Cross-talk between Rac1 GTPase and dysregulated Wnt signaling pathway leads to cellular redistribution of beta-catenin and TCF/LEF-mediated transcriptional activation.

Aberrant activation of the Wnt pathway is observed in numerous cancers, and is particularly important in colon cancer. We demonstrate that Rac1 GTPase can significantly increase the signaling activity of beta-catenin in cells with inherent dysregulation of the canonical Wnt signaling pathway. Expression of dominant-negative (N17)Rac1 mutant in colon cancer cells caused a marked inhibition of Wnt signaling, as determined by the TCF/LEF-responsive (TOPFLASH) transcription assay. Expression of a constitutively active (V12)Rac1 mutant caused up to 40-fold induction from the TOPFLASH promoter, and this was dependent on the presence of stabilized beta-catenin. This induction was completely blocked by the expression of dominant-negative TCF-4, suggesting that beta-catenin and TCF-4 complex formation is required for Rac1-mediated transcription. Furthermore, we show that Cyclin D1, an important biological Wnt target gene, is regulated by Rac1 in a beta-catenin/TCF-dependent manner. We observed that Rac1 co-immunoprecipitates with beta-catenin and TCF-4 only in its active GTP-bound form. Both cell fractionation studies and fluorescence microscopy indicate that overexpression of V12Rac1 results in increased cytosolic and nuclear expression of beta-catenin. Interestingly, mutation of the polybasic region of Rac1, which prevents its nuclear localization, also caused an appreciable decrease in nuclear localization of beta-catenin, and effectively abolished its beta-catenin-dependent transcription co-activator function. Taken together, our data demonstrate a novel mechanism of Wnt pathway regulation whereby activation of Rac1 amplifies the signaling activity of stabilized/mutated beta-catenin by promoting its accumulation in the nucleus, and synergizing with beta-catenin to augment TCF/LEF-dependent gene transcription.

Implementation of surgical audit in Pakistan.

UNLABELLED: Surgical audit, while extensively practised in the West, is still widely believed an impossible attainment in developing countries owing to the high cost and technology required to implement it. It is thus a poorly understood and rarely practised exercise in these countries. In this article we attempt to demonstrate the usefulness and feasibility of implementing audit in the setting of a developing country using personal computers (PCs) with simple, inexpensive and easily available software. We discuss the results of data analysis of 18 months of audit conducted by one general surgery team (2 consultants, 4 residents) at the Aga Khan University Hospital, Karachi. OBJECTIVE: To implement surgical audit in the setting of a developing country using microcomputers with simple, inexpensive and easily available software. DESIGN: Data analysis of inpatient audit proformas filled at weekly audit meetings from January 1989-July 1990 using Dbase III Plus. SETTING: One general surgery team (2 consultants, 4 residents) in a tertiary care hospital in Karachi. MAIN OUTCOME MEASURES: Disease patterns, caseload, complication rates. RESULTS: Conditions related to the biliary system made 26.1 per cent of the admitting diagnoses; 25.3 per cent of the patients had some co-existing medical condition as well, diabetes and hypertension being most common. The overall morbidity was 12.3 per cent and the mortality 1.5 per cent. Chest infection, wound infection and urinary retention were the most common post-operative complications. CONCLUSIONS: Results of audit data analysis initiated new research projects and development of protocols to improve patient care. Audit meetings also served as teaching sessions for residents.

Post-operative critical care and outcomes of limb replantation: experience in a developing country.

Replantation is the treatment of choice for traumatic amputation. Its success rates vary, reaching 80% in world's best centres. This study analyses management practices of replantation in a regional centre in a developing country. Out of six replantations, four were successful. The median warm ischaemia time of the severed limb was 4.5h (range 1-13.5) and the median duration of general anaesthesia required for initial surgery was 6.25h (range 4.7-8.0). All patients needed intensive care following replantation for a median of 7 days (range 5-15). Pulse oximetry values were observed to be the same in the graft and the patient in successful cases. Two grafts failed. The median haemoglobin values on the 1st, 3rd and 5th post-operative day were 9.8, 7.0 and 8.4g/dl, respectively. The median platelet counts in the same time periods were 118x10(9), 68x10(9) and 205x10(9)L(-1). The median total fluid intake was 2.2, 3.1 and 3.4ml/kg/h on the 1st, 3rd and 5th post-operative day and the median urine output was 2.4, 2.6 and 2.7ml/kg/h, respectively. The observed post-surgical reduction in platelet count normalised by the 5th post-operative day. Higher fluid intake and lower haemoglobin levels appear to minimise the systemic effects of reperfusion injury, preventing the onset of renal failure and promoting graft perfusion. Pulse oximetry was a useful tool to assess graft perfusion and appear to offer a prognostic value. Three of the above 4 patients were traced for review 5 years later and had functioning grafts.

Extended indications for polypropylene mesh closure of the abdominal wall.

Over a two-year period (1982-1984) polypropylene (Marlex) mesh was used without closing the abdominal wound in 21 patients judged clinically likely to require further abdominal exploration. A total of 43 meshes were implanted. All 21 patients had more than one major laparotomy, median 3 laparotomies (range 2-7) for drainage of pus (76 per cent) and/or intestinal leakage (67 per cent). Definitive abdominal wound closure after removal of polypropylene mesh was either by delayed primary suturing (33 per cent) or consisted of split skin grafting on the granulating wound (24 per cent). Three wounds were left to granulate without skin grafting (14 per cent). Mortality in this group of patients was 29 per cent and no complications resulted directly from implantation of polypropylene mesh. Polypropylene mesh closure of the abdominal wall not only provides simple and rapid access to the abdomen but also allows free drainage and daily inspection for the development of fistulae or the seepage of pus which are indications for further exploration. In that the clinical outcome is relatively favourable in this group of critically ill surgical patients who required multiple laparotomies within a short interval, it is suggested that mesh closure of the abdominal wound is indicated whenever abdominal re-entry is judged probable or rational.

STK11/LKB1 germline mutations are not identified in most Peutz-Jeghers syndrome patients.

Germline mutations of the STK11 gene mapped to chromosome 19p13.3 are responsible for Peutz Jeghers syndrome (PJS), a dominant disorder associated with characteristic gastrointestinal hamartomatous polyps and a predisposition to various cancers. We conducted a detailed investigation of germline STK11 alterations by protein truncation test and genomic DNA sequence analysis in ten unrelated PJS families. We identified a novel truncating deletion spanning STK11 exons 2-7 in a single patient and several known polymorphisms. Loss of heterozygosity studies in PJS polyps of four of these patients identified an allelic deletion of D19S886 in another patient. Our results suggest that STK11 mutations account for only a proportion of PJS cases.