Elsevier

Leukemia Research

Volume 30, Issue 2, February 2006, Pages 183-189
Leukemia Research

Transferrin receptor-1 and 2 expression in chronic lymphocytic leukemia

https://doi.org/10.1016/j.leukres.2005.06.006Get rights and content

Abstract

Transferrin receptor (TfR)-1 and 2 mRNA and CD71 (TfR1) expression was analyzed in 118 CLL patients. Ninety-five out of 109 analyzed cases expressed CD71, mostly at a high level; 60% of CD71 (+) cases were IGH-mutated. All samples were TfR1 mRNA (+); TfR2-alpha/beta mRNA was detected in, respectively, 52/102 and 100/109 cases. Competitive RT-PCR showed widely divergent levels of TfR1 mRNA in cases with high CD71 expression, alluding to postrtanscriptional control of TfR1 expression in CLL. The almost uniformly high CD71 expression in CLL is in keeping with the activated status of neoplastic cells, regardless of IGH mutational load.

Introduction

The best known mechanism for the uptake of iron in both normal and neoplastic cells entails binding of serum transferrin (the main carrier protein for iron in serum) to a specific transmembrane glycoprotein receptor (transferrin receptor, TfR1; CD71) [1], [2]. In most tissues, TfR1 expression is controlled at the post-transcriptional level in a manner resembling feedback inhibition [3], [4]: fewer receptors are expressed when iron is abundant and more receptors are expressed when iron is scarce. However, there is no doubt that transcriptional mechanisms are involved in TfR1 expression as well, and they may play a more significant role in tissue- and stage-specific regulation [4]. Transcriptional regulation is also involved both in TfR1 induction during erythroid differentiation and T/B cell activation and in TfR1 down-regulation during terminal differentiation of myeloid and lymphoid leukaemic cell lines [1], [2].

Except for mature erythrocytes and some other terminally differentiated cells, TfR1 is probably expressed on all cells but expression levels vary greatly. TfR1 (CD71) expression is related to the proliferative state of the cells as well as the induction of differentiation [5]; thus, the number of TfR1 (CD71) molecules is larger in cells with a high proliferation rate. Furthermore, CD71 is one of the “classical” activation markers up-regulated upon B cell activation [2], [3].

In 1999, Kawabata et al. cloned a second human transferrin receptor-2 (TfR2) that has significant sequence homology with TfR1 in the extracellular domain; TfR2 also binds transferrin (albeit with lower affinity than TfR1) but is apparently not regulated by intracellular iron concentration [6], [7]. Two alternatively spliced transcripts (alpha and beta) are transcribed from the TfR2 gene [6], [7]. Initially, based on the finding of high TfR2 mRNA expression in erythroid precursor cells and AML FAB-M6 cases (4/7 cases) as well as in samples from patients with myelodysplastic syndromes with erythroid hyperplasia it was proposed that TfR2 might be considered as a marker of erythroid cells [7]. Nevertheless, as we have subsequently shown, not only erythroid but also myeloid and lymphoid cells can strongly express TfR2 mRNA, suggesting that TfR2 mRNA expression is not restricted to erythroid cells [8].

B cell activation is generally accompanied by changes in the cell surface expression and/or density of certain critical functional molecules. B cell lymphocytic leukemia (B-CLL) cells express (albeit in varying degrees) the classical activation markers CD23, CD25, CD69 and CD71; the increased expression of CD5 and CD27 on B-CLL cells is in line with the activation hypothesis, since both markers can be up-regulated upon cellular activation [9]. CD69 and CD71 are indicators of cellular activation that follow different kinetics of expression [10], [11], [12]. An association between CD71 expression and mutated immunoglobulin (IG) genes was recently reported in a series of 61 patients with CLL; in contrast, CD69 was expressed significantly more often in CLL cases with unmutated genes [9].

In the present study, we assessed TfR1 gene expression at both the protein and the mRNA level (qualitatively and quantitatively) in a series of 118 CLL patients; furthermore, we conducted a parallel analysis of TfR2 gene expression and explored possible associations between TfR1 mRNA levels, CD71 expression, as well as expression of other activation markers and IGHV mutation status.

Section snippets

Patient samples

Peripheral blood samples were collected from 118 patients with typical B-CLL (CD5+, CD19+, CD20+ and CD23+). All patients met the diagnostic criteria of the National Cancer Institute-Working Group [13]. The present series included 65/118 males and 53/118 females with a median age of 67 years (range 29–79). Most patients were at early clinical stages by Rai classification (stage 0: 56 patients; stage I: 31 patients; stage II: 22 patients); only 9 patients were diagnosed with advanced disease

Immunophenotypic results

Flow cytometric analysis of surface markers related to activation/differentiation state of the malignant clone was performed in peripheral blood samples of 118 patients with B-CLL (CD5+, CD19+, CD20+ and CD23+). In all samples, the tumor load was at least 70%. Ninety out of 109 analyzed cases were sIgM+ (52 kappa; 38 lambda) and 19 were sIgG+ (13 kappa; 6 lambda). Ninety-five out of 109 analyzed cases expressed CD71 (87.2%), while the remainder (14/109; 12.8%) were CD71-negative (Table 2). The

Discussion

CD71 has been detected on the cell surface of dividing cells of all hematopoietic cell lines as well as malignant myeloid and lymphoid cells. It is generally expressed more strongly by proliferating cells, albeit with varying levels of expression, which could probably be attributed to different demands for iron [1], [2], [3], [4]. TfR is required not only for normal erythropoiesis, but also for the proliferation and/or maturation of other hematopoietic cell types. Little, if any, TfR is

Conclusions

Molecular and immunophenotypic analysis of transferrin receptor-1 (CD71) and TfR2 expression in CLL demonstrated almost ubiquitous CD71 expression regardless of IGH mutation status. This finding provides further evidence that the surface membrane phenotypes of CLL cells reflect their antigenic and activation experiences. High CD71 expression in the context of widely divergent TfR1 mRNA levels alludes to post-transcriptional control of TfR1 gene expression in CLL; however, the possibility of

Acknowledgements

Dr. Smilevska is recipient of a scholarship from the Foundation of State Scholarships of Greece (IKY). The authors wish to thank Prof. Marie-Paule Lefranc and Dr. Veronique Giudicelli (Laboratoire d’Immunogenetique Moleculaire, LIGM, Universite Montpellier II, UPR CNRS) for valuable help in IG analysis.

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