BOB.1 of the channel catfish, Ictalurus punctatus: not a transcriptional coactivator?

Novel small molecular inhibitor of Pit-Oct-Unc transcription factor 1 suppresses hepatocellular carcinoma cell proliferation

Hepatocellular carcinoma (HCC) is one of the most prevalent fatal malignancies in the Chinese population, due to high rates of hepatitis virus infection. Molecular targeted drugs such as sorafenib are the anti-tumor agents of choice for HCC treatment, but their results are generally unsatisfactory. In the present study the use of Pit-Oct-Unc transcription factor 1 (OCT1/POU2F1) as a potential therapeutic target for HCC was investigated, and a novel small molecular inhibitor of OCT1 (SMIO-1) was designed and its therapeutic efficacy against HCC was assessed. OCT1 expression was higher in HCC specimens than in corresponding non-tumor tissues, and higher OCT1 was associated with poorer prognosis in advanced HCC patients undergoing sorafenib treatment. For the first time, the novel SMIO-1 was investigated in conjunction with OCT1 via molecular docking. Interaction between SMIO-1 and OCT1 was confirmed via OCT1 point mutation. Treatment with SMIO-1 repressed OCT1 transcription factor activation by disrupting the interaction between OCT1 and its cofactors. It also repressed the proliferation and metastasis of HCC cells, and inhibited proliferation-related and metastasis-related genes downstream of OCT1. Therefore, SMIO-1 is a promising strategy for HCC treatment.

A C-terminal acidic domain regulates degradation of the transcriptional coactivator Bob1

Bob1 (Obf-1 or OCA-B) is a 34-kDa transcriptional coactivator encoded by the Pou2af1 gene that is essential for normal B-cell development and immune responses in mice. During lymphocyte activation, Bob1 protein levels dramatically increase independently of mRNA levels, suggesting that the stability of Bob1 is regulated. We used a fluorescent protein-based reporter system to analyze protein stability in response to genetic and physiological perturbations and show that, while Bob1 degradation is proteasome mediated, it does not require ubiquitination of Bob1. Furthermore, degradation of Bob1 in B cells appears to be largely independent of the E3 ubiquitin ligase Siah. We propose a novel mechanism of Bob1 turnover in B cells, whereby an acidic region in the C terminus of Bob1 regulates the activity of degron signals elsewhere in the protein. Changes that make the C terminus more acidic, including tyrosine phosphorylation-mimetic mutations, stabilize the instable murine Bob1 protein, indicating that B cells may regulate Bob1 stability and activity via signaling pathways. Finally, we show that expressing a stable Bob1 mutant in B cells suppresses cell proliferation and induces changes in surface marker expression commonly seen during B-cell differentiation.

Immunoglobulin genes and their transcriptional control in teleosts

Immunoglobulin (Ig), which exists only in jawed vertebrates, is one of the most important molecules in adaptive immunity. In the last two decades, many teleost Ig genes have been identified by in silico data mining from the enormous gene and EST databases of many fish species. In this review, the organization of Ig gene segments, the expressed Ig isotypes and their transcriptional controls are discussed. The Ig heavy chain (IgH) locus in teleosts encodes the variable (V), the diversity (D), the joining (J) segments and three different isotypic constant (C) regions including Cμ, Cδ, and Cζ/τ genes, and is organized as a "translocon" type like the IgH loci of higher vertebrates. In contrast, the Ig light (L) chain locus is arranged in a "multicluster" or repeating set of VL, JL, and CL segments. The IgL chains have four isotypes; two κ L1/G and L3/F), σ (L2) and λ. The transcription of IgH genes in teleosts is regulated by a VH promoter and the Eμ3' enhancer, which both function in a B cell-specific manner. The location of the IgH locus, structure and transcriptional function of the Eμ3' enhancer are important to our understanding of the evolutional changes that have occurred in the IgH gene locus.

Enhancer-promoter communication and transcriptional regulation of Igh

Transcriptional regulation of eukaryotic protein-coding genes requires the participation of site-specific transcription factors that bind distal regulatory elements, as well as factors that, together with RNA polymerase II, form the basal transcription machinery at the core promoter. Gene regulation requires proper communication between promoters and enhancers, often over great distances. Therefore, it is important to understand the potentially inter-related transcription factor interactions at both of these elements. How this is achieved on tissue-specific genes, such as the immunoglobulin heavy chain (IgH) in B cells remains unclear. Here, we review known interactions at the Igh variable region (V(H)) promoters and present our perspective on promoter-enhancer interactions that are likely important for Ig gene regulation in B cells.