Brf1 loss and not overexpression disrupts tissues homeostasis in the intestine, liver and pancreas

RNA polymerase III (Pol-III) transcribes tRNAs and other small RNAs essential for protein synthesis and cell growth. Pol-III is deregulated during carcinogenesis; however, its role in vivo has not been studied. To address this issue, we manipulated levels of Brf1, a Pol-III transcription factor that is essential for recruitment of Pol-III holoenzyme at tRNA genes in vivo. Knockout of Brf1 led to embryonic lethality at blastocyst stage. In contrast, heterozygous Brf1 mice were viable, fertile and of a normal size. Conditional deletion of Brf1 in gastrointestinal epithelial tissues, intestine, liver and pancreas, was incompatible with organ homeostasis. Deletion of Brf1 in adult intestine and liver induced apoptosis. However, Brf1 heterozygosity neither had gross effects in these epithelia nor did it modify tumorigenesis in the intestine or pancreas. Overexpression of BRF1 rescued the phenotypes of Brf1 deletion in intestine and liver but was unable to initiate tumorigenesis. Thus, Brf1 and Pol-III activity are absolutely essential for normal homeostasis during development and in adult epithelia. However, Brf1 overexpression or heterozygosity are unable to modify tumorigenesis, suggesting a permissive, but not driving role for Brf1 in the development of epithelial cancers of the pancreas and gut.

Alcohol Intake and Abnormal Expression of Brf1 in Breast Cancer

Breast cancer is the most common malignant disease of females. Overall, one woman in every nine will get breast cancer at some time in her life. Epidemiological studies have indicated that alcohol consumption has most consistently been associated with breast cancer risk. However, the mechanism of alcohol-associated breast cancer remains to be addressed. Little is known about the effects of alcohol consumption on Brf1 (TFIIIB-related factor 1) expression and RNA Pol III gene (RNA polymerase III-dependent gene) transcription, which are responsible for protein synthesis and tightly linked to cell proliferation, cell transformation, and tumor development. Emerging evidences have indicated that alcohol induces deregulation of Brf1 and Pol III genes to cause the alterations of cell phenotypes and tumor formation. In this paper, we summarize the progresses regarding alcohol-caused increase in the expression of Brf1 and Pol III genes and analysis of its molecular mechanism of breast cancer. As the earlier and accurate diagnosis approach of breast cancer is not available yet, exploring the molecular mechanism and identifying the biomarker of alcohol-associated breast cancer are especially important. Recent studies have demonstrated that Brf1 is overexpressed in most ER+ (estrogen receptor positive) cases of breast cancer and the change in cellular levels of Brf1 reflects the therapeutic efficacy and prognosis of this disease. It suggests that Brf1 may be a potential diagnosis biomarker and a therapeutic target of alcohol-associated breast cancer.

The significance of Brf1 overexpression in human hepatocellular carcinoma

Brf1 (TFIIB-related factor 1) plays a crucial role in cell transformation and tumorigenesis. However, the significance of Brf1 expression in human HCC (hepatocellular carcinoma) cases remains to be addressed. In this study, biopsies of human HCC, liver tumor samples of mice and cell lines of normal and tumor liver were utilized to determine the alteration of Brf1 expression using cytological and molecular biological approaches. Brf1 expression is increased in human HCC cases, which is correlated with shorter survival times. Levels of Brf1 and Pol III (RNA polymerase III-dependent) gene transcription in HCC patients with alcohol consumption are higher than the cases of non-HCC with or without alcohol intake. Induction of Brf1 and Pol III genes by ethanol in hepatoma cells is higher than in non-tumor cells. Ethanol increases the rate of cell transformation. Repression of Brf1 inhibits alcohol-promoted cell transformation. Alcohol consumption enhances Brf1 expression to promote cell transformation. These studies demonstrate that Brf1 is a new biomarker of HCC.

