Initiation of translation and cellular localization of Theileria annulata casein kinase IIalpha: implication for its role in host cell transformation.
Theileria annulata and T. parva are protozoa that infect bovine leukocytes which leads to subsequent transformation and uncontrolled proliferation of these cells. It has been proposed that the CKIIalpha subunit of T. parva induces mitogenic pathways of host leukocytes by being exported into the host cell. The evidence for this is the existence of a predicted N-terminal secretion signal-like peptide. We tested this hypothesis by analyzing gene structure, translation, and protein localization of the T. annulata CKIIalpha (TaCKIIalpha). The determined TaCKIIalpha-ORF potentially codes for a 50 kDa protein with an N-terminal extension including a possible signal sequence not present in CKIIalpha proteins of non-Theileria species. However, antisera raised against TaCKIIalpha recognized a protein of a molecular weight of about 40 kDa and, therefore, inconsistent with this predicted molecular weight. We demonstrate by in vitro transcription/translation that this discrepancy is due to translation from a downstream initiation site omitting the putative N-terminal signal sequence and thus excluding the notion that the protein product is secreted via the classical secretory pathway. In corroboration immunofluorescence investigations suggest that the TaCKIIalpha subunit is confined to the parasite schizonts within the host cell. On the basis of the above findings it seems highly unlikely that export via the classical pathway of the parasite CKIIalpha is the way in which this protein possibly contributes to host cell transformation.
Biermann
Reinhild
R
Division of Veterinary Infectiology and Immunology, Research Center Borstel, Parkallee 22, Borstel, Germany.
Schnittger
Leonhard
L
Beyer
Doreen
D
Ahmed
Jabbar S
JS
D000595:Amino Acid Sequence; D000818:Animals; D047390:Casein Kinase II; D002455:Cell Division; D002460:Cell Line; D002471:Cell Transformation, Neoplastic; D015971:Gene Expression Regulation, Enzymologic; D006790:Host-Parasite Interactions; D007438:Introns / Q000235:genetics; D008969:Molecular Sequence Data; D008970:Molecular Weight; D016366:Open Reading Frames / Q000235:genetics; D014176:Protein Biosynthesis; D017346:Protein Serine-Threonine Kinases / Q000096:biosynthesis* / Q000737:chemistry / Q000378:metabolism*; D021382:Protein Sorting Signals; D021381:Protein Transport; D016415:Sequence Alignment; D013045:Species Specificity; D016796:Theileria annulata / Q000201:enzymology* / Q000235:genetics / Q000254:growth & development / Q000378:metabolism; D014158:Transcription, Genetic
D021382:Protein Sorting Signals; D047390:Casein Kinase II; D017346:Protein Serine-Threonine Kinases