Modulation of bcl-2 and p27 in human primitive proliferating hematopoietic progenitors by autocrine TGF-β1 is a cell cycle–independent effect and influences their hematopoietic potential

Cells with characteristics of cancer stem/progenitor cells express the CD133 antigen in human endometrial tumors

PURPOSE

Cancer stem cells represent an attractive therapeutic target for tumor eradication. The present study aimed to determine whether CD133 expression may identify cells with characteristics of cancer stem/progenitor cells in human endometrial tumors.

EXPERIMENTAL DESIGN

We analyzed 113 tumor samples for CD133/1 expression by flow cytometry, immunohistochemistry, and semiquantitative reverse transcription-PCR. CD133(+) cells were isolated and used to assess phenotypic characteristics, self-renewal capacity, ability to maintain CD133 expression and form sphere-like structures in long-term cultures, sensitivity to chemotherapeutic agents, gene expression profile, and ability to initiate tumors in NOD/SCID mice.

RESULTS

Primary tumor samples exhibited a variable degree of immunoreactivity for CD133/1, ranging from 1.3% to 62.6%, but stained negatively for other endothelial and stem cell-associated markers. Isolated CD133(+) cells expanded up to 4.6-fold in serum-replenished cultures and coexpressed the GalNAcalpha1-O-Ser/Thr MUC-1 glycoform, a well-characterized tumor-associated antigen. Dissociated bulk tumors formed sphere-like structures; cells grown as tumor spheres maintained CD133 expression and could be propagated for up to 12 weeks. CD133(+) cells purified from endometrioid adenocarcinomas were resistant to cisplatin-induced and paclitaxel-induced cytotoxicity and expressed a peculiar gene signature consisting of high levels of matrix metalloproteases, interleukin-8, CD44, and CXCR4. When serially transplanted into NOD/SCID mice, CD133(+) cells were capable of initiating tumor formation and recapitulating the phenotype of the original tumor.

CONCLUSIONS

CD133 is expressed by human endometrial cancers and might represent a valuable tool to identify cells with cancer stem cell characteristics.

Autocrine transforming growth factor-beta regulation of hematopoiesis: many outcomes that depend on the context

Transforming growth factor-beta (TGF-beta) is a pleiotropic regulator of all stages of hematopoieis. The three mammalian isoforms (TGF-beta1, 2 and 3) have distinct but overlapping effects on hematopoiesis. Depending on the differentiation stage of the target cell, the local environment and the concentration and isoform of TGF-beta, in vivo or in vitro, TGF-beta can be pro- or antiproliferative, pro- or antiapoptotic, pro- or antidifferentiative and can inhibit or increase terminally differentiated cell function. TGF-beta is a major regulator of stem cell quiescence, at least in vitro. TGF-beta can act directly or indirectly through effects on the bone marrow microenvironment. In addition, paracrine and autocrine actions of TGF-beta have overlapping but distinct regulatory effects on hematopoietic stem/progenitor cells. Since TGF-beta can act in numerous steps in the hematopoietic cascade, loss of function mutations in hematopoeitic stem cells (HSC) have different effects on hematopoiesis than transient blockade of autocrine TGF-beta1. Transient neutralization of autocrine TGF-beta in HSC has therapeutic potential. In myeloid and erythroid leukemic cells, autocrine TGF-beta1 and/or its Smad signals controls the ability of these cells to respond to various differentiation inducers, suggesting that this pathway plays a role in determining the cell fate of leukemic cells.

Hematopoietic cytokines, transcription factors and lineage commitment

The past two decades have witnessed significant advances in our understanding of the cellular physiology and molecular regulation of hematopoiesis. At the heart of stem cell self-renewal and lineage commitment decisions lies the relative expression levels of lineage-specific transcription factors. The expression of these transcription factors in early stem cells may be promiscuous and fluctuate, but ultimately comes under the influence of extracellular regulatory signals in the form of hematopoietic cytokines. In this review, we first summarize our current understanding of the phenotypic characterization of hematopoietic stem cells. Next, we describe key known transcription factors which govern stem cell self-renewal and lineage commitment decisions. Finally, we review data concerning the role of specific cytokines in influencing these decisions. From this review, a picture emerges in which stem cell fate decisions are governed by the integrated effects of intrinsic transcription factors and external signaling pathways initiated by regulatory cytokines.

Transcription factor fusions in acute leukemia: variations on a theme

The leukemia-associated fusion proteins share several structural or functional similarities, suggesting that they may impart a leukemic phenotype through common modes of transcriptional dysregulation. The fusion proteins generated by these translocations usually contain a DNA-binding domain, domains responsible for homo- or hetero-dimerization, and domains that interact with proteins involved in chromatin remodeling (e.g., co-repressor molecules or co-activator molecules). It is these shared features that constitute the 'variations on the theme' that underling the aberrant growth and differentiation that is the hallmark of acute leukemia cells.

FLRG, an activin-binding protein, is a new target of TGFbeta transcription activation through Smad proteins

The FLRG gene encodes a secreted glycoprotein that binds to activin and is highly homologous to follistatin, an activin ligand. We cloned the promoter region of the human FLRG gene, and defined the minimal region necessary for transcription activation in a reporter-system assay. We showed that the fragment between positions -130 and +6, which consists of multiple consensus Sp1-binding sites, is required for the constitutive expression of the FLRG gene. We demonstrate here that FLRG mRNA expression is rapidly induced by TGFbeta or by transfection with Smad protein expression vectors in human HepG2 cells. We investigated the transcription-regulation mechanism of FLRG expression in HepG2 cells following treatment with TGFbeta. By deletion and point-mutation analysis of the FLRG promoter, we identified a Smad-binding element involved in the TGFbeta-inducible expression of the FLRG gene. Moreover, transactivation of the FLRG promoter by TGFbeta was compromised by dominant-negative mutants of Smad3 and Smad4 proteins. In addition, gel electrophoresis mobility-shift assays demonstrated the specific interaction of Smad3 and Smad4 proteins with the Smad-binding element consensus motif found in the FLRG promoter. Taken together, our data imply that Smad proteins participate in the regulation of expression of FLRG, a new target of TGFbeta transcription activation.

Transforming growth factor-β: pleiotropic role in the regulation of hematopoiesis

Hematopoiesis is a remarkable cell-renewal process that leads to the continuous generation of large numbers of multiple mature cell types, starting from a relatively small stem cell compartment. A highly complex but efficient regulatory network is necessary to tightly control this production and to maintain the hematopoietic tissue in homeostasis. During the last 3 decades, constantly growing numbers of molecules involved in this regulation have been identified. They include soluble cytokines and growth factors, cell–cell interaction molecules, and extracellular matrix components, which provide a multifunctional scaffolding specific for each tissue. The cloning of numerous growth factors and their mass production have led to their possible use for both fundamental research and clinical application.