Astrocytes are the major glial cell within the central nervous system (CNS) and have a number of important physiological properties related to CNS homeostasis. The aspect of astrocyte biology addressed in this review article is the astrocyte as an immunocompetent cell within the brain. The capacity of astrocytes to express class II major histocompatibility complex (MHC) antigens and costimulatory molecules (B7 and CD40) that are critical for antigen presentation and T-cell activation are discussed. The functional role of astrocytes as immune effector cells and how this may influence aspects of inflammation and immune reactivity within the brain follows, emphasizing the involvement of astrocytes in promoting Th2 responses. The ability of astrocytes to produce a wide array of chemokines and cytokines is discussed, with an emphasis on the immunological properties of these mediators. The significance of astrocytic antigen presentation and chemokine/cytokine production to neurological diseases with an immunological component is described.

We have isolated a holoenzyme complex termed BRCC containing BRCA1, BRCA2, and RAD51. BRCC not only displays increased association with p53 following DNA damage but also ubiquitinates p53 in vitro. BRCC36 and BRCC45 are novel components of the complex with sequence homology to a subunit of the signalosome and proteasome complexes. Reconstitution of a recombinant four-subunit complex containing BRCA1/BARD1/BRCC45/BRCC36 revealed an enhanced E3 ligase activity compared to that of BRCA1/BARD1 heterodimer. In vivo, depletion of BRCC36 and BRCC45 by the small interfering RNAs (siRNAs) resulted in increased sensitivity to ionizing radiation and defects in G2/M checkpoint. BRCC36 shows aberrant expression in sporadic breast tumors. These findings identify BRCC as a ubiquitin E3 ligase complex that enhances cellular survival following DNA damage.

Nucleosomal DNA is arranged in a higher-order structure that presents a barrier to most cellular processes involving protein DNA interactions. The cellular machinery involved in sister chromatid cohesion, the cohesin complex, also requires access to the nucleosomal DNA to perform its function in chromosome segregation. The machineries that provide this accessibility are termed chromatin remodelling factors. Here, we report the isolation of a human ISWI (SNF2h)-containing chromatin remodelling complex that encompasses components of the cohesin and NuRD complexes. We show that the hRAD21 subunit of the cohesin complex directly interacts with the ATPase subunit SNF2h. Mapping of hRAD21, SNF2h and Mi2 binding sites by chromatin immunoprecipitation experiments reveals the specific association of these three proteins with human DNA elements containing Alu sequences. We find a correlation between modification of histone tails and association of the SNF2h/cohesin complex with chromatin. Moreover, we show that the association of the cohesin complex with chromatin can be regulated by the state of DNA methylation. Finally, we present evidence pointing to a role for the ATPase activity of SNF2h in the loading of hRAD21 on chromatin.

The Src homology-2 domain containing protein tyrosine phosphatase-2 (SHP2) plays a pivotal role in growth factor and cytokine signaling. Gain-of-function SHP2 mutations are associated with Noonan syndrome, various kinds of leukemias and solid tumors. Thus there is considerable interest in SHP2 as a potential target for anti-cancer and anti-leukemia therapy. We report a salicylic acidbased combinatorial library approach aimed to bind both active site and unique nearby sub-pockets for enhanced affinity and selectivity. Screening of the library led to the identification of a SHP2 inhibitor II-B08 (compound 9) with highly efficacious cellular activity. Compound 9 blocks growth factor stimulated ERK1/2 activation and hematopoietic progenitor proliferation, providing supporting evidence that chemical inhibition of SHP2 may be therapeutically useful for anti-cancer and anti-leukemia treatment. X-ray crystallographic analysis of the structure of SHP2 in complex with 9 reveals molecular determinants that can be exploited for the acquisition of more potent and selective SHP2 inhibitors.

Eukaryotic genes are under the control of regulatory complexes acting through chromatin structure to control gene expression. Here we report the identification of a family of multiprotein corepressor complexes that function through modifying chromatin structure to keep genes silent. The polypeptide composition of these complexes has in common a core of two subunits, HDAC1,2 and BHC110, an FAD-binding protein. A candidate X-linked mental retardation gene and the transcription initiation factor II-I (TFII-I) are components of a novel member of this family of complexes. Other subunits of these complexes include polypeptides associated with cancer causing chromosomal translocations. These findings not only delineate a novel class of multiprotein complexes involved in transcriptional repression but also reveal an unanticipated role for TFII-I in transcriptional repression.The genome of eukaryotes is packaged into chromatin, the fundamental unit of which is the nucleosome. The higher order chromatin structure is formed by arrangement of nucleosomes into an array. Such a higher order chromatin structure presents a barrier to cellular processes such as transcription, DNA replication, and DNA repair. Therefore, controlling accessibility to the nucleosomal DNA provides an important regulatory point in these processes (1). One way to modulate nucleosomal structure is through enzymatic modification of histones by acetylation, phosphorylation, or methylation.A number of transcriptional regulatory complexes have been identified that contain histone acetylation or deacetylation activities. It was previously shown that the hyperacetylated chromatin correlates with active genes whereas the repressed genes exhibit a pattern of hypoacetylation (2, 3). This contention was strengthened by the discovery of the association of a number of transcriptional corepressors with histone deacetylation activity. The HDACs 1 identified in mammalian cells can be divided into three classes. Homologs of the yeast protein Rpd3 are members of the Class I HDACs (4, 5). Included in this class are HDAC1, HDAC2, HDAC3, and HDAC8. Members of the Class II HDACs include HDAC4, HDAC5, HDAC6, HDAC7, HDAC9, and HDAC10. These HDACs appear to be more similar to yeast protein Hda1 (6 -9). A third class of HDACs exists, which unlike the other classes of HDACs, requires an NAD cofactor for activity. The members of this class are homologs of the yeast Sir2 protein (10 -12).Previous biochemical analysis revealed the association of transcriptional corepressor Sin3 with a multiprotein complex containing histone deacetylase activity (13)(14)(15). This complex was shown to contain HDAC1,2 and act as a transcriptional corepressor for a number of DNA-binding repressors including Mad, the nuclear hormone receptors, and the RE1-binding silencer protein, REST (also called NRSF) (14, 16 -19). In addition, a number of groups reported the isolation and characterization of a complex termed NuRD (also NURD and NRD) that not only contains histone deacetylases 1 and 2 but also a DNA...