ZAP-70 tyrosine kinase is constitutively expressed and phosphorylated in B-lineage acute lymphoblastic leukemia cells.
OBJECTIVE
Zeta-associated protein 70 (ZAP-70), a member of the Syk family of protein tyrosine kinases, is normally expressed in T and NK cells. While little is known about ZAP-70 expression in normal human B cells, it has been reported that ZAP-70 is expressed in a subset of patients with chronic lymphocytic leukemia (CLL) with a poor prognosis. In this study, we examined the expression and phosphorylation status of ZAP-70 in B-lineage acute lymphoblastic leukemia (Blin-ALL).


METHODS
First, ZAP-70 protein expression was assessed by Western blotting and flow cytometry and ZAP-70 mRNA transcripts were analyzed by reverse transcription polymerase chain reaction (RT-PCR) on human precursor B cell lines. Experiments were then carried out on cells obtained from 18 patients with Blin-ALL and from normal human bone marrow.


RESULTS
ZAP-70 was constitutively expressed and phosphorylated on tyr319 in human precursor Blin-ALL cell lines as well as in primary B leukemic cells from all examined Blin-ALL patients with pro-B, pre-B and B phenotypes, but not in malignant myeloid cells. Importantly, analysis of normal human bone marrow revealed expression of ZAP-70 transcripts only in the CD34+ cell fraction (either CD19-CD10- or CD19+CD10+) but not in the CD34- cell fraction (CD19+sIgM- pre-B cells or CD19+sIgM+ immature B cells).


CONCLUSIONS
ZAP-70 was found to be expressed in the CD34+ normal bone marrow compartment including earlier B-cell progenitors, but not in CD34- pre-B and immature B cells. By contrast, ZAP-70 was consistently expressed and phosphorylated in Blin-ALL cells. Further studies are required to determine whether ZAP-70 may play a pathophysiological role in Blin-ALL.
Guillaume
Nicolas
N
INSERM E0351, Laboratoire d'Immunologie, Faculté de Médecine, 80 036 Amiens, France.
Alleaume
Céline
C
Munfus
Délicia
D
Capiod
Jean-Claude
JC
Touati
Gilles
G
Pautard
Brigitte
B
Desablens
Bernard
B
Lefrère
Jean-Jacques
JJ
Gouilleux
Fabrice
F
Lassoued
Kaiss
K
Gouilleux-Gruart
Valérie
V
D000328:Adult; D018952:Antigens, CD34 / Q000096:biosynthesis; D001853:Bone Marrow / Q000378:metabolism; D002051:Burkitt Lymphoma / Q000235:genetics* / Q000378:metabolism*; D002648:Child; D002675:Child, Preschool; D005260:Female; D015972:Gene Expression Regulation, Neoplastic; D006801:Humans; D007223:Infant; D008297:Male; D008875:Middle Aged; D010766:Phosphorylation; D051746:ZAP-70 Protein-Tyrosine Kinase / Q000096:biosynthesis* / Q000235:genetics*
D018952:Antigens, CD34; D051746:ZAP-70 Protein-Tyrosine Kinase