Microtubule Disruption Utilizes an NFB-dependent Pathway to Stabilize HIF-1 Protein^*

Yun-Jin Jung, Jennifer S. Isaacs, Sunmin Lee^§, Jane Trepel^§, and Len Neckers^¶

From the  Cell and Cancer Biology Branch, Center for Cancer Research, NCI, National Institutes of Health, Rockville, Maryland 20850 and the ^§ Medical Oncology Clinical Research Unit, CCR, NCI, National Institutes of Health, Bethesda, Maryland 20892

Hypoxia-inducible factor (HIF)-1 levels are elevated in normoxic cells undergoing physiological processes involving large scale microtubule reorganization, such as embryonic development, wound healing, and tumor cell metastasis. Although alterations in microtubules affect numerous cellular responses, no data have yet implicated microtubule dynamics in HIF-1 regulation. To investigate the effect of microtubule change upon HIF-1 regulation, we treated cells with the microtubule-depolymerizing agents (MDAs) colchicine, vinblastine or nocodazole. We demonstrate that these agents are able to induce transcriptionally active HIF-1. MDA-mediated induction of HIF-1 required microtubule depolymerization, since HIF-1 levels were unchanged in cells treated with either the microtubule-stabilizing agent paclitaxel, or an inactive form of colchicine, or in colchicine-resistant cells. HIF-1 induction was dependent upon cellular transcription, as transcription inhibitors abrogated HIF-1 protein up-regulation. The ability of transcriptional inhibitors to interfere with HIF-1 accumulation was specific to the MDA-initiated pathway, as they were ineffective in preventing hypoxia-mediated HIF-1 induction, which occurs by a distinct post-translational pathway. Moreover, we provide evidence implicating a requirement for NFB transcription in the HIF-1 induction mediated by MDAs. The ability of MDAs to induce HIF-1 is dependent upon activation of NFB, since inhibition of NFB either pharmacologically or by transfection of an NFB super-repressor plasmid abrogated this induction. Collectively, these data support a model in which NFB is a focal point for the convergence of MDA-mediated signaling events leading to HIF-1 induction, thus revealing a novel aspect of HIF-1 regulation and function.