The CUL1 C-terminal sequence and ROC1 are required for efficient nuclear accumulation, NEDD8 modification, and ubiquitin ligase activity of CUL1

Members of the cullin and RING finger ROC protein families form heterodimeric complexes to constitute a potentially large number of distinct E3 ubiquitin ligases. We report here that the highly conserved C-terminal sequence in CUL1 is dually required, both for nuclear localization and for modification by NEDD8. Disruption of ROC1 binding impaired nuclear accumulation of CUL1 and decreased NEDD8 modification in vivo but had no effect on NEDD8 modification of CUL1 in vitro, suggesting that ROC1 promotes CUL1 nuclear accumulation to facilitate its NEDD8 modification. Disruption of NEDD8 binding had no effect on ROC1 binding, nor did it affect nuclear localization of CUL1, suggesting that nuclear localization and NEDD8 modification of CUL1 are two separable steps, with nuclear import preceding and required for NEDD8 modification. Disrupting NEDD8 modification diminishes the IkappaBalpha ubiquitin ligase activity of CUL1. These results identify a pathway for regulation of CUL1 activity-ROC1 and the CUL1 C-terminal sequence collaboratively mediate nuclear accumulation and NEDD8 modification, facilitating assembly of active CUL1 ubiquitin ligase. This pathway may be commonly utilized for the assembly of other cullin ligases.

Ku recruits the XRCC4-ligase IV complex to DNA ends

Genetic experiments have determined that Ku, XRCC4, and ligase IV are required for repair of double-strand breaks by the end-joining pathway. The last two factors form a tight complex in cells. However, ligase IV is only one of three known mammalian ligases and is intrinsically the least active in intermolecular ligation; thus, the biochemical basis for requiring this ligase has been unclear. We demonstrate here a direct physical interaction between the XRCC4-ligase IV complex and Ku. This interaction is stimulated once Ku binds to DNA ends. Since XRCC4-ligase IV alone has very low DNA binding activity, Ku is required for effective recruitment of this ligase to DNA ends. We further show that this recruitment is critical for efficient end-joining activity in vitro. Preformation of a complex containing Ku and XRCC4-ligase IV increases the initial ligation rate 20-fold, indicating that recruitment of the ligase is an important limiting step in intermolecular ligation. Recruitment by Ku also allows XRCC4-ligase IV to use Ku's high affinity for DNA ends to rapidly locate and ligate ends in an excess of unbroken DNA, a necessity for end joining in cells. These properties are conferred only on ligase IV, because Ku does not similarly interact with the other mammalian ligases. We have therefore defined cell-free conditions that reflect the genetic requirement for ligase IV in cellular end joining and consequently can explain in molecular terms why this factor is required.

High frequency of genetic instability of microsatellites in human prostatic adenocarcinoma

In order to investigate the genomic instability associated with prostate cancer, 36 microsatellite marker loci on chromosomes 1p, 3p, 5q, 8p, 8q, 9p, 11q and 13q were analyzed using microdissected samples from prostate cancer and adjoining microscopically normal tissues from the same slide. DNA was extracted from the normal and tumor cells of 40 microdissected prostate-cancer samples, amplified by PCR, and analyzed for microsatellite instability (MSI) using 36 different polymorphic DNA markers. In the present study, we have utilized a highly refined technique of PCR product separation on a sequencing gel, developed in our laboratory, which clearly shows high-quality results for the microsatellite instability in prostate cancer. The results of this study suggest that 45% (18 out of 40) showed genomic instability at a minimum of 1 locus; 4 cases each showed MSI at one and 2 loci, 4 cases had MSI at 3 loci, 3 cases showed MSI at 5 loci, while one case each showed MSI at 7, 8 and 15 loci. There was no significant correlation between the MSI and stage or grade of the tumors. This extensive study on genomic instability in prostate cancer found the occurrence of MSI to be very high, which suggests a role of MSI in the pathophysiology of prostate cancer.

