RTP801 is a novel retinoic acid-responsive gene associated with myeloid differentiation.

Objective: Retinoids are crucial in the regulation of fundamental cellular processes including terminal differentiation of both normal and malignant myeloid progenitors. The aim of this study was to identify and characterize retinoic acid (RA) target genes.

Methods And Results: RTP801 is a recently cloned stress response gene that acts as a negative regulator of the mTOR pathway.

Detection of aberrant gene expression in CD34+ hematopoietic stem cells from patients with agnogenic myeloid metaplasia using oligonucleotide microarrays.

Agnogenic myeloid metaplasia (AMM) is a clonal stem cell disorder that leads to ineffective hematopoiesis, bone marrow fibrosis, and extramedullary hematopoiesis. The molecular mechanisms underlying the development of this syndrome are currently unknown. Therefore, the aim of this study was to characterize aberrant gene expression in CD34+ hematopoietic stem cells from patients with AMM.

Protein partners of C/EBPepsilon.

CCAAT-enhancer binding protein-epsilon (C/EBPepsilon) is a nuclear transcription factor implicated in the regulation of terminal myeloid differentiation. Using a yeast two-hybrid screen, potential interaction partners of C/EBPepsilon involved in myeloid development were identified. C/EBPepsilon was found to associate with other C/EBP family members, including C/EBPepsilon and CHOP as well as other proteins that are known to contain a leucine-zipper protein interaction motif including CREB2, LDOC1, E6TP1, and AF-17.

Retinoic acid regulates C/EBP homologous protein expression (CHOP), which negatively regulates myeloid target genes.

Retinoic acid (RA) promotes granulocytic differentiation of normal hematopoietic cells and acute promyelocytic leukemia (APL) blasts by transcriptional modulation of myeloid regulatory genes. In this study, we have identified the C/EBP homologous protein (CHOP) as a novel retinoid-responsive gene using a polymerase chain reaction (PCR)-based cDNA subtraction method. All-trans retinoic acid (ATRA) induced a biphasic expression of CHOP mRNA in the NB4 and HL60 AML cell lines.

Restoration of C/EBPalpha expression in a BCR-ABL+ cell line induces terminal granulocytic differentiation.

The transcription factor C/EBPalpha plays a critical role in the process of granulocytic differentiation. Recently, mutations that abrogated transcriptional activation of C/EBPalpha were detected in acute myeloid leukemia patient samples. Moreover, the progression of chronic myelogenous leukemia (CML) to blast crisis in patients was correlated with down-modulation of C/EBPalpha.

Comparative analysis of genes regulated by PML/RAR alpha and PLZF/RAR alpha in response to retinoic acid using oligonucleotide arrays.

Acute promyelocytic leukemia (APL) is associated with chromosomal translocations involving retinoic acid receptor alpha (RAR alpha) and its fusion partners including promyelocytic leukemia (PML) and promyelocytic leukemia zinc finger (PLZF). Using oligonucleotide arrays, we examined changes in global gene expression mediated by the ectopic expression of either PML/RAR alpha (retinoid-sensitive) or PLZF/RAR alpha (retinoid-resistant) in U937 cells. Of more than 5000 genes analyzed, 16 genes were commonly up-regulated, and 57 genes were down-regulated by both fusion proteins suggesting their role in the APL phenotype.

Macrophage functional maturation and cytokine production are impaired in C/EBP epsilon-deficient mice.

Members of the CCAAT/enhancer-binding protein (C/EBP) family are involved in the regulation of cellular differentiation and function of many tissues. Unlike the other members of the family, C/EBP epsilon expression is restricted to granulocytes, macrophages, and lymphocytes. C/EBP epsilon is highly conserved between human and rodents and is essential for terminal granulopoiesis in both species.