title: The 5' untranslated region of protein kinase Cdelta directs translation by an internal ribosome entry segment that is most active in densely growing cells and during apoptosis.
abstract: Protein kinase Cdelta (PKCdelta) is a member of the PKC family of phospholipid-dependent serine/threonine kinases and is involved in cell proliferation, apoptosis, and differentiation. Previous studies have suggested that different PKC isoforms might be translationally regulated. We report here that the 395-nt-long 5' untranslated region (5' UTR) of PKCdelta is predicted to form very stable secondary structures with free energies (deltaG values) of around -170 kcal/mol. The 5' UTR of PKCdelta can significantly repress luciferase translation in rabbit reticulocyte lysate but does not repress luciferase translation in a number of transiently transfected cell lines. By using a bicistronic luciferase reporter, we show that the 5' UTR of PKCdelta contains a functional internal ribosome entry segment (IRES). The activity of the PKCdelta IRES is greatest in densely growing cells and during apoptosis, when total protein synthesis and levels of full-length eukaryotic initiation factor 4G are reduced. However, the IRES activity of the 5' UTR of PKCdelta is not enhanced during serum starvation, another condition shown to inhibit cap-dependent translation, suggesting that its potency is dependent on specific cellular conditions. Accumulating data suggest that PKCdelta has a function as proliferating cells reach high density and in early and later events of apoptosis. Our studies suggest a mechanism whereby PKCdelta synthesis can be maintained under these conditions when cap-dependent translation is inhibited.
authors.affiliation: Department of Biology, University of York, York YO10 5YW, United Kingdom. morrishb@cryptic.rch.unimelb.edu.au
authors.forename: Bronwyn C
authors.initials: BC
authors.lastname: Morrish
authors.forename: Martin G
authors.initials: MG
authors.lastname: Rumsby
mesh_terms: D016475:3T3 Cells; D020121:5' Untranslated Regions / Q000737:chemistry / Q000235:genetics / Q000502:physiology*; D000818:Animals; D017209:Apoptosis / Q000502:physiology*; D002455:Cell Division / Q000502:physiology*; D002474:Cell-Free System; D004247:DNA / Q000737:chemistry / Q000235:genetics; D005260:Female; D017930:Genes, Reporter; D006367:HeLa Cells; D006801:Humans; D007527:Isoenzymes / Q000235:genetics*; D008156:Luciferases / Q000096:biosynthesis / Q000235:genetics; D051379:Mice; D009690:Nucleic Acid Conformation; D014176:Protein Biosynthesis / Q000502:physiology*; D020033:Protein Isoforms / Q000235:genetics*; D011493:Protein Kinase C / Q000235:genetics*; D051745:Protein Kinase C-delta; D012315:RNA Caps; D011817:Rabbits; D051381:Rats; D011993:Recombinant Fusion Proteins / Q000096:biosynthesis / Q000235:genetics; D012045:Regulatory Sequences, Nucleic Acid; D012270:Ribosomes / Q000378:metabolism* / Q000648:ultrastructure; D014407:Tumor Cells, Cultured
chemical_list: D020121:5' Untranslated Regions; D007527:Isoenzymes; D020033:Protein Isoforms; D012315:RNA Caps; D011993:Recombinant Fusion Proteins; D004247:DNA; D008156:Luciferases; C497259:Prkcd protein, mouse; C497260:Prkcd protein, rat; C497258:PRKCD protein, human; D011493:Protein Kinase C; D051745:Protein Kinase C-delta