In cancer cells, the retinoblastoma tumor suppressor RB is directly inactivated by mutation in the RB gene or functionally inhibited by abnormal activation of cyclin-dependent kinase activity. While variations in RB levels may also provide an important means of controlling RB function in both normal and cancer cells, little is known about the mechanisms regulating RB transcription. Here we show that members of the RB and E2F families bind directly to the RB promoter. To investigate how the RB/E2F pathway may regulate Rb transcription, we generated reporter mice carrying an eGFP transgene inserted into a bacterial artificial chromosome containing most of the Rb gene. Expression of eGFP largely parallels that of Rb in transgenic embryos and adult mice. Using these reporter mice and mutant alleles for Rb, p107, and p130, we found that RB family members modulate Rb transcription in specific cell populations in vivo and in culture. Interestingly, while Rb is a target of the RB/E2F pathway in mouse and human cells, Rb expression does not strictly correlate with the cell cycle status of these cells. These experiments identify novel regulatory feedback mechanisms within the RB pathway in mammalian cells.The RB tumor suppressor gene was first identified through its direct mutation or deletion in human retinoblastoma. The RB protein is thought to function largely as a transcriptional cofactor that can repress or potentiate the functions of numerous transcription factors, affecting the expression of a broad number of target genes. Since its initial discovery, RB function has been demonstrated to be inactivated in virtually all human cancers through a variety of mechanisms. In particular, in addition to direct mutation events in the RB gene, the RB protein is often functionally inactivated by phosphorylation in tumor cells with constitutive activation of cyclin/Cdk complexes (44,55). RB inactivation through reduced transcription may also participate in the development of cancer (4, 41); surprisingly, however, little is known about the mechanisms regulating RB transcription in normal and tumor cells.Interestingly, the RB promoter contains a conserved binding site for the E2F transcription factors, some of which are direct partners of RB and key downstream mediators of RB (9). Increasing evidence suggests that this site may contribute to the regulation of RB transcription. For instance, overexpression of E2F1 can activate RB transcription, which may contribute to the variations in RB mRNA levels during cell cycle progression that are observed in some contexts (30, 43) but not in others (5,13,20). In addition, methylation of the E2F site in the RB promoter is sufficient to recruit repressor complexes to inhibit RB transcription (15). Accordingly, reporter assays show that mutation of the E2F site in the RB promoter leads to an absence of RB repression (33). Furthermore, mutation of the E2F (and Sp1) sites in the mouse Rb promoter in transgenic mice has revealed the importance of these sites for Rb expression in vivo (1).Togeth...

Acute and chronic exposure to opioids has been associated with hyperalgesia in both animals and humans. A genetic analysis of opioid-induced hyperalgesia in mice linked the β(2)-adrenergic receptor to mechanical sensitization after opioid exposure. In humans, expansion of the area of mechanical hyperalgesia surrounding an experimentally induced lesion after the cessation of remifentanil infusion is a commonly used model of opioid hyperalgesia (remifentanil-induced postinfusion hyperalgesia, RPH). The purpose of our translational study was to test the hypothesis that the β-adrenergic receptor antagonist propranolol modulates the expression of RPH in humans. This double-blinded, randomized, placebo-controlled, crossover study was performed in 10 healthy human volunteers. During test sessions, intracutaneous electrical stimulation was used to generate areas of secondary mechanical hyperalgesia. The area of this sensitization was measured before, during, and after remifentanil infusion. Heat pain sensitivity was also followed. During one test session, subjects received propranolol infusion. We observed an average increase in the areas of secondary mechanical hyperalgesia to 141% of the baseline in subjects infused with remifentanil and placebo (P=0.00040). However, when remifentanil infusion was combined with propranolol, the area of secondary hyperalgesia after terminating remifentanil was not significantly different than the area before beginning the opioid infusion (P=0.13). Thermal hyperalgesia was not observed after remifentanil infusion. Propranolol infusion at the selected dose had minor hemodynamic effects. Concomitant infusion of propranolol with remifentanil prevented the expression of RPH. β-adrenergic receptor blockade may be a useful pharmacological strategy for preventing hyperalgesia in patients exposed to opioids.

As residents work disparate schedules at multiple locations and because of workweek hour limits mandated by the ACGME, residents may be unable to attend lectures, seminars, or other activities that would enhance their skills. Further, the ACGME requires that residency programs document resident learning in six stated core competencies and provide proof of completion for various other requirements. LMS/LC is a promising technology to provide a means by which residency programs may overcome these obstacles. More studies are needed to show under what conditions an LMS/LC program actually enhances learning, and which elements are most useful to the new generation of learners comfortable with Web 2.0 technologies.

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