Proteasome regulation of ULBP1 transcription.
Killer lymphocytes recognize stress-activated NKG2D ligands on tumors. We examined NKG2D ligand expression in head and neck squamous cell carcinoma (HNSCC) cells and other cell lines. HNSCC cells typically expressed MHC class I chain-related gene A (MICA), MICB, UL16-binding protein (ULBP)2, and ULBP3, but they were uniformly negative for cell surface ULBP1 and ULBP4. We then studied how cancer treatments affected NKG2D ligand expression. NKG2D ligand expression was not changed by most cancer-relevant treatments. However, bortezomib and other proteasome inhibitor drugs with distinct mechanisms of action dramatically and specifically up-regulated HNSCC ULBP1 mRNA and cell surface protein. Proteasome inhibition also increased RNA for ULBP1 and other NKG2D ligands in nontransformed human keratinocytes. Proteasome inhibitor drugs increased ULBP1 transcription by acting at a site in the 522-bp ULBP1 promoter. Although the DNA damage response pathways mediated by ATM (ataxia-telangiectasia, mutated) and ATR (ATM and Rad3-related) signaling had been reported to up-regulate NKG2D ligand expression, we found that ULBP1 up-regulation was not inhibited by caffeine and wortmannin, inhibitors of ATM/ATR signaling. ULBP1 expression in HNSCC cells was not increased by several ATM/ATR activating treatments, including bleomycin, cisplatin, aphidicolin, and hydroxyurea. Ionizing radiation caused ATM activation in HNSCC cells, but high-level ULBP1 expression was not induced by gamma radiation or UV radiation. Thus, ATM/ATR signaling was neither necessary nor sufficient for high-level ULBP1 expression in human HNSCC cell lines and could not account for the proteasome effect. The selective induction of ULBP1 expression by proteasome inhibitor drugs, along with variable NKG2D ligand expression by human tumor cells, indicates that NKG2D ligand genes are independently regulated.
Department of Pathology and Laboratory Medicine, University of Kentucky, Lexington, KY 40536, USA.
James E
JE
Butler
Mikel B
MB
Moore
Steven R
SR
Presnell
Huei-Wei
HW
Chan
N Jan
NJ
Chalupny
Charles T
CT
Lutz
D000970:Antineoplastic Agents / Q000494:pharmacology; D064007:Ataxia Telangiectasia Mutated Proteins; D015153:Blotting, Western; D002294:Carcinoma, Squamous Cell / Q000235:genetics* / Q000378:metabolism; D018797:Cell Cycle Proteins / Q000378:metabolism; D045744:Cell Line, Tumor; D005434:Flow Cytometry; D058851:GPI-Linked Proteins; D005786:Gene Expression Regulation / Q000187:drug effects / Q000502:physiology*; D006258:Head and Neck Neoplasms / Q000235:genetics* / Q000378:metabolism; D006801:Humans; D047908:Intracellular Signaling Peptides and Proteins / Q000235:genetics*; D008565:Membrane Proteins / Q000235:genetics*; D055655:NK Cell Lectin-Like Receptor Subfamily K / Q000378:metabolism; D016133:Polymerase Chain Reaction; D011401:Promoter Regions, Genetic; D046988:Proteasome Endopeptidase Complex / Q000187:drug effects / Q000378:metabolism*; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D015398:Signal Transduction / Q000502:physiology; D014158:Transcription, Genetic / Q000187:drug effects
D000970:Antineoplastic Agents; D018797:Cell Cycle Proteins; D058851:GPI-Linked Proteins; D047908:Intracellular Signaling Peptides and Proteins; C527085:KLRK1 protein, human; D008565:Membrane Proteins; D055655:NK Cell Lectin-Like Receptor Subfamily K; C423231:ULBP1 protein, human; C576597:ATR protein, human; D064007:Ataxia Telangiectasia Mutated Proteins; D017346:Protein Serine-Threonine Kinases; D046988:Proteasome Endopeptidase Complex