ASH: ZAP-70 May Help Activate NFkB; Therapeutic Intervention May Be Possible

[Guest guest]

[2812] Expression of ZAP-70 in B Cell Chronic Lymphocytic Leukemia Is

Associated with a Greater Capacity To Activate NF & #954;B Following Ligation

of Surface Immunoglobulin. Session Type: Poster Session 82-III

Januario E. Castro, E. Prada, Jorieth M. , A. Jung,

Liguang J. Chen, A. Meraz, J. Kipps. and

s Cancer Center, University of California-San Diego, La Jolla,

CA, USA; Chronic lymphocytic leukemia Research Consortium (CRC), San

Diego, CA, USA

The NF & #954;B transcription factors p50/p65 regulate the expression of

genes encoding various growth-promoting factors and anti-apoptotic

proteins, such as the cellular inhibitors of apoptosis (c-IAPs),

Caspase-8/Flice-inhibitory protein (FLIP), A1 (also known as Bfl1),

tumor necrosis factor receptor (TNFR)-associated factor 1 (TRAF1) and

2 (TRAF2). Furthermore, constitutive activation of NF & #954;B has been

observed in many tumor types, supporting the notion that activation of

NF & #954;B can play a causal role in tumor development and/or progression.

Studies have shown chronic lymphocytic leukemia (CLL) cells experience

activation of NF & #954;B in vitro upon ligation of their surface

immunoglobulin (Ig), which commonly possesses polyreactive-binding

activity for many self-antigens. Other studies also have found that

CLL cells from different patients vary in their capacity to undergo

B-cell-receptor signaling following ligation of their surface Ig

receptors, a capacity that appears associated with leukemia-B-cell

expression of the zeta-associated protein of 70 kD (ZAP-70).

We examined whether CLL B cell expression of ZAP-70 also was

associated with the capacity to activate NF & #954;B upon surface Ig

ligation. For this we used CLL B cells of 8 different patients that

expressed ZAP-70 and CLL B cells from 8 other patients that had

negligible expression of this tyrosine kinase (as assessed by

immunoblot and flow cytometric analysis).

The CLL B cells of these two groups of patients had similar expression

levels of surface, allowing us to use a F(ab')2 anti-human IgM

(anti-µ) to effect comparable surface Ig receptor ligation. Following

treatment with anti-µ, we observed early and sustained degradation of

I & #954;B- & #945;, thereby releasing cytoplasmic p50/p65 to the nucleus - the

hallmark of NF & #954;B activation. Moreover, this was associated with

subsequent increased expression of NF & #954;B target genes.

In contrast, similar events were not observed following treatment with

anti-µ in the cases lacking expression of ZAP-70. Also, activation of

NF & #954;B in ZAP-70+ cases was associated with a greater release of

intracellular calcium and calcium flux following treatment with anti-µ

than observed in ZAP-70-negative cases. Both calcium flux and

activation of NF & #954;B induced by anti-µ in these leukemia cells could be

inhibited by Cyclosporine-A, indicating that these responses were

mediated via a calmodulin-calcineurin-dependent pathway.

These studies reveal that expression of ZAP-70 in B cell CLL is

associated with a greater capacity to induce activation of NF & #954;B

following ligation of surface Ig, a characteristic that might account

for the more aggressive clinical behavior of patients with leukemia B

cells that express this tyrosine kinase.

Moreover, if constitutive activation via ligation of surface Ig with

self-antigen in vivo leads to activation of NF & #954;B, then targeting the

calmodulin-calcineurin-dependent pathway might have therapeutic

potential for this subset of patients with this disease.

Abstract #2812 appears in Blood, Volume 103, issue 12, November 16, 2004

Keywords: Signal transduction|Leukemia|ZAP-70

Monday, December 6, 2004, 5:30 PM

Poster Session: CLL - Biology and Clinical Investigation, Excluding

Therapy III (5:30 PM-7:00 PM)