Spleen tyrosine kinase (Syk) deficiency in childhood pro-B cell acute lymphoblastic leukemia

Abstract

The cytoplasmic spleen tyrosine kinase (SYK) is a key regulator of signal transduction events, apoptosis and orderly cell cycle progression in B-lineage lymphoid cells. Although SYK has not been linked to a human disease, defective expression of the closely related T-cell tyrosine kinase ZAP-70 has been associated with severe combined immunode®ciency. Childhood CD19 + CD10 7 pro-B cell acute lymphoblastic leukemia (ALL) is thought to originate from B-cell precursors with a maturational arrest at the pro-B cell stage and it is associated with poor prognosis. Since lethally irradiated mice reconstituted with SYK-de®cient fetal liver-derived lymphohematopoietic progenitor cells show a block in B-cell ontogeny at the pro-B to pre-B cell transition, we examined the SYK expression pro®les of primary leukemic cells from children with pro-B cell ALL. Here we report that leukemic cells from pediatric CD19 + CD10 7 pro-B cell ALL patients (but not leukemic cells from patients with CD19 + CD10 + common pre-pre-B cell ALL) have markedly reduced SYK activity. Sequencing of the reverse transcriptase-polymerase chain reaction (RT ± PCR) products of the Syk mRNA in these pro-B leukemia cells revealed profoundly aberrant coding sequences with deletions or insertions. These mRNA species encode abnormal SYK proteins with a missing or truncated catalytic kinase domain. In contrast to pro-B leukemia cells, pre-pre-B leukemia cells from children with CD19 + CD10 + common Blineage ALL and EBV-transformed B-cell lines from healthy volunteers expressed wild-type Syk coding sequences. Examination of the genomic structure of the Syk gene by inter-exonic PCR and genomic cloning demonstrated that the deletions and insertions in the abnormal mRNA species of pro-B leukemia cells are caused by aberrant splicing resulting in either missplicing, exon skipping or inclusion of alternative exons, consistent with an abnormal posttranscriptional regulation of alternative splicing of Syk pre-mRNA. Our ®ndings link for the ®rst time speci®c molecular defects involving the Syk gene to an immunophenotypically distinct category of childhood ALL. To our knowledge, this is the ®rst discovery of a speci®c tyrosine kinase de®ciency in a human hematologic malignancy. Oncogene (2001) 20, 3969 ± 3978.

Hypermethylation of the spleen tyrosine kinase promoter in T-lineage acute lymphoblastic leukemia

“…Further studies are necessary to determine the exact prevalence and clinical significance of Syk promoter methylation in T-lineage ALL. Since we have previously demonstrated aberrant Syk splicing in cases of pro-B lineage ALL (Goodman et al, 2001), these results suggest that SYK may serve as a tumorsuppressor function in leukemia in addition to its previously described role as a tumor suppressor in breast cancer.…”

“…Two Syk cDNA fragments, a nearly full-length 2.2 kb Syk cDNA (108-2265 bp) and a 502 bp ScaI fragment (1095-1597 bp), were used as probes as previously described (Goodman et al, 2001). An oligonucleotide probe, AA (5 0 -CGC CCG CCC TCG CCT CAC CTG GCG C-3 0 ), corresponding to the 5 0 untranslated region of HUMPTK (Accession # L 28824) was synthesized.…”

STAT3 is a substrate of SYK tyrosine kinase in B-lineage leukemia/lymphoma cells exposed to oxidative stress

“…As shown in Fig. 3E and F We next compared the PV-responsiveness of SYK þ RAMOS (26) cells vs. SYK-deficient cells from a proB ALL patient (ProB#4) with a missplicing at the 5′ end of syk exon 5 leading to a 4 bp deletion (Δ½G 865 -G 868 ) in the syk coding sequence that causes a frameshift starting after Trp 239 with absent SYK protein expression and SYK kinase activity (27). Notably, PV [but not CD19 receptor engagement with an anti-CD19 homoconjugate (26)] failed to induce Y-phosphorylation of the STAT3(Y705) phosphoepitope in SYK-deficient ProB#4 cells (Fig.…”

“…Notably, BLNK deficiency plays an important role in the leukemogenesis of B-lineage ALL (52) and a significant portion of B-lineage ALL cases are BLNK-negative (53). The remarkable radiation resistance of relapsed B-lineage ALL patients (pre-pre-B immunophenotype) (6) with abundant expression of SYK (27) indicates that the balance of SYK-linked proapoptotic vs. antiapoptotic signals triggered by OS is an antiapoptotic signal, which may in part be related to their underlying BLNK deficiency. It is noteworthy that SYK also has been reported to have an antiapoptotic function in DT40 cells in the context of ceramide responses that is independent of its enzymatic activity (54).…”

Cytotoxic activity of gemtuzumab ozogamicin (Mylotarg) in acute myeloid leukemia correlates with the expression of protein kinase Syk

“…Significantly greater numbers of Syk/Zap-70-positive samples respond to anti-CD33 mAb treatment. 29 Recent discoveries established Syk as a tumor suppressor and linked deficient Syk expression to a variety of human hematopoietic [30][31][32][33] and solid tumors. [33][34][35] In breast cancer, Syk kinase is a potent modulator of malignant growth and a potential tumor suppressor, presumably by controlling cell division.…”