Alteration of nuclear factor-kappa B (NF-kappa B) expression in bone marrow stromal cells treated with etoposide

Bone marrow stromal cells are an essential regulatory component in the hema topoietic microenvironment. Regulation of hematopoietic cell development is mediated, in part, through interaction of progenitor cells with stromal ce ll vascular cell adhesion molecule-1 (VCAM-1). VCAM-1 expression has been s hown to be driven primarily by binding of nuclear factor-kappaB (NF-kappaB) to two consensus binding sites in the promoter region, In this study, we s how that down-regulation of VCAM-1 by the chemotherapeutic agent etoposide (VP-16) is associated with altered cellular localization of NF-kappaB. We d emonstrated that VCAM-1 was diminished at the transcriptional level followi ng treatment of stromal cells with VP-16, without alteration of VCAM-1 stab ility. Culture of bone marrow stromal cells in VP-16 resulted in reduced nu clear RelA (p65), a modest increase in nuclear NF-kappa B1 (p50), and reduc ed NF-kappaB binding to its DNA consensus sequence. Total levels of the NF- kappaB inhibitor I kappa -B alpha were reduced during exposure to VP-16. Fo llowing removal of VP-16 from the culture, p65 and p50 nuclear profiles app roximated those of untreated stromal cells, and VCAM-1 protein expression w as restored. The current study indicates that NF-kappaB is a target molecul e that is responsive to VP-16-induced damage in bone marrow stromal cells. As the primary transcription factor that promotes VCAM-1 expression, the ob served changes in p65 and p50 cellular localization during treatment have a direct consequence for stromal cell function. The myriad of genes regulate d by NF-kappaB, including both adhesion molecules and cytokines that contri bute to stromal cell function, make chemotherapy-induced disruption of NF-k appaB biologically significant. Alterations in NF-kappaB activity may provi de one measure by which the effects of aggressive treatment strategies on t he bone marrow microenvironment can be evaluated. (C) 2001 Elsevier Science Inc. Ail rights reserved.