HEXIM1 Induces Differentiation of Human Pluripotent Stem Cells

Abstract

Hexamethylene bisacetamide inducible protein 1 (HEXIM1) is best known as the inhibitor of positive transcription elongation factor b (P-TEFb), which is composed of cyclin-dependent kinase 9 (CDK9)/cyclin T1. P-TEFb is an essential regulator for the transcriptional elongation by RNA polymerase II. A genome-wide study using human embryonic stem cells shows that most mRNA synthesis is regulated at the stage of transcription elongation, suggesting a possible role for P-TEFb/HEXIM1 in the gene regulation of stem cells. In this report, we detected a marked increase in HEXIM1 protein levels in the differentiated human pluripotent stem cells (hPSCs) induced by LY294002 treatment. Since no changes in CDK9 and cyclin T1 were observed in the LY294002-treated cells, increased levels of HEXIM1 might lead to inhibition of P-TEFb activity. However, treatment with a potent P-TEFb inhibiting compound, flavopiridol, failed to induce hPSC differentiation, ruling out the possible requirement for P-TEFb kinase activity in hPSC differentiation. Conversely, differentiation was observed when hPSCs were incubated with hexamethylene bisacetamide, a HEXIM1 inducing reagent. The involvement of HEXIM1 in the regulation of hPSCs was further supported when overexpression of HEXIM1 concomitantly induced hPSC differentiation. Collectively, our study demonstrates a novel role of HEXIM1 in regulating hPSC fate through a P-TEFb-independent pathway.

ESCDL-1, a new cell line derived from chicken embryonic stem cells, supports efficient replication of Mardiviruses

“…From cES cells exposed to the differentiating stimuli described in our protocol, we derived the ESCDL-1 that were further characterized after initially testing permissive for GaHV-2 replication. The expression of mesenchyme lineage markers by ESCDL-1, in particular with no detectable expression of cytokeratins, high expression of VIM, THY1, NGF, ENDOG and PDGFRB genes and high expression of the FOXC2 specific transcription factor, is in good agreement with the known effect of HMBA as a strong inducer of markers of the mesodermal lineage in human ES cells [ 60 ]. We also report on the differential expression of numerous integrins including ITGB5, which was shown to play a major role in Epithelial-Mesenchymal-Transition (EMT) [ 61 ] and of specific forkhead transcription factors, members of the CEBP and FOX families, all indicating a strong connexion with the mesenchymal phenotype for ESCDL-1.…”

eIF4A2 targets developmental potency and histone H3.3 transcripts for translational control of stem cell pluripotency

“…3A , bottom, and table S4). Among the 60 up-regulated genes, many genes can induce ESC differentiation or are important for cellular development, such as hexamethylene bis-acetamide inducible 1 (Hexim1) ( 25 ), transcription factor 12 (Tcf12) ( 26 ), transcription factor 3 (Tcf3) ( 27 ), and tet methylcytosine dioxygenase 1 (Tet1) ( 28 ). Thus, in eIF4A2-depleted ESCs, the overexpression of these genes (at protein level) may contribute to the loss of pluripotency and cellular differentiation.…”

“…Apart from roles in translation activation, eIF4A2 is also responsible for translation repression of many differentiation-promoting genes such as Hexim1 ( 25 ), Tcf12 ( 26 ), Tcf3 ( 27 ), and Tet1 ( 28 ) ( Fig. 3A , bottom).…”

eIF4A2 targets developmental potency and histone H3.3 transcripts for translational control of stem cell pluripotency

“…3A bottom and table S4). Among the 60 upregulated genes, many genes can induce ESC differentiation or are important for cellular development, such as Hexim1 ( 25 ), Tcf12 ( 26 ), Tcf3 ( 27 ), and Tet1 ( 28 ). Thus, in eIF4A2-depleted ESCs, the overexpression of these genes (at protein level) may contribute to the loss of pluripotency and cellular differentiation.…”