Deletion of chromosome 11p15, p12, q22, q23-24 loci in human prostate cancer

Loss of heterozygosity (LOH) on chromosome 11 is frequently altered in various epithelial cancers. The present study was designed to investigate LOH on chromosome 11 in microdissected samples of normal prostatic epithelium and invasive carcinoma from the same patients. For this purpose, DNA was extracted from the microdissected normal and tumor cells of 38 prostate cancers, amplified by polymerase chain reaction PCR and analyzed for LOH on chromosome 11 using 9 different polymorphic DNA markers (D11S1307, D11S989, D11S1313, D11S898, D11S940, D11S1818, D11S924, D11S1336 and D11S912). LOH on chromosome 11 was identified in 30 of 38 cases (78%) with at least one marker. Four distinct regions of loss detected were: 1) at 11p15, at loci between D11S1307 and D11S989; 2) at 11p12, on locus D11S131 (11p12); 3) at 11q22, on loci D11S898, D11S940 and D11S1818; and 4) at 11q23-24, on loci between D11S1336 and D11S912. We found 25% of the tumors with LOH at 11p15; 39% had LOH at 11p12; 66% had LOH at 11q22; and 47% had LOH at 11q23-24. These deletions at 11p15, 11p12, 11q22 and 11q23-24 loci were not related to the stage or grade of the tumor.

Chromosome 3p24-26 and 3p22-12 loss in human prostatic adenocarcinoma

Identification of loss of heterozygosity on specific genetic loci is crucial for understanding the pathogenesis of prostate cancer at the molecular level. This is especially important because the deleted regions may contain putative tumor suppressor genes. Chromosome 3p loss appears to be frequently associated with various epithelial cancers. To our knowledge, there is no report on loss of heterozygosity (LOH) of chromosome 3 in human prostate cancer. The present study was designed to investigate the LOH on chromosome 3p in microdissected samples of delineated regions of normal and invasive carcinoma areas of prostatic epithelium from the same tumor sections. For this purpose, DNA was extracted from microdissected normal and tumor cells of 38 prostate cancers, amplified by PCR and analyzed for LOH on chromosome 3p using 6 different polymorphic DNA markers (D3S1560, THRB, D3S647, D3S1298, D3S1228 and D3S1296). Our results suggest that LOH was identified in 34 of 38 cases (89%) with at least one marker. Twelve of 30 informative cases showed LOH at D3S1560; 18 of 22 informative cases showed loss at THRB; 20 of 38 informative cases showed deletion at D3S647; 16 of 38 informative cases showed loss at D3S1298; 12 of 34 informative cases showed LOH at D3S1228; and 6 of 34 informative cases showed LOH at D3S1296 regions. Our results suggest that the LOH is on the 3p24-26 and 3p22-12 regions of the short arm of chromosome 3, indicating 2 discrete areas of deletion on chromosome 3p. The deletion at 3p24-26 and 3p22-12 was not related to the stage or grade of the tumor.

Whither the PRO? Analysis of the effectiveness of three Medicare peer review organizations in a Florida hospital

The objective of this retrospective study was to evaluate the effectiveness of a peer review organization (PRO) on patient mortality rate in a not-for-profit, 988-bed community hospital in Florida. The number of deaths per hospital discharge (mortality) was compared prior to the Professional Foundation for Health Care (PFHC) holding the contract as the Medicare PRO (1983), during two years in which the PRO was fully active (1990 and 1991), during the year limited PRO activities were conducted (1992), and when PRO activities were again fully expanded (1993). All Medicare hospital discharges, including deaths, were included from January through May during 1983, 1990 through 1993. There was no intervention. Patient mortality as a determinant of PRO effectiveness was evaluated prior to the PRO, during a portion of the years the PFHC held the contract as the Medicare PRO, and an identical time period one year later with limited PRO review and again the following year when full reviews returned. The number of deaths did not change significantly. Mandated peer reviews of care to inpatient hospital Medicare beneficiaries did not significantly improve health care as measured by mortality.