RESEARCH ARTICLE Thymosin Beta 4 May Translocate from the Cytoplasm in to the Nucleus in HepG2 Cells following Serum Starvation. An Ultrastructural Study

Due to its actin-sequestering properties, thymosin beta-4 (Tβ4) is considered to play a sig-nificant role in the cellular metabolism. Several physiological properties of Tβ4 have been reported;, however, many questions concerning its cellular function remain to be ascer-tained. 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 micro-scopic techniques. The samples were dehydrated in a cold graded methanol series and em-bedded 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 subni-trate, 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 perinuc-lear region of the cytoplasmic compartment where gold particles appeared strictly associat