Microarray Analysis of LIF/Stat3 Transcriptional Targets in Embryonic Stem Cells

Involvement of HTLV-I Tax and CREB in aneuploidy: a bioinformatics approach

Background

Adult T-cell leukemia (ATL) is a complex and multifaceted disease associated with human T-cell leukemia virus type 1 (HTLV-I) infection. Tax, the viral oncoprotein, is considered a major contributor to cell cycle deregulation in HTLV-I transformed cells by either directly disrupting cellular factors (protein-protein interactions) or altering their transcription profile. Tax transactivates these cellular promoters by interacting with transcription factors such as CREB/ATF, NF-κB, and SRF. Therefore by examining which factors upregulate a particular set of promoters we may begin to understand how Tax orchestrates leukemia development.

Results

We observed that CTLL cells stably expressing wild-type Tax (CTLL/WT) exhibited aneuploidy as compared to a Tax clone deficient for CREB transactivation (CTLL/703). To better understand the contribution of Tax transactivation through the CREB/ATF pathway to the aneuploid phenotype, we performed microarray analysis comparing CTLL/WT to CTLL/703 cells. Promoter analysis of altered genes revealed that a subset of these genes contain CREB/ATF consensus sequences. While these genes had diverse functions, smaller subsets of genes were found to be involved in G2/M phase regulation, in particular kinetochore assembly. Furthermore, we confirmed the presence of CREB, Tax and RNA Polymerase II at the p97Vcp and Sgt1 promoters in vivo through chromatin immunoprecipitation in CTLL/WT cells.

Conclusion

These results indicate that the development of aneuploidy in Tax-expressing cells may occur in response to an alteration in the transcription profile, in addition to direct protein interactions.

Lefty at the crossroads of "stemness" and differentiative events

Stem cells are functionally defined by their ability to self-renew and generate a progeny capable of creation or reconstitution of various tissues. Microarray analysis has shown a member of the transforming growth factor (TGF)-beta superfamily, Lefty, to be the single most abundant inhibitor in stem cells and in maternal decidua that supports embryo implantation. Lefty is regulated by pathways such as Smad (Sma and Mad [mothers against decapentaplegic]) and WNT (wingless-type) and by the transcriptional factor Oct3/4 (octamer-binding transcription factor 3/4), which support "stemness." Lefty is also induced upon exit from the state of stemness, including forced in vitro differentiation, and leukemia inhibitory factor withdrawal. Lefty is a candidate in cell-fate decisions because of its unique ability to modulate the expression of TGF-beta family proteins such as Nodal and by blanket inhibition of the activity of members of this family which require EGF-CFC (epidermal growth factor-Cripto, Frl-1, and Cryptic) as a coreceptor.