Coordinate modulation of Sp1, NF‐kappa B, and p53 in confluent human malignant melanoma cells after ionizing radiation

Abstract

Regulation of transcriptional responses in growth-arrested human cells under conditions that promote potentially lethal damage repair after ionizing radiation (IR) is poorly understood. Sp1/retinoblastoma control protein (RCP) DNA binding increased within 30 min and peaked at 2-4 h after IR (450-600 cGy) in confluent radioresistant human malignant melanoma (U1-Mel) cells. Increased phosphorylation of Sp1 directly corresponded to Sp1/RCP binding and immediate-early gene induction, whereas pRb remained hypophosphorylated. Transfection of U1-Mel cells with the human papillomavirus E7 gene abrogated Sp1/RCP induction and G(0)/G(1) cell cycle checkpoint arrest responses, increased apoptosis and radiosensitivity, and augmented genetic instability (i.e., increased polyploidy cells) after IR. Increased NF-kappaB DNA binding in U1-Mel cells after IR treatment lasted much longer (i.e., >20 h). U1-Mel cells overexpressing dominant-negative IkappaBalpha S32/36A mutant protein were significantly more resistant to IR exposure and retained both G(2)/M and G(0)/G(1) cell cycle checkpoint responses without significant genetic instability (i.e., polyploid cell populations were not observed). Nuclear p53 protein levels and DNA binding activity increased only after high doses of IR (>1200 cGy). Disruption of p53 responses in U1-Mel cells by E6 transfection also abrogated G(0)/G(1) cell cycle checkpoint arrest responses and increased polyploidy after IR, but did not alter radiosensitivity. These data suggest that abrogation of individual components of this coordinate IR-activated transcription factor response may lead to divergent alterations in cell cycle checkpoints, genomic instability, apoptosis, and survival. Such coordinate transcription factor activation in human cancer cells is reminiscent of prokaryotic SOS responses, and further elucidation of these events should shed light on the initial molecular events in the chromosome instability phenotype.-Yang, C.-R., Wilson-Van Patten, C., Planchon, S. M., Wuerzberger-Davis, S. M., Davis, T. W., Cuthill, C., Miyamoto, S., Boothman, D. A. Coordinate modulation of Sp1, NF-kappa B, and p53 in confluent human malignant melanoma cells after ionizing radiation.

Oxidative Stress Induces Premature Senescence by Stimulating Caveolin-1 Gene Transcription through p38 Mitogen-Activated Protein Kinase/Sp1–Mediated Activation of Two GC-Rich Promoter Elements

“…Transcription factors belonging to the Sp family are known to bind to GC-rich boxes. The family member Sp1 has been shown to mediate oxidative stress-induced gene transcription (38)(39)(40). Thus, we decided to look at whether Sp1 may represent the transcription factor that activates the caveolin-1 gene after oxidative stress.…”

Arsenic trioxide prevents radiation-enhanced tumor invasiveness and inhibits matrix metalloproteinase-9 through downregulation of nuclear factor κB

“…The activation of NF-kB mediates the synthesis of inflammatory cytokines (Zhou et al, 2001) and the modulation of radiosensitivity. Several studies suggested that NF-kB promoted radiosensitivity (Yang et al, 2000); however, accumulating evidences demonstrated that radiosensitization can be achieved by inhibiting NF-kB activation in many cancer cell types (Yamagishi et al, 1997;Eichholtz-Wirth and Sagan, 2000;Kato et al, 2000;Didelot et al, 2001;Russo et al, 2001). Consistent with these observations, the inhibition of radiation-mediated NF-kB activation directly suppressed MMP-9 synthesis and activity, which contributes to arsenic-inhibited tumor invasion and metastasis.…”

NF-κB, chemokine gene transcription and tumour growth

“…Treatment of human malignant melanoma cells with ionizing radiation induces the coordinated activation of NF-κB and other regulators of transcription 24 . The activation of NF-κB correlates with CXCL8 expression, growth, angiogenesis and metastasis of human melanoma cells 25,26 .…”