Tamoxifen represses alcohol-induced transcription of RNA polymerase III-dependent genes in breast cancer cells

Alcohol consumption in women has been associated with an increased risk of breast cancer, particular in estrogen receptor positive (ER+) cases. Deregulation of RNA polymerase III-dependent (Pol III) transcription enhances cellular tRNAs and 5S rRNA production, leading to an increase in translational capacity to promote cell transformation and tumor formation. Our recent studies demonstrated that alcohol induces Brf1 expression and Pol III gene transcription via ER. Here, we report that Tamoxifen (Tam) inhibits the induction of Brf1 and Pol III genes in ER+ breast cancer cells. Further analysis indicates that alcohol increases c-Jun expression to upregulate the transcription of Brf1 and Pol III genes, whereas Tam reduces c-Jun expression to repress the transcription of Brf1. Repression of cJun decreases cellular levels of ERα and Brf1. Alcohol-dependent increased occupancy of Brf1 in Pol III gene promoters is reduced by Tam. The repression of Brf1 and Pol III genes by Tam reduces alcohol-induced cell proliferation and colony formation. Together, these results indicate that Tam inhibits alcohol-induced Brf1 expression through c-Jun and ERα to downregulate Pol III gene transcription. Our studies uncover a new mechanism of Tam-treated ER+ breast cancer, by which Tam inhibits tumor growth through repressing Pol III gene transcription.

[Proteomic expression analysis of human colorectal cancer: of soluble overexpressed proteins]

Colon cancer is one of the leading causes of cancer deaths in developed countries due to the absence of tumor specific markers for early diagnosis of the disease, providing adequate sensitivity. Search for diagnostic markers of various types of cancer by proteomic approaches has been limited by large differences in protein centration. We used preliminary extraction of major cellular proteins by 0.2 M sodium chloride in presence of nonionic detergent NP-40 in order to raise the sensitivity of the 2D PAGE detection of low-abundant soluble proteins, some of which may penetrate in blood circulation during carcinogenesis. Application of this procedure prior to 2D comparative analysis of proteomes of normal tissues and matched colon cancer specimens led to selection of ten proteins, which are frequently overexpressed in colon adenocarcinomas. Mass-spectrometric identification of selected proteins led to discovery of two novel protein markers of colon tumors--TAF9 and CISH. Low level of CISH expression in various tissues suggests that it is a novel prospective marker for diagnosis of colon cancer.

Production and isotope labeling of antimicrobial peptides in Escherichia coli by means of a novel fusion partner that enables high-yield insoluble expression and fast purification

A method is presented that allows efficient production of antimicrobial peptides in bacteria by means of fusion to the histone fold domain of the human transcription factor TAF12. This small fusion partner drives high-level expression of peptides and leads to their accumulation in an entirely insoluble form, thereby eliminating toxicity to the host. Using the antimicrobial peptide LAH4 as an example, we demonstrate that neither affinity purification of the TAF12 fusion protein nor initial solubilization of inclusion bodies in denaturing buffers is required. Instead, crude insoluble material from bacteria is directly dissolved in formic acid for immediate release of the peptide through chemical cleavage at a unique Asp-Pro site. This is followed by purification to homogeneity in a single chromatographic step. Because of the elevated expression levels of the histone fold domain and its small size (8 kDa), this straightforward purification scheme produces yields in excess of 10 mg active peptide per liter of culture. We demonstrate that TAF12 fusion allows expression of a wide range of antimicrobial peptides as well as efficient isotope labeling for NMR studies.

G1 arrest induction represents a critical determinant for cisplatin cytotoxicity in G1 checkpoint-retaining human cancers

Cisplatin has been used effectively to treat various human cancer types; yet, the precise mechanism underlying its cytotoxicity remains unknown. In eukaryotes, progression through G1 is monitored by a checkpoint, which executes G1 arrest in the event of DNA damage to allow time for repair before initiating DNA replication. The retinoblastoma tumor suppressor gene is an integral component of the mammalian G1 checkpoint. The utility of the retinoblastoma gene as a therapeutic for human cancers has been investigated. Intriguingly, the cytotoxicity profile of the retinoblastoma gene therapy closely parallels the clinical targets of cisplatin. It prompted an investigation into the potential role of the checkpoint-induced G1 arrest in cisplatin cytotoxicity. Here, the evidence that G1 arrest induction represents a critical step in cisplatin-induced lytic path is presented. First, cisplatin-treated human cancer cells undergo a prolonged G1 arrest before dying. Second, triggering G1 arrest via infection with a recombinant adenovirus expressing the human retinoblastoma gene is sufficient to potentiate lethality in the absence of cisplatin. Third, the extent of the lethality induced correlates with the G1-arresting potential of the ectopically expressed human retinoblastoma polypeptide. Fourth, human cancer cells resistant to cisplatin do not undergo G1 arrest despite cisplatin treatment. The above mechanism may be exploited to develop therapeutics that preserve the efficacy of cisplatin yet bypass its mutagenicity associated with the formation of secondary tumors.

Regulated expression of TAF1 in 1-cell mouse embryos

TATA binding protein (TBP) associated factor 1 (TAF1) is a member of the general transcription machinery. Interference in the function of TAF1 causes a broad transcriptional defect in early development. To explore possible roles of TAF1 in embryonic transcriptional silence and zygotic genome activation, we examined the expression of TAF1 in 1-cell mouse embryos. Using an immunofluorescence assay, TAF1 was not detected in embryos in the first few hours after fertilization. TAF1 appeared in pronuclei 6 h post-fertilization and reached a relatively high level before zygotic genome activation. These data show that besides TBP, another critical member of the general transcription machinery such as TAF1 is also absent or at an extremely low level at the outset of development. Combined deficiency in critical members of the general transcription machinery may account for embryonic transcriptional silence.

A functional interaction between ATF7 and TAF12 that is modulated by TAF4

The ATF7 proteins, which are members of the cyclic AMP responsive binding protein (CREB)/activating transcription factor (ATF) family of transcription factors, display quite versatile properties: they can interact with the adenovirus E1a oncoprotein, mediating part of its transcriptional activity; they heterodimerize with the Jun, Fos or related transcription factors, likely modulating their DNA-binding specificity; they also recruit to the promoter a stress-induced protein kinase (JNK2). In the present study, we investigate the functional relationships of ATF7 with hsTAF12 (formerly hsTAF(II)20/15), which has originally been identified as a component of the general transcription factor TFIID. We show that overexpression of hsTAF12 potentiates ATF7-induced transcriptional activation through direct interaction with ATF7, suggesting that TAF12 is a functional partner of ATF7. In support of this conclusion, chromatin immunoprecipitation experiments confirm the interaction of ATF7 with TAF12 on an ATF7-responsive promoter, in the absence of any artificial overexpression of both proteins. We also show that the TAF12-dependent transcriptional activation is competitively inhibited by TAF4. Although both TAF12 isoforms (TAF12-1 and -2, formerly TAF(II)20 and TAF(II)15) interact with the ATF7 activation region through their histone-fold domain, only the largest, hsTAF12-1, mediates transcriptional activation through its N-terminal region.

In vivo synthesis of Taf1p lacking the TAF N-terminal domain using alternative transcription or translation initiation sites

The TAF N-terminal domain (TAND) of TAF1 includes two subdomains, TAND1 and TAND2, which bind to the concave and convex surfaces of TBP, respectively. Previous studies showed that the substitution of yeast TAND1 or TAND2 with the equivalent domain from a Drosophila homologue leads to accumulation of truncated Taf1p in yeast. This study demonstrates that these truncated Taf1p derivatives lack TAND. However, full-length Taf1p and untruncated derivatives are produced in yeast when several Met-to-Ala mutations are introduced in the carboxy-terminus of TAND. In contrast, mutations that reduce expression of full-length TAF1 do not reduce the amount of truncated Taf1p derivatives that are produced. These data suggest that TAND-deficient TAF1 derivatives are produced by initiating translation at alternative initiation sites. In addition, the TAF1 mRNA structure suggests that the TAND-deficient TAF1 derivatives may also be formed in yeast by use of (cryptic) alternative transcription initiation sites. Importantly, TAND-deficient truncated Taf1p appears to be produced at a low level in wild-type yeast as well. Finally, this study also demonstrates that Drosophila TAND2 substitutes functionally for yeast TAND2, but Drosophila TAND1 does not substitute for yeast TAND1.