title: Thymosin beta 4 may translocate from the cytoplasm in to the nucleus in HepG2 cells following serum starvation. An ultrastructural study.
abstract: Due to its actin-sequestering properties, thymosin beta-4 (Tβ4) is considered to play a significant role in the cellular metabolism. Several physiological properties of Tβ4 have been reported;, however, many questions concerning its cellular function remain to be ascertained. To better understand the role of this small peptide we have analyzed by means of transmission immunoelectron microscopy techniques the ultrastructural localization of Tβ4 in HepG2 cells. Samples of HepG2 cells were fixed in a mixture of 3% formaldehyde and 0.1% glutaraldehyde in 0.1 M cacodylate buffer and processed for standard electron microscopic techniques. The samples were dehydrated in a cold graded methanol series and embedded in LR gold resin. Ultrathin sections were labeled with rabbit antibodies to Tβ4, followed by gold-labeled goat anti-rabbit, stained with uranyl acetate and bismuth subnitrate, observed and photographed in a JEOL 100S transmission electron microscope. High-resolution electron microscopy showed that Tβ4 was mainly restricted to the cytoplasm of HepG2 growing in complete medium. A strong Tβ4 reactivity was detected in the perinuclear region of the cytoplasmic compartment where gold particles appeared strictly associated to the nuclear membrane. In the nucleus specific Tβ4 labeling was observed in the nucleolus. The above electron microscopic results confirm and extend previous observations at light microscopic level, highlighting the subcellular distribution of Tβ4 in both cytoplasmic and nuclear compartments of HepG2 cells. The meaning of Tβ4 presence in the nucleolus is not on the best of our knowledge clarified yet. It could account for the interaction of Tβ4 with nucleolar actin and according with this hypothesis, Tβ4 could contribute together with the other nucleolar acting binding proteins to modulate the transcription activity of the RNA polymerases.
authors.affiliation: Department of Biomedical Sciences, University of Cagliari, Cagliari, Italy.
authors.forename: Marco
authors.initials: M
authors.lastname: Piludu
authors.affiliation: Divisione di Anatomia Patologica, Dipartimento di Citomorfologia, University of Cagliari, Cagliari, Italy.
authors.forename: Monica
authors.initials: M
authors.lastname: Piras
authors.affiliation: Divisione di Anatomia Patologica, Dipartimento di Citomorfologia, University of Cagliari, Cagliari, Italy.
authors.forename: Giuseppina
authors.initials: G
authors.lastname: Pichiri
authors.affiliation: Divisione di Anatomia Patologica, Dipartimento di Citomorfologia, University of Cagliari, Cagliari, Italy.
authors.forename: Pierpaolo
authors.initials: P
authors.lastname: Coni
authors.affiliation: OBL, Department of Surgical Sciences, University of Cagliari, Cagliari, Italy.
authors.forename: Germano
authors.initials: G
authors.lastname: Orrù
authors.affiliation: Dipartimento di Scienze della Vita e dell'Ambiente, Universitadi Cagliari, Cagliari, Italy.
authors.forename: Tiziana
authors.initials: T
authors.lastname: Cabras
authors.affiliation: Dipartimento di Scienze della Vita e dell'Ambiente, Universitadi Cagliari, Cagliari, Italy.
authors.forename: Irene
authors.initials: I
authors.lastname: Messana
authors.affiliation: Divisione di Anatomia Patologica, Dipartimento di Citomorfologia, University of Cagliari, Cagliari, Italy.
authors.forename: Gavino
authors.initials: G
authors.lastname: Faa
authors.affiliation: Istituto di Biochimica e di Biochimica Clinica, Universita`Cattolica, Roma, Italy; Istituto per la Chimica del Riconoscimento Molecolare, CNR, IstitutoScientifico, Internazionale (ISI) Paolo VI, Roma, Italy.
authors.forename: Massimo
authors.initials: M
authors.lastname: Castagnola
mesh_terms: D002467:Cell Nucleus / Q000378:metabolism / Q000648:ultrastructure; D003593:Cytoplasm / Q000378:metabolism / Q000648:ultrastructure; D015870:Gene Expression; D056945:Hep G2 Cells; D006801:Humans; D021381:Protein Transport; D013947:Thymosin / Q000235:genetics / Q000378:metabolism*; D000099201:Thymosin beta(4)
chemical_list: D013947:Thymosin; D000099201:Thymosin beta(4)
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