Abstract
We analyzed the intranuclear dynamics of estrogen receptor α (ERα) and progesterone receptor (PR)‐A/B labeled with different spectral variants of green fluorescent protein (GFP) in living cells. The distribution of ERα and PR‐A/B were changed from a diffuse to discrete pattern after the addition of both ligands, but the extent of discrete cluster formation of PR‐A/B was lower than that of ERα. The nuclear areas where PR‐A/B were accumulated were colocalized with the cluster of ERα, suggesting that cross‐talk in the transcriptional regulation occurred in the loci. Fluorescence recovery after photobleaching (FRAP) analysis revealed that the mobility of PR‐A/B was hastened by the coexistence of ERα, while the mobility of ERα was not changed by the coexistence of PR‐A/B. Cluster formation was correlated with the nuclear matrix binding, because nuclear matrix binding capacity was also lower in PR‐A/B than ERα. By ATP‐depletion from the cells, most of ERα and PR‐A/B were bound to the nuclear matrix and their mobilities were extinguished both in the absence and presence of ligand. Fluorescent protein (FP) tagged nuclear matrix component protein (NuMA), which was colocalized with ERα and PR‐A/B, showed ATP‐dependent rapid exchange in the nucleus. These results indicate that the mobility of ERα and PR‐A/B is associated with the dynamics of the nuclear matrix. J. Cell. Biochem. 103: 136–148, 2008. © 2007 Wiley‐Liss, Inc.