Microtubule‐dependent nuclear‐cytoplasmic shuttling of Runx2

Abstract

RUNX/AML transcription factors are critical regulators of cell growth and differentiation in multiple lineages and have been linked to human cancers including acute myelogenous leukemia (RUNX1), as well as breast (RUNX2) and gastric cancers (RUNX3). RUNX proteins are targeted to gene regulatory micro-environments within the nucleus via a specific subnuclear targeting signal. However, the dynamics of RUNX distribution and compartmentalization between the cytoplasm and nucleus is minimally understood. Here we show by immunofluorescence microscopy that RUNX2 relocates from the nucleus to the cytoplasm when microtubules are stabilized by the chemotherapeutic agent taxol. The taxol-dependent cytoplasmic accumulation of RUNX2 is inhibited by leptomycin B, which blocks CRM-1 dependent nuclear export, and is not affected by the protein synthesis inhibitor cycloheximide. Using biochemical assays, we show that endogenous RUNX2 associates with stabilized microtubules in a concentration-dependent manner and that the RUNX2 amino terminus mediates the microtubule association. In soluble fractions of cells, RUNX2 co-immunoprecipitates alpha tubulin suggesting that microtubule binding involves the alpha/beta tubulin subunits. We conclude that RUNX2 associates with microtubules and shuttles between the nucleus and the cytoplasm. We propose that nuclear-cytoplasmic shuttling of RUNX2 may modulate its transcriptional activity, as well as its ability to interface with signal transduction pathways that are integrated at RUNX2 containing subnuclear sites. It is possible that taxol-induced acute depletion of the nuclear levels of RUNX2 and/or other cell growth regulatory factors may represent an alternative pathway by which taxol exerts its biological effects during cancer chemotherapies.

Mitotic retention of gene expression patterns by the cell fate-determining transcription factor Runx2

“…Although Runx2 is localized with mitotic chromosomes, a fraction of Runx2 is extrachromosomal, perhaps in association with microtubules (ref. 34 and our unpublished observations). Our conclusion that Runx2 associates with mitotic chromosomes is based on both microscopic evidence ( Fig.…”

NAA10 controls osteoblast differentiation and bone formation as a feedback regulator of Runx2

“…18c,d). These results suggest that Runx2 is targeted by NAA10 in the cytoplasm before it enters into the nucleus or while it shuttles between the nucleus and the cytoplasm 23 . To identify the entity responsible for the reversal of the NAA10-mediated acetylation of the RUNT domain, we searched for the deacetylase among HDAC members.…”

The microtubule-associated protein DCAMKL1 regulates osteoblast function via repression of Runx2

“…In contrast, a truncated DCAMKL1 mutant containing mutant, or a control GFP expression vector were transfected into cells expressing myc epitope-tagged Runx2. Analysis of cells transfected with the control GFP expression vector revealed that Runx2 localization was predominantly nuclear sequestration of Runx2 (Pockwinse et al, 2006), we questioned whether DCAMKL1 may repress Runx2 transcriptional activity through sequestering Runx2 in the cytoplasm. To assess this, GFP-tagged DCAMKL1, GFP-tagged DCL WT and Dcamkl1 / mice.…”