 does not significantly predict severe irinotecan toxicity in cancer patients

Prospective study of the UGT1A1*27 gene polymorphism during irinotecan therapy in patients with lung cancer: Results of Lung Oncology Group in Kyusyu (LOGIK1004B)

Abstract Background: Uridine 5 0 -diphospho-glucuronosyltransferase 1A1 (UGT1A1*27) is known to impair the effect of UGT in basic research; however, little clinical investigation has been conducted. To evaluate the effect of the UGT1A1*27 polymorphism in irinotecan therapy, we conducted a prospective study. Methods: Eligibility criteria included: lung cancer patients; scheduled irinotecan therapy doses of single ≥ 80, combination ≥ 50, radiation with single ≥ 50, or radiation with combination ≥ 40 mg/