title: Diacylglycerol kinase delta and protein kinase C(alpha) modulate epidermal growth factor receptor abundance and degradation through ubiquitin-specific protease 8.
abstract: Many human epithelial cancers are characterized by abnormal activation of the epidermal growth factor receptor (EGFR), which is often caused by its excessive expression in tumor cells. The abundance of EGFR is modulated, in part, by its ubiquitination, which targets it for degradation. The components responsible for adding ubiquitin to EGFR are well characterized, but this is a reversible process, and the mechanisms that modulate the removal of ubiquitin from the EGFR are not well known. We found that de-ubiquitination of EGFR was regulated by diacylglycerol kinase delta (DGKdelta), a lipid kinase that terminates diacylglycerol signaling. In DGKdelta-deficient cells, ubiquitination of EGFR was enhanced, which attenuated the steady-state levels of EGFR and promoted its ligand-induced degradation. These effects were not caused by changes in the ubiquitinating apparatus, but instead were due to reduced expression of the de-ubiquitinase, ubiquitin-specific protease 8 (USP8). Depletion of protein kinase Calpha (PKCalpha), a target of diacylglycerol, rescued the levels of USP8 and normalized EGFR degradation in DGKdelta-deficient cells. Moreover, the effects of PKCalpha were caused by its inhibition of Akt, which stabilizes USP8. Our data indicate a novel mechanism where DGKdelta and PKCalpha modulate the levels of ubiquitinated EGFR through Akt and USP8.
authors.affiliation: Huntsman Cancer Institute, Department of Oncological Sciences, University of Utah, Salt Lake City, Utah 84112, USA.
authors.forename: Jinjin
authors.initials: J
authors.lastname: Cai
authors.forename: Tracy M
authors.initials: TM
authors.lastname: Crotty
authors.forename: Ethan
authors.initials: E
authors.lastname: Reichert
authors.forename: Kermit L
authors.initials: KL
authors.lastname: Carraway
authors.forename: Diana M
authors.initials: DM
authors.lastname: Stafforini
authors.forename: Matthew K
authors.initials: MK
authors.lastname: Topham
mesh_terms: D000818:Animals; D045744:Cell Line, Tumor; D019852:Diacylglycerol Kinase / Q000235:genetics / Q000378:metabolism*; D004705:Endocytosis / Q000502:physiology; D010450:Endopeptidases / Q000235:genetics / Q000378:metabolism*; D056827:Endosomal Sorting Complexes Required for Transport / Q000235:genetics / Q000378:metabolism*; D004789:Enzyme Activation; D066246:ErbB Receptors / Q000235:genetics / Q000378:metabolism*; D006367:HeLa Cells; D006801:Humans; D047908:Intracellular Signaling Peptides and Proteins / Q000235:genetics / Q000378:metabolism; D008175:Lung Neoplasms / Q000378:metabolism; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism; D051379:Mice; D000076250:Myristoylated Alanine-Rich C Kinase Substrate; D051571:Protein Kinase C-alpha / Q000235:genetics / Q000378:metabolism*; D051057:Proto-Oncogene Proteins c-akt / Q000235:genetics / Q000378:metabolism; D050721:Proto-Oncogene Proteins c-cbl / Q000235:genetics / Q000378:metabolism; D034622:RNA Interference; D043222:Ubiquitin Thiolesterase / Q000235:genetics / Q000378:metabolism*; D057149:Ubiquitinated Proteins / Q000235:genetics / Q000378:metabolism; D054875:Ubiquitination
chemical_list: D056827:Endosomal Sorting Complexes Required for Transport; D047908:Intracellular Signaling Peptides and Proteins; D008565:Membrane Proteins; D057149:Ubiquitinated Proteins; D000076250:Myristoylated Alanine-Rich C Kinase Substrate; D050721:Proto-Oncogene Proteins c-cbl; C497139:DGKD protein, human; D019852:Diacylglycerol Kinase; D066246:ErbB Receptors; D051057:Proto-Oncogene Proteins c-akt; D051571:Protein Kinase C-alpha; D010450:Endopeptidases; D043222:Ubiquitin Thiolesterase; C541536:Usp8 protein, mouse