Necrotizing Enterocolitis (NEC) and the Risk of Intestinal Stricture: The Value of C-Reactive Protein

Necrotizing enterocolitis (NEC) is a severe complication frequently seen during the neonatal period associated with high mortality rate and severe and prolonged morbidity including Post-NEC intestinal stricture. The aim of this study is to define the incidence and risk factors of these post-NEC strictures, in order to better orient their medicosurgical care. Sixty cases of NEC were retrospectively reviewed from a single tertiary center with identical treatment protocols throughout the period under study, including systematic X-ray contrast study. This study reports a high rate of post-NEC intestinal stricture (n = 27/48; 57% of survivors), either in cases treated surgically (91%) and after the medical treatment of NEC (47%). A colonic localization of the strictures was more frequent in medically-treated patients than in those with NEC treated surgically (87% vs. 50%). The length of the strictures was significantly shorter in case of NEC treated medically. No deaths were attributable to the presence of post-NEC stricture. The mean hospitalization time in NICU and the median age at discontinuation of parenteral nutrition were longer in the group with stricture, but this difference was not significant. The median age at discharge was significantly higher in the group with stricture (p = 0.02). The occurrence of post-NEC stricture was significantly associated with the presence of parietal signs of inflammation and thrombopenia (<100 000 platelets/mm³). The mean maximum CRP concentration during acute phase was significantly higher in infants who developed stricture (p<0.001), as was the mean duration of the elevation of CRP levels (p<0.001). The negative predictive value of CRP levels continually <10 mg/dL for the appearance of stricture was 100% in our study. In conclusion, this retrospective and monocentric study demonstrates the correlation between the intensity of the inflammatory syndrome and the risk of secondary intestinal stricture, when systematic contrast study is performed following NEC.     

The Eukaryotic Mismatch Recognition Complexes Track with the Replisome during DNA Synthesis

During replication, mismatch repair proteins recognize and repair mispaired bases that escape the proofreading activity of DNA polymerase. In this work, we tested the model that the eukaryotic mismatch recognition complex tracks with the advancing replisome. Using yeast, we examined the dynamics during replication of the leading strand polymerase Polε using Pol2 and the eukaryotic mismatch recognition complex using Msh2, the invariant protein involved in mismatch recognition. Specifically, we synchronized cells and processed samples using chromatin immunoprecipitation combined with custom DNA tiling arrays (ChIP-chip). The Polε signal was not detectable in G1, but was observed at active origins and replicating DNA throughout S-phase. The Polε signal provided the resolution to track origin firing timing and efficiencies as well as replisome progression rates. By detecting Polε and Msh2 dynamics within the same strain, we established that the mismatch recognition complex binds origins and spreads to adjacent regions with the replisome. In mismatch repair defective PCNA mutants, we observed that Msh2 binds to regions of replicating DNA, but the distribution and dynamics are altered, suggesting that PCNA is not the sole determinant for the mismatch recognition complex association with replicating regions, but may influence the dynamics of movement. Using biochemical and genomic methods, we provide evidence that both MutS complexes are in the vicinity of the replisome to efficiently repair the entire spectrum of mutations during replication. Our data supports the model that the proximity of MutSα/β to the replisome for the efficient repair of the newly synthesized strand before chromatin reassembles.     

PP2A: more than a reset switch to activate pRB proteins during the cell cycle and in response to signaling cues

In their active hypophosphorylated state, members of the retinoblastoma family of pocket proteins negatively regulate cell cycle progression at least in part by repressing expression of E2F-dependent genes. Mitogen-dependent activation of G1 and G1/S Cyclin Dependent Kinases (CDKs) results in coordinated hyperphosphorylation and inactivation of these proteins, which no longer bind and repress E2Fs. S and G2/M CDKs maintain pocket protein hyperphosphorylated through the end of mitosis. The inactivating action of inducible CDKs is opposed by the Ser/Thr protein phosphatases PP2A and PP1. Various trimeric PP2A holoenzymes have been implicated in dephosphorylation of pocket proteins in response to specific cellular signals and stresses or as part of an equilibrium with CDKs throughout the cell cycle. PP1 has specifically been implicated in dephosphorylation of pRB in late mitosis and early G1. This review is particularly focused on the emerging role of PP2A as a major hub for integration of growth suppressor signals that require rapid inactivation of pocket proteins. Of note, activation of particular PP2A holoenzymes triggers differential activation of pocket proteins in the presence of active CDKs.