title: Prothymosin alpha is phosphorylated in proliferating stimulated cells.
abstract: Prothymosin alpha is a widely distributed polypeptide whose function, though unknown, seems to be related to cell proliferation. In vitro, it is a substrate for casein kinase-2. In this work, extracts of mitogenically stimulated murine splenic lymphocytes labeled with [32P] orthophosphate were found to contain [32P]prothymosin alpha. Phosphorylation activity was highly dependent on mitogenic activation with concanavalin A plus interleukin-2. While cells remained viable, phosphorylation increased with stimulation time in the presence of [32P]orthophosphate. Structural analysis showed that prothymosin alpha was phosphorylated at Thr residues located among its first 14 amino acids, whereas its in vitro phosphorylation by casein kinase-2 affects both Ser and Thr residues in this fragment, apparently in similar proportions. Thus, casein kinase-2 seems not to be responsible for the phosphorylation of prothymosin alpha in vivo. Prothymosin alpha was also found to be phosphorylated in proliferating murine thymocytes and HeLa cells; the phosphorylation sites were the same as in splenic lymphocytes, but the rate of phosphorylation was about 5 times lower. In thymocytes and subconfluent HeLa cells, the [32P]prothymosin alpha concentrations of the cytosolic and nuclear fractions were similar; in splenic lymphocytes, [32P]prothymosin alpha was found mostly in cytosol.
authors.affiliation: Departamento de Bioquimica e Bioloxia Molecular, Facultade de Bioloxia, Universidade de Santiago, Santiago de Compostela, Galicia, Spain.
authors.forename: M G
authors.initials: MG
authors.lastname: Barcia
authors.forename: J M
authors.initials: JM
authors.lastname: Castro
authors.forename: C D
authors.initials: CD
authors.lastname: Jullien
authors.forename: M
authors.initials: M
authors.lastname: Freire
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D047388:Casein Kinases; D002478:Cells, Cultured; D005260:Female; D006367:HeLa Cells; D006801:Humans; D008213:Lymphocyte Activation; D008214:Lymphocytes / Q000378:metabolism; D051379:Mice; D008807:Mice, Inbred BALB C; D008969:Molecular Sequence Data; D010766:Phosphorylation; D011494:Protein Kinases / Q000378:metabolism; D011498:Protein Precursors / Q000737:chemistry / Q000378:metabolism*; D013379:Substrate Specificity; D013947:Thymosin / Q000031:analogs & derivatives* / Q000737:chemistry / Q000378:metabolism
chemical_list: D011498:Protein Precursors; C040782:prothymosin alpha; D013947:Thymosin; D011494:Protein Kinases; D047388:Casein Kinases