The CCAAT binding factor CBF is a heteromeric transcription factor, which binds to functional CCAAT motifs in many eukaryotic promoters. cDNAs for the A and B subunits of CBF (CBF-A and CBF-B) and for their yeast homologues HAP3 and HAP2 have been previously isolated, but the purified recombinant CBF-A and CBF-B together are unable to bind to CCAAT motifs in DNA. Here we report the isolation of a cDNA coding for rat CBF-C, demonstrate that recombinant CBF-C is required together with CBF-A and CBF-B to form a CBF-DNA complex, and show that CBF-C is present in this protein-DNA complex together with the other two subunits. We further show that CBF-C allows formation of a complex between the purified recombinant yeast HAP2 and HAP3 polypeptides and a CCAAT-containing DNA and is present in this complex, implying the existence of a CBF-C homologue in yeast. We show that CBF-A and CBF-C interact with each other to form a CBF-A-CBF-C complex and that CBF-B does not interact with CBF-A or CBF-C individually but that it associates with the CBF-A-CBF-C complex. Our results indicate that CBF is a unique evolutionarily conserved DNA binding protein.

Purpose Morphologically heterogeneous prostate cancers (PC) that behave clinically like small cell PC (SCPC) share their chemotherapy responsiveness. We asked whether these clinically defined, morphologically diverse, ‘aggressive variant PC’ (AVPC) also share molecular features with SCPC. Experimental Design 59 PC samples from 40 clinical trial participants meeting AVPC criteria, and 8 patient-tumor derived xenografts (PDX) from 6 of them, were stained for markers aberrantly expressed in SCPC. DNA from 36 and 8 PDX was analyzed by Oncoscan® for copy number gains (CNG) and losses (CNL). We used the AVPC PDX to expand observations and referenced publicly available data sets to arrive at a candidate molecular signature for the AVPC. Results Irrespective of morphology, Ki67 and Tp53 stained ≥ 10% cells in 80% and 41% of samples respectively. RB1 stained <10% cells in 61% of samples and AR in 36%. MYC (surrogate for 8q) CNG and RB1 CNL showed in 54% of 44 samples each and PTEN CNL in 48%. All but 1 of 8 PDX bore Tp53 missense mutations. RB1 CNL was the strongest discriminator between unselected castration resistant PC (CRPC) and the AVPC. Combined alterations in RB1, Tp53 and/or PTEN were more frequent in the AVPC than in unselected CRPC and in The Cancer Genome Atlas samples. Conclusions Clinically defined AVPC share molecular features with SCPC and are characterized by combined alterations in RB1, Tp53 and/or PTEN.

Four stress-responsive protein kinases, including GCN2 and PKR, phosphorylate eukaryotic translation initiation factor 2␣ (eIF2␣) on Ser51 to regulate general and gene-specific protein synthesis. Phosphorylated eIF2 is an inhibitor of its guanine nucleotide exchange factor, eIF2B. Mutations that block translational regulation were isolated throughout the N-terminal OB-fold domain in Saccharomyces cerevisiae eIF2␣, including those at residues flanking Ser51 and around 20 Å away in the conserved motif K 79 GYID 83 . Any mutation at Glu49 or Asp83 blocked translational regulation; however, only a subset of these mutations impaired Ser51 phosphorylation. Substitution of Ala for Asp83 eliminated phosphorylation by GCN2 and PKR both in vivo and in vitro, establishing the critical contributions of remote residues to kinase-substrate recognition. In contrast, mutations that blocked translational regulation but not Ser51 phosphorylation impaired the binding of eIF2B to phosphorylated eIF2␣. Thus, two structurally distinct effectors of eIF2 function, eIF2␣ kinases and eIF2B, have evolved to recognize the same surface and overlapping determinants on eIF2␣.

We have identified PIAS1 (protein inhibitor of activated STAT-1), -3, -x␣, and -x␤ as SOX9-associated polypeptides using the Gal4-based yeast two-hybrid system and a cDNA library derived from a chondrocytic cell line. These PIAS proteins were shown to interact directly with SOX9 in two-hybrid, co-immunoprecipitation, and electrophoretic mobility shift assays. SOX9 was sumoylated in cotransfection experiments with COS-7 cells using PIAS and SUMO-1 (small ubiquitin-like modifier-1) expression vectors. SOX9 was also sumoylated in vitro by PIAS proteins in the presence of SUMO-1, the SUMOactivating enzyme, and the SUMO-conjugating enzyme. In COS-7 cells, PIAS proteins stimulated the SOX9-dependent transcriptional activity of a Col2a1 promoter-enhancer reporter. This increase in reporter activity was paralleled by an increase in the cellular levels of SOX9. Cotransfection with a SUMO-expressing vector further enhanced the transcriptional activity of this SOX9-dependent Col2a1 reporter in COS-7 cells, and this additional activation was inhibited in the presence of either SUMO-1 mutants or PIAS RING domain mutants or by coexpression of a desumoylation enzyme. Immunofluorescence microscopy of SOX9-transfected COS-7 cells showed that the subnuclear distribution of SOX9 became more diffuse in the presence of PIAS1 and SUMO-1. Our results suggest that, by controlling the cellular concentrations of SOX9, PIAS proteins and sumoylation may be part of a major regulatory system of SOX9 functions.SOX9, a transcription factor of the SRY (sex-determining region, Y chromosome) family, is required for the establishment and differentiation of several cell lineages, including those of chondrocytes, Sertoli cells of male gonads, glial cells of the nervous system, and others. During chondrocyte differentiation, SOX9 is expressed abundantly in mouse chondroprogenitor cells and overtly differentiated chondrocytes (1) and regulates transcription of cartilage-specific extracellular matrix molecules such as collagen types II (2), IX (3), and XI (4) and aggrecan (5). Heterozygous mutations in the Sox9 gene cause campomelic dysplasia, a severe skeletal malformation syndrome characterized by a generalized hypoplasia of endochondral bones. SOX9 inactivation studies in mice indicate that SOX9 has an essential role in several steps of chondrogenic differentiation, including mesenchymal condensations and overt differentiation of chondrocytes (1, 6). In the absence of SOX9, no chondrocyte marker genes are expressed (1), but the precise mechanism of transcriptional activation by SOX9 of cartilage-specific genes is only poorly understood. The cellular concentration of SOX9 must be tightly regulated in vivo given that campomelic dysplasia is due to haploinsufficiency of SOX9 and because a modest increase in SOX9 expression results in dwarfism in mice (7).Members of the SOX9 family of transcription factors contain a high mobility group (HMG) 3 box DNA-binding domain that is at least 50% identical to an equivalent domain in the sex-determining factor SRY...