The class II Histone deacetylase (HDAC), HDAC4, is expressed in a tissue-specific manner, and it represses differentiation of specific cell types. We demonstrate here that HDAC4 is expressed in the proliferative zone in small intestine and colon and that its expression is down-regulated during intestinal differentiation in vivo and in vitro. Subcellular localization studies demonstrated HDAC4 expression was predominantly nuclear in proliferating HCT116 cells and relocalized to the cytoplasm after cell cycle arrest. Down-regulating HDAC4 expression by small interfering RNA (siRNA) in HCT116 cells induced growth inhibition and apoptosis in vitro, reduced xenograft tumor growth, and increased p21 transcription. Conversely, overexpression of HDAC4 repressed p21 promoter activity. p21 was likely a direct target of HDAC4, because HDAC4 down-regulation increased p21 mRNA when protein synthesis was inhibited by cycloheximide. The importance of p21 repression in HDAC4-mediated growth promotion was demonstrated by the failure of HDAC4 down-regulation to induce growth arrest in HCT116 p21-null cells. HDAC4 down-regulation failed to induce p21 when Sp1 was functionally inhibited by mithramycin or siRNA-mediated down-regulation. HDAC4 expression overlapped with that of Sp1, and a physical interaction was demonstrated by coimmunoprecipitation. Chromatin immunoprecipitation (ChIP) and sequential ChIP analyses demonstrated Sp1-dependent binding of HDAC4 to the proximal p21 promoter, likely directed through the HDAC4 -HDAC3-N-CoR/SMRT corepressor complex. Consistent with increased transcription, HDAC4 or SMRT down-regulation resulted in increased histone H3 acetylation at the proximal p21 promoter locus. These studies identify HDAC4 as a novel regulator of colon cell proliferation through repression of p21. INTRODUCTIONThe acetylation of lysine residues in histones, and/or of transcription factors, is an important posttranslational mechanism of transcriptional regulation (Peterson and Laniel, 2004). Histone deacetylases (HDACs) catalyze the deacetylation of histone and nonhistone substrates, and in general act to repress transcription as part of larger corepressor complexes (Glozak et al., 2005;Yang and Gregoire, 2005). Eighteen mammalian HDACs have been identified to date, and they are grouped into four classes based on their respective homology to yeast deacetylases (Bolden et al., 2006). The class II HDACs can be further subdivided into class IIa (HDAC4, and class , based on the presence in class IIa members of conserved motifs in the N-terminal domain, and extended C terminal tails, that are essential in regulating their function (Yang and Gregoire, 2005).HDACs have emerged as critical regulators of cell growth, differentiation, and apoptotic programs (Bolden et al., 2006). A large body of literature indicates that HDAC inhibitors induce cell cycle arrest, differentiation, and apoptosis in colon cancer cell lines in vitro (Heerdt et al., 1994;Mariadason et al., 1997;Archer et al., 1998;Litvak et al., 1998;Mariadason et al.,...

Background: The neutropenic diet (ND) is prescribed to avoid introduction of bacteria into a host's gastrointestinal tract and reduce infection. Due to a lack of evidence to support the ND, there continues to be debate among pediatric oncologists regarding its usefulness. This prospective randomized controlled trial evaluated the difference in neutropenic infection rates in pediatric oncology patients randomized to Food and Drug Administration approved food safety guidelines (FSGs) versus the ND plus FSGs during one cycle of chemotherapy.Procedure: Pediatric patients receiving cancer treatment with myelosuppressive chemotherapy were eligible. Neutropenic infection was the primary outcome and defined as (i) fever with neutropenia or (ii) hospital admission and treatment for clinical infection and neutropenia. The rate of neutropenic infection was compared with Student's t-test for independent samples. Documented infections were identified by comprehensive chart review and compared between groups using a 2 test.Results: : One hundred fifty patients were randomly assigned to FSGs (n = 73) or ND + FSGs (n = 77). The most common diagnoses were acute lymphoblastic leukemia (32%) and sarcoma (32%).There was no significant difference between the groups in the percentage of patients who developed neutropenic infection: FSGs 33% versus ND + FSGs 35% (P = 0.78). Patients randomized to ND + FSGs reported that following the diet required more effort than those on FSGs alone. Conclusion:The ND offers no benefit over FSGs in the prevention of infection in pediatric oncology patients undergoing myelosuppressive chemotherapy and adherence requires more effort for patients and families. Institutions caring for children with cancer should consider replacing ND guidelines with FSGs. K E Y W O R D Schemotherapy, febrile neutropenia, infections in immunocompromised hosts, nutrition, pediatric hematology/oncology

Surgical biopsy of DIPGs is technically feasible, associated with acceptable risks, and can provide biologic data that can inform treatment decisions.

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