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.
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.
Morrish
Bronwyn C
BC
Department of Biology, University of York, York YO10 5YW, United Kingdom. morrishb@cryptic.rch.unimelb.edu.au
Rumsby
Martin G
MG
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
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