Targeting BCL-2 overexpression in various human malignancies through NF-kappaB inhibition by the proteasome inhibitor bortezomib.
BACKGROUND
BCL-2 overexpression occurs in many cancer types and is associated with chemoresistance and radioresistance. The mechanisms responsible for its aberrant expression are thought to be transcriptionally mediated but remain unclear. We examined the cell type-specific mechanism of BCL-2 gene transcription in various solid organ malignancies.


METHODS
Regulation of BCL-2 gene transcription was examined in seven different human cancer cell lines including two pancreatic (MIA-PaCa-2, PANC-1), two prostate (LNCaP, PC-3), two lung (Calu-1, A549) and one breast (MCF-7) cancer cell line. Cells were treated with inhibitors of phosphatidylinositol-3 kinase (PI3K), MEK/ERK, and p38MAPK. The effect of mutation of a NF-kappaB site in the BCL-2 promoter was determined, as was the effect of inhibition of NF-kappaB function using a 26S proteasome inhibitor (bortezomib) on both BCL-2 transcription and induction of apoptosis.


RESULTS
BCL-2 expression varied both between and within tumor types; four of seven cell lines demonstrated high BCL-2 levels (MIA-PaCa-2, PC-3, Calu-1 and MCF-7). No signaling pathway was uniformly responsible for overexpression of BCL-2; however, mutation of the NF-kappaB site decreased BCL-2 promoter activity in all cell lines. Inhibition of NF-kappaB activity decreased BCL-2 protein levels independently of the signaling pathway involved in transcriptional activation of the BCL-2 gene.


CONCLUSIONS
Diverse signaling pathways variably regulate BCL-2 gene expression in a cell type-specific fashion. Therapy to decrease BCL-2 levels in various human cancers would be more broadly applicable if targeted to transcriptional activation rather than signal transduction cascades. Finally, the apoptotic efficacy of proteasome inhibition with bortezomib paralleled the ability to inhibit NF-kappaB activity and decrease BCL-2 levels.
Fahy
Bridget N
BN
Division of Surgical Oncology, University of California Davis Cancer Center, Sacramento, CA 95817, USA.
Schlieman
Michael G
MG
Mortenson
Melinda M
MM
Virudachalam
Subbulakshmi
S
Bold
Richard J
RJ
D001897:Boronic Acids / Q000494:pharmacology*; D000069286:Bortezomib; D001943:Breast Neoplasms / Q000473:pathology*; D019938:Cyclin D1 / Q000096:biosynthesis*; D005260:Female; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects*; D006801:Humans; D008297:Male; D016328:NF-kappa B / Q000037:antagonists & inhibitors / Q000494:pharmacology*; D010190:Pancreatic Neoplasms / Q000473:pathology*; D011471:Prostatic Neoplasms / Q000473:pathology*; D011480:Protease Inhibitors / Q000494:pharmacology*; D011719:Pyrazines / Q000494:pharmacology*; D015398:Signal Transduction; D014158:Transcription, Genetic; D014407:Tumor Cells, Cultured
D001897:Boronic Acids; D016328:NF-kappa B; D011480:Protease Inhibitors; D011719:Pyrazines; D019938:Cyclin D1; D000069286:Bortezomib