Identification of novel pRb binding sites using CpG microarrays suggests that E2F recruits pRb to specific genomic sites during S phase.

The retinoblastoma (Rb) tumor suppressor protein is an important regulator of cell proliferation and differentiation. Many studies have shown that pRb can negatively regulate the activity of the E2F family of transcription factors during G(0) and G(1) phases of the cell cycle, perhaps by serving as a bridge between the E2Fs and transcriptional repressors such as histone deacetylases and methylases. However, pRb has also been shown to localize to discrete DNA foci during S phase, a time at which pRb is thought to be dissociated from E2F. Numerous other DNA binding proteins have been shown to interact with pRb, suggesting that pRb may control progression through S phase by binding to sites in the genome distinct from E2F target gene promoters. To test this hypothesis, we have identified novel pRb binding sites within the human genome using an unbiased approach which relies upon a combination of chromatin immunoprecipitation and CpG microarray analysis. To provide the greatest opportunity of finding distinct sets of pRb binding sites, we examined pRb binding in chromatin obtained from human Raji cells synchronized in either G(0)/G(1) phase or S phase. These experiments have allowed us to identify a large set of new genomic binding sites for the pRb protein. We found that some sites are occupied by pRb only during G(0)/G(1) phase, as would be predicted from previous models of pRb function. We also identified sites to which pRb bound only during S phase and other sites which were bound constitutively by pRb. Surprisingly, we found that E2F1 was present at most of the CpG islands bound by pRb, independent of the phase of the cell cycle. Thus, although pRb has the potential to interact with numerous transcription factors, our data suggest that the majority of DNA-bound pRb is recruited to E2F target promoters during both G(0)/G(1) and S phases.

Sedative preference of families for lumbar punctures in children with acute leukemia: propofol alone or propofol and fentanyl.

Propofol is a common sedative/anesthetic used for invasive procedures in children with cancer. The purpose of this study was to determine whether families of children with acute leukemia prefer propofol alone or propofol plus fentanyl for lumbar puncture (LP) sedation. We conducted a randomized, placebo controlled, double blind, crossover study. Each patient was studied twice, once with propofol/placebo and once with propofol/fentanyl. Data collected included the modified Yale Preoperative Anxiety Score (M-YPAS) at baseline and after placebo or fentanyl, Induction Compliance Checklist, recovery excitement, recovery time, and adverse events. After the study, families were asked which sedative regimen they preferred for future LPs. Twenty-two patients received 44 LP sedations: propofol 22, propofol/fentanyl 22. The average age was 6.4+/-4.2 years (mean+/-SD). There were no significant differences between groups in M-YPAS, Induction Compliance Checklist or recovery excitement. Adverse events occurred in 11/22 patients (50%) propofol and 4/22 (18.2%) propofol/fentanyl (P=0.0196). Average recovery time (mean+/-SD) was 36.86+/-17.1 minutes propofol versus 26.36+/-16.4 minutes propofol/fentanyl (P=0.047). Sixteen families (72.7%) chose propofol with fentanyl for future LP sedations (P=0.05). In conclusion, most families prefer propofol and fentanyl for LPs. Propofol with fentanyl was also associated with fewer adverse events and faster recovery.