Deregulated expression of promyelocytic leukemia zinc finger protein in B-cell chronic lymphocytic leukemias does not affect cyclin A expression.
BACKGROUND
The promyelocytic leukemia zinc finger (PLZF) gene encodes a transcription factor expressed in myeloid, lymphoid and CD34(+) progenitor cells. Structurally related to BCL-6, which is involved in human lymphoma, PLZF may have a role in proliferation, differentiation and survival of hematopoietic cells, that could be mediated by transcriptional repression of the cyclin A gene.


METHODS
Quantitative competitive reverse transcription-polymerase chain reaction was used to measure the levels of expression of PLZF and cyclin A in normal leukocyte subsets (including CD19(+) lymphocytes, n=21) and malignant B lymphocytes (including B-chronic lymphocytic leukemias [B-CLL], n=63). Results obtained with this method were confirmed by Western and Northern blot analysis. Transactivation assays were performed using an expression construct for PLZF and two cyclin A promoter luciferase reporters in an Epstein-Barr virus (EBV)-transformed B-cell line. Cyclin A expression, cell growth kinetics, and cell cycle were analysed in stable clones of the Burkitt lymphoma (BL) B-cell line DG75 with inducible expression of PLZF, generated using the tetracycline-regulated expression system.


RESULTS
Expression of PLZF was 100-fold downregulated in 90% B-CLL (56/63) compared to normal B lymphocytes (P<0.001). B-CLL patients with the highest levels of PLZF had a poorer survival (P<0.013). In transactivation assays, PLZF inhibited the activity of the cyclin A reporters by 50%, demonstrating that PLZF can repress cyclin A expression in non-malignant B lymphocytes. However, in B-CLL patients, the level of cyclin A expression was found to be within the normal range. Altered PLZF function in B lymphoid malignancies was further corroborated in the PLZF-regulatable DG75 clones, where induction of PLZF expression did not significantly alter the levels of cyclin A expression, the cell growth kinetics, or the cell cycle phase distribution.


CONCLUSIONS
The lower survival of patients with the highest levels of PLZF suggests that this protein may be a marker of progression in B-CLL. The absence of co-ordinated regulation of PLZF and cyclin A genes in B-CLL and in a malignant B-cell line may indicate a loss of cyclin A control by PLZF in B-CLL and other B-cell disorders. Deregulation of PLZF could thus play a role in B-cell malignancy.
Parrado
A
A
Laboratoire de Biologie Cellulaire Hématopoïétique, Université Paris 7, France. a.parrado@chu-stlouis.fr
Noguera
M E
ME
Delmer
A
A
McKenna
S
S
Davies
J
J
Le Gall
I
I
Bentley
P
P
Whittaker
J A
JA
Sigaux
F
F
Chomienne
C
C
Padua
R A
RA
D015703:Antigens, CD / Q000097:blood; D001483:Base Sequence; D019925:Cyclin A / Q000235:genetics*; D017931:DNA Primers; D004268:DNA-Binding Proteins / Q000235:genetics*; D005091:Exons; D015972:Gene Expression Regulation, Neoplastic; D018922:HL-60 Cells; D006412:Hematopoietic Stem Cells / Q000502:physiology; D006801:Humans; D051741:Kruppel-Like Transcription Factors; D015451:Leukemia, Lymphocytic, Chronic, B-Cell / Q000097:blood / Q000235:genetics*; D016131:Lymphocyte Subsets / Q000276:immunology; D000075722:Promyelocytic Leukemia Zinc Finger Protein; D012333:RNA, Messenger / Q000235:genetics / Q000302:isolation & purification; D020133:Reverse Transcriptase Polymerase Chain Reaction; D014157:Transcription Factors / Q000235:genetics*; D015533:Transcriptional Activation; D014407:Tumor Cells, Cultured; D016335:Zinc Fingers
D015703:Antigens, CD; D019925:Cyclin A; D017931:DNA Primers; D004268:DNA-Binding Proteins; D051741:Kruppel-Like Transcription Factors; D000075722:Promyelocytic Leukemia Zinc Finger Protein; D012333:RNA, Messenger; D014157:Transcription Factors; C092037:ZBTB16 protein, human