title: ERK crosstalks with 4EBP1 to activate cyclin D1 translation during quinol-thioether-induced tuberous sclerosis renal cell carcinoma.
abstract: The mammalian target of rapamycin (mTOR) and mitogen-activated protein kinase signaling cascades have been implicated in a number of human cancers. The tumor suppressor gene tuberous sclerosis-2 (Tsc-2) functions as a negative regulator of mTOR. Critical proteins in both pathways are activated following treatment of Eker rats (Tsc-2(EK/+)) with the nephrocarcinogen 2,3,5-tris-(glutathion-S-yl)hydroquinone (TGHQ), which also results in loss of the wild-type allele of Tsc-2 in renal preneoplastic lesions and tumors. Western blot analysis of kidney tumors formed following treatment of Tsc-2(EK/+) rats with TGHQ for 8 months revealed increases in B-Raf, Raf-1, pERK, cyclin D1, 4EBP1, and p-4EBP1-Ser65, -Thr70, and -Thr37/46 expression. Similar changes are observed following TGHQ-mediated transformation of primary renal epithelial cells derived from Tsc-2(EK/+) rats (quinol-thioether rat renal epithelial [QTRRE] cells) that are also null for tuberin. These cells exhibit high ERK, B-Raf, and Raf-1 kinase activity and increased expression of all p-4EBP1s and cyclin D1. Treatment of the QTRRE cells with the Raf kinase inhibitor, sorafenib, or the MEK1/2 kinase inhibitor, PD 98059, produced a significant decrease in the protein expression of all p-4EBP1s and cyclin D1. Following siRNA knockdown of Raf-1, Western blot analysis revealed a significant decrease in Raf-1, cyclin D1, and all p-4EBP1 forms noted above. In contrast, siRNA knockdown of B-Raf resulted in a nominal change in these proteins. The data indicate that Raf-1/MEK/ERK participates in crosstalk with 4EBP1, which represents a novel pathway interaction leading to increased protein synthesis, cell growth, and kidney tumor formation.
authors.affiliation: Southwest Environmental Health Sciences Center, Department of Pharmacology and Toxicology, College of Pharmacy, The University of Arizona, Tucson, AZ 85721, USA.
authors.forename: Jennifer D
authors.initials: JD
authors.lastname: Cohen
authors.forename: Jaime M C
authors.initials: JM
authors.lastname: Gard
authors.forename: Raymond B
authors.initials: RB
authors.lastname: Nagle
authors.forename: Justin D
authors.initials: JD
authors.lastname: Dietrich
authors.forename: Terrence J
authors.initials: TJ
authors.lastname: Monks
authors.forename: Serrine S
authors.initials: SS
authors.lastname: Lau
mesh_terms: D000818:Animals; D002292:Carcinoma, Renal Cell / Q000139:chemically induced* / Q000235:genetics / Q000378:metabolism / Q000473:pathology; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism*; D018929:Cell Culture Techniques; D002460:Cell Line; D002471:Cell Transformation, Neoplastic / Q000187:drug effects / Q000235:genetics / Q000378:metabolism; D019938:Cyclin D1 / Q000096:biosynthesis* / Q000235:genetics; D004847:Epithelial Cells / Q000187:drug effects / Q000378:metabolism; D048049:Extracellular Signal-Regulated MAP Kinases / Q000235:genetics / Q000378:metabolism*; D015972:Gene Expression Regulation, Neoplastic; D005978:Glutathione / Q000031:analogs & derivatives* / Q000633:toxicity; D006801:Humans; D006873:Hydroquinones / Q000633:toxicity*; D007150:Immunohistochemistry; D047908:Intracellular Signaling Peptides and Proteins; D007680:Kidney Neoplasms / Q000139:chemically induced* / Q000235:genetics / Q000378:metabolism / Q000473:pathology; D019656:Loss of Heterozygosity; D020930:MAP Kinase Kinase Kinases / Q000235:genetics / Q000378:metabolism; D008297:Male; D010750:Phosphoproteins / Q000235:genetics / Q000378:metabolism*; D014176:Protein Biosynthesis; D048493:Proto-Oncogene Proteins B-raf / Q000235:genetics / Q000378:metabolism; D019908:Proto-Oncogene Proteins c-raf; D034741:RNA, Small Interfering / Q000235:genetics; D051381:Rats; D011922:Rats, Mutant Strains; D020239:Receptor Cross-Talk / Q000187:drug effects; D015398:Signal Transduction; D000077005:Tuberous Sclerosis Complex 2 Protein; D025521:Tumor Suppressor Proteins / Q000096:biosynthesis / Q000235:genetics*
chemical_list: D002352:Carrier Proteins; C530106:Ccnd1 protein, rat; C499526:Eif4ebp1 protein, rat; D006873:Hydroquinones; D047908:Intracellular Signaling Peptides and Proteins; D010750:Phosphoproteins; D034741:RNA, Small Interfering; C000624653:TSC2 protein, human; C000624655:Tsc2 protein, rat; D000077005:Tuberous Sclerosis Complex 2 Protein; D025521:Tumor Suppressor Proteins; C078765:2,3,5-(triglutathion-S-yl)hydroquinone; D019938:Cyclin D1; D048493:Proto-Oncogene Proteins B-raf; D019908:Proto-Oncogene Proteins c-raf; C546782:Raf1 protein, rat; D048049:Extracellular Signal-Regulated MAP Kinases; D020930:MAP Kinase Kinase Kinases; D005978:Glutathione