Inhibition of constitutive NF-kappaB activation in mantle cell lymphoma B cell lead to induction of cell cycle arrest and apoptosis

Pham LV, Tamayo AT, Yoshimura LC, Lo P and Ford RJ
Source: J Immunol
Publication Date: (2003)
Issue: 171: 88-95
Research Area:
Immunotherapy / Hematology
Cells used in publication:
Species: human
Tissue Origin: blood
Mantle cell lymphoma (MCL) is an agressive histotype of B cell non-Hodgkin?s lymphoma (NHL-B), a heterogeneous group of human lymphoid neoplasm. NF-kappaB appears to be pivotally involved in the pathogenesis of aggressive lymphoid malignancies. Normally, NF-kappaB is transcriptionally inactive in the cytoplasm of most cells because it is bound to its cytoplasmic inhibitor IkappaBa. Upon stimulation with proinflammatory cytokines IkappaBa protein is phosphorylated, ubiquitinated and subsequently degraded by proteasome. This allows NF-kappaB translocation into the nucleus and activation of target genes. The authors found that NF-kappaB is constitutively active in MCL cells. To define the importance of NF-kappaB activation on MCL cell growth a dominant-negative version of IkappaBa was nucleofected into MCL cells. NF-kappaB expression was determined by EMSA and cell viability was assessed by trypan blue counting. The findings suggest that constitutive NF-kappaB activation plays a key role in the survival of MCL cells.
Constitutive activation of the NF-kappaB has been documented to be involved in the pathogenesis of many human malignancies, including hemopoietic neoplasms. In this study, we examined the status of NF-kappaB in two non-Hodgkin's lymphoma cell lines derived from mantle cell lymphoma (MCL) samples and in patient MCL biopsy specimens by EMSA and confocal microscopic analysis. We observed that NF-kappaB is constitutively activated in both the MCL cell lines and in the MCL patient biopsy cells. Since NF-kappaB has been shown to play an important role in a variety of cellular processes, including cell cycle regulation and apoptosis, targeting the NF-kappaB pathways for therapy may represent a rational approach in this malignancy. In the MCL cell lines, inhibition of constitutive NF-kappaB by the proteasome inhibitor PS-341 or a specific pIkappaBalpha inhibitor, BAY 11-7082, led to cell cycle arrest in G(1) and rapid induction of apoptosis. Apoptosis was associated with the down-regulation of bcl-2 family members bcl-x(L) and bfl/A1, and the activation of caspase 3, that mediates bcl-2 cleavage, resulting in the release of cytochrome c from the mitochondria. PS-341or BAY 11-induced G(1) cell cycle arrest was associated with the inhibition of cyclin D1 expression, a molecular genetic marker of MCL. These studies suggest that constitutive NF-kappaB expression plays a key role in the growth and survival of MCL cells, and that PS-341 and BAY 11 may be useful therapeutic agents for MCL, a lymphoma that is refractory to most current chemotherapy regimens.