dELL, a drosophila homologue of transcription elongation factor ELL (Eleven-nineteen Lysine rich Leukemia), is required for early development

SEC: A core hub during cell fate alteration

Pol II pause release is a rate-limiting step in gene transcription, influencing various cell fate alterations. Numerous proteins orchestrate Pol II pause release, thereby playing pivotal roles in the intricate process of cellular fate modulation. Super elongation complex (SEC), a large assembly comprising diverse protein components, has garnered attention due to its emerging significance in orchestrating physiological and pathological cellular identity changes by regulating the transcription of crucial genes. Consequently, SEC emerges as a noteworthy functional complex capable of modulating cell fate alterations. Therefore, a comprehensive review is warranted to systematically summarize the core roles of SEC in different types of cell fate alterations. This review focuses on elucidating the current understanding of the structural and functional basis of SEC. Additionally, we discuss the intricate regulatory mechanisms governing SEC in various models of cell fate alteration, encompassing both physiological and pathological contexts. Furthermore, leveraging the existing knowledge of SEC, we propose some insightful directions for future research, aiming to enhance our mechanistic and functional comprehension of SEC within the diverse landscape of cell fate alterations.

Apoptosis induction and growth suppression by U19/Eaf2 is mediated through its ELL-binding domain

BACKGROUND

U19/Eaf2 is an androgen-response gene and its downregulation is frequently observed in advanced human prostate cancer. U19/Eaf2 interacts with ELL, a fusion partner of MLL in the (11;19) (q23;p13.1) translocation in acute myeloid leukemia. U19/Eaf2 overexpression induces apoptosis and suppresses xenograft tumor growth.

METHODS

Transfection and colony formation were used to assay for apoptosis and growth suppression of various U19/Eaf2 mutants. Co-immunoprecipitation was performed to test the interaction between the U19/Eaf2 constructs and ELL.

RESULTS

The region of U19/Eaf2 essential for apoptosis and growth suppression was mapped to amino acids 68-113. This region was necessary and sufficient for binding ELL. Co-expression of U19/Eaf2 and ELL in 293 cells lead to significant increase in cell death and growth suppression.

CONCLUSIONS

These observations argue that the interaction with ELL is essential for the induction of apoptosis and growth suppression by U19/Eaf2.

Inhibition of the canonical Wnt signaling pathway in cytoplasm: a novel property of the carboxyl terminal domains of two Xenopus ELL genes

The Wnt signaling pathways are important in many developmental events. The canonical Wnt pathway is one of the three major Wnt-mediated intracellular signaling pathways and is thought to activate Dvl followed by the stabilization of beta-catenin. In Xenopus, this pathway is involved in dorsal determination, anterior-posterior patterning during gastrulation, and neural induction. Here we describe a role for the Xenopus ELL (Eleven-nineteen Lysine-rich Leukemia) gene product in canonical Wnt signaling. Translocation of ELL has been associated with acute myeloid leukemia and the protein possesses three functional domains. We identified rELL-C from a rat brain cDNA library as a binding factor for Dishevelled (Dvl); it represents a partial sequence of rat ELL lacking the pol II elongation domain and has been shown to suppress canonical Wnt signaling. Next, we isolated two Xenopus homologs of ELL, xELL1 and xELL2. No obvious phenotypes were observed with microinjection of full-length xELL1 or xELL2 mRNA, however, microinjection with their occludin homology domain inhibited Wnt signaling at the level of Dvl and upstream of beta-catenin. Intracellular localization of microinjected xELL1- and xELL2-GFP mRNAs showed localization of the full-length products in the nucleus and the occludin-homology domain products in cytoplasm. These results raise the possibility that ELL, which is thought to function as a transcription factor in nuclei, can serve other, novel roles to suppress canonical Wnt signaling in the cytoplasm.

The RNA polymerase II elongation complex

Synthesis of eukaryotic mRNA by RNA polymerase II is an elaborate biochemical process that requires the concerted action of a large set of transcription factors. RNA polymerase II transcription proceeds through multiple stages designated preinitiation, initiation, and elongation. Historically, studies of the elongation stage of eukaryotic mRNA synthesis have lagged behind studies of the preinitiation and initiation stages; however, in recent years, efforts to elucidate the mechanisms governing elongation have led to the discovery of a diverse collection of transcription factors that directly regulate the activity of elongating RNA polymerase II. Moreover, these studies have revealed unanticipated roles for the RNA polymerase II elongation complex in such processes as DNA repair and recombination and the proper processing and nucleocytoplasmic transport of mRNA. Below we describe these recent advances, which highlight the important role of the RNA polymerase II elongation complex in regulation of eukaryotic gene expression.