title: Role of mammalian target of rapamycin signaling in compensatory renal hypertrophy.
abstract: Loss of functioning nephrons stimulates the growth of residual kidney tissue to augment work capacity and maintain normal renal function. This growth largely occurs by hypertrophy rather than from hyperplasia of the remaining nephrons. The signaling mechanisms that increase RNA and protein synthesis during compensatory renal hypertrophy are unknown. This study found that the remaining kidney hypertrophied 42% by 16 d after unilateral nephrectomy (UNX) in DBA/2 mice. Immunoblotting analysis revealed increased phosphorylation of the 40S ribosomal protein S6 (rpS6) and the eukaryotic translation initiation factor (eIF) 4E-binding protein 1 (4E-BP1), the two downstream effectors of the mammalian target of rapamycin (mTOR). The highly specific mTOR inhibitor rapamycin blocked UNX-increased phosphorylation of both rpS6 and 4E-BP1. UNX increased the content of not only 40S and 60S ribosomal subunits but also 80S monosomes and polysomes in the remaining kidney. Administration of rapamycin decreased UNX-induced polysome formation and shifted the polysome profile in the direction of monosomes and ribosomal subunits. Pretreatment of the mice with rapamycin inhibited UNX-induced hypertrophy. These studies demonstrate that activation of the mTOR signaling pathway in the remaining kidney after UNX plays an essential role in modulating RNA and protein synthesis during development of compensatory renal hypertrophy.
authors.affiliation: Division of Nephrology, Department of Medicine, Vanderbilt University School of Medicine, S 3223 Medical Center North, Nashville, Tennessee 37232, USA. jiankang.chen@vