Induction of B-chronic lymphocytic leukemia cell apoptosis by arsenic trioxide involves suppression of the phosphoinositide 3-kinase/Akt survival pathway via c-jun-NH2 terminal kinase activation and PTEN upregulation.

PURPOSE: Arsenic trioxide (ATO) induces B-cell chronic lymphocytic leukemia (B-CLL) cell apoptosis in vitro. We sought to study the mechanism involved in this effect and whether ATO is suitable for combination therapies with protein kinase inhibitors. EXPERIMENTAL DESIGN: B-CLL cells were isolated from the peripheral blood of 28 patients. Cell viability studies with ATO alone or in combination with kinase inhibitors were done by flow cytometry, Western blotting, and immunofluorescence analyses. RESULTS: After 48 hours, 3 mumol/L ATO induced apoptosis (average 75%) in all B-CLL samples studied and with minimal effect on normal peripheral blood lymphocytes. Apoptosis entailed Akt and NF-kappaB inactivation, XIAP downregulation, and PTEN upregulation, thus implying inhibition of the phosphoinositide 3-kinase (PI3K) survival pathway. Indeed, the combination of ATO and PI3K inhibitors increased the apoptotic effect of either agent alone. ATO also induced c-jun-NH(2) terminal kinase (JNK) activation, and this was crucial and required for subsequent apoptotic events, as inhibiting JNK activity by either gene silencing or specific inhibitors prevented Akt and NF-kappaB inactivation, caspase activation, and mitochondrial damage. Moreover, JNK activation was the earliest response to ATO, preceding and determining reactive oxygen species production. CONCLUSIONS: We identified the mechanism involved in ATO action on B-CLL cells and show that the combination of low doses of ATO and PI3K inhibitors efficiently induces B-CLL cell death. ATO may therefore constitute an efficient treatment for B-CLL, particularly in combined therapies.

Matrix metalloproteinase-9 promotes chronic lymphocytic leukemia b cell survival through its hemopexin domain.

Matrix metalloproteinase-9 (MMP-9) is the major MMP produced by B-CLL cells and contributes to their tissue infiltration by degrading extracellular and membrane-anchored substrates. Here we describe a different function for MMP-9 in B-CLL, which involves the hemopexin domain rather than its catalytic function. Binding of soluble or immobilized (pro)MMP-9, a catalytically inactive proMMP-9 mutant, or the MMP-9 hemopexin domain to its docking receptors alpha4beta1 integrin and CD44v, induces an intracellular signaling pathway that prevents B-CLL apoptosis. This pathway is induced in all B-CLL cases, is active in B-CLL lymphoid tissues, and consists of Lyn activation, STAT3 phosphorylation, and Mcl-1 upregulation. Our results establish that MMP/receptor binding induces intracellular survival signals and highlight the role of (pro)MMP-9 in B-CLL pathogenesis.

The heparin III-binding domain of fibronectin (III4-5 repeats) binds to fibronectin and inhibits fibronectin matrix assembly.

Fibronectin matrix assembly involves interactions among various regions of the molecule, which contribute to elongation and stabilization of the fibrils. In this study, we examined the possible role of the heparin III domain of fibronectin (repeats III4-5) in fibronectin fibrillogenesis. We show that a recombinant fragment comprising these repeats (FNIII4-5 fragment) blocked fibronectin fibril formation and the incorporation of 125I-fibronectin into cell layers. Binding assays using a biosensor revealed that FNIII4-5 bound fibronectin and the amino-terminal 70 kDa and 29 kDa fragments. It also bound to itself, indicating a previously unidentified self-association site in repeats III4-5. These interactions were specific since FNIII4-5 did not bind to the FNIII7-10 fragment, representing a central region in fibronectin. The fibronectin-binding property of the III4-5 domain, but not its matrix assembly inhibitory function, was apparently cryptic in larger fragments. By mutating the arginine residues in the WTPPRAQITGYRLTVGLTRR proteoglycan-binding sequence (HBP/III5 site) of FNIII4-5 [Moyano, J.V., Carnemolla, B., Albar, J.P., Leprini, A., Gaggero, B., Zardi, L., Garcia-Pardo, A., 1999. Cooperative role for activated alpha4beta1 integrin and chondroitin sulfate proteoglycans in cell adhesion to the heparin III domain of fibronectin. Identification of a novel heparin and cell binding sequence in repeat III5. J. Biol. Chem. 274, 135-142.], we found that the first two arginine residues in HBP/III5 were involved in the fibronectin-binding property of FNIII4-5, while the last two arginine residues in HBP/III5 were required for inhibition of matrix assembly and the binding of 125I-fibronectin to cell layers. Both properties appear to function independently from each other, depending on the conformation of the fibronectin dimer.

Involvement of p53 in alpha4beta1 integrin-mediated resistance of B-CLL cells to fludarabine.

We recently showed that alpha4beta1 integrin induces B-cell chronic lymphocytic leukemia (B-CLL) cell resistance to fludarabine-induced apoptosis via upregulation of Bcl-xL. We have now studied whether p53 was involved in this response. Cells from five B-CLL patients with wild-type p53 determined by DNA sequencing, or from the EHEB cell line, cultured on the alpha4beta1 ligand H/89 during fludarabine treatment, showed significantly higher viability (P