Physical and Functional Interaction between Heterochromatin Protein 1α and the RNA-binding Protein Heterogeneous Nuclear Ribonucleoprotein U

By combining biochemical purification and mass spectrometry, we identified proteins associated with human heterochromatin protein 1 alpha (HP1 alpha) both in the nucleoplasm and in chromatin. Some of these are RNA-binding proteins, and among them is the protein heterogeneous nuclear ribonucleoprotein U (hnRNP U)/SAF-A, which is linked to chromatin organization and transcriptional regulation. Here, we demonstrate that hnRNP U is a bona fide HP1 alpha-interacting molecule. More importantly, hnRNP U depletion reduces HP1 alpha-dependent gene silencing and disturbs HP1 alpha subcellular localization. Thus, our data demonstrate that hnRNP U is involved in HP1 alpha function, shedding new light on the mode of action of HP1 alpha and on the function of hnRNP U.