Subnuclear Localization of C/EBP Is Regulated by Growth Hormone and Dependent on MAPK*

Localization of transcription regulatory proteins in the nucleus is dynamically regulated, and may alter nu-cleoplasmic concentrations and/or assembly of multimo-lecular transcription regulatory complexes, which ulti-mately regulate gene expression. Since growth hormone (GH) regulates multiple transcription factors including C/EBP, the effect of GH on the subcellular localization of C/EBP was examined in 3T3-F442A preadipocytes. Indirect immunofluorescence shows that C/EBP is dif-fusely distributed in nuclei of quiescent cells. Within 5 min of GH treatment, the diffuse pattern dramatically becomes punctate. The relocalization of C/EBP coin-cides with DAPI staining of heterochromatin. Further, C/EBP and heterochromatin protein (HP)-1 colocalize in the nucleus, consistent with localization of C/EBP t