title: Variant-specific patterns and humoral regulation of HP1 proteins in human cells and tissues.
abstract: We have examined the occurrence and distribution of HP1alpha and HP1beta under in vivo, ex vivo and in vitro conditions. Consistent with a non-essential role in heterochromatin maintenance, both proteins are diminished or undetectable in several types of differentiated cells and are universally downregulated during erythropoiesis. Variant-specific patterns are observed in almost all human and mouse tissues examined. Yet, the most instructive example of HP1 plasticity is observed in the lymph nodes, where HP1alpha and HP1beta exhibit regional patterns that are exactly complementary to one another. Furthermore, whereas HP1alpha shows a dispersed sub-nuclear distribution in the majority of peripheral lymphocytes, it coalesces into large heterochromatic foci upon stimulation with various mitogens and IL-2. The effect of inductive signals on HP1alpha distribution is reproduced by coculture of immortalized T- and B-cells and can be confirmed using specific markers. These complex patterns reveal an unexpected plasticity in HP1 variant expression and strongly suggest that the sub-nuclear distribution of HP1 proteins is regulated by humoral signals and microenvironmental cues.
authors.affiliation: Stem Cell and Chromatin Group, Laboratory of Biology, The University of Ioannina School of Medicine, Dourouti, Greece.
authors.forename: Eleni
authors.initials: E
authors.lastname: Ritou
authors.forename: Maria
authors.initials: M
authors.lastname: Bai
authors.forename: Spyros D
authors.initials: SD
authors.lastname: Georgatos
mesh_terms: D000818:Animals; D002478:Cells, Cultured; D000090266:Chromobox Protein Homolog 5; D002868:Chromosomal Proteins, Non-Histone / Q000235:genetics / Q000378:metabolism*; D004920:Erythropoiesis / Q000502:physiology; D006801:Humans; D008198:Lymph Nodes / Q000166:cytology / Q000378:metabolism; D008213:Lymphocyte Activation; D008214:Lymphocytes / Q000166:cytology / Q000378:metabolism; D051379:Mice; D020033:Protein Isoforms / Q000235:genetics / Q000378:metabolism*; D014018:Tissue Distribution
chemical_list: C000715593:CBX1 protein, human; C000715594:CBX5 protein, human; D002868:Chromosomal Proteins, Non-Histone; D020033:Protein Isoforms; D000090266:Chromobox Protein Homolog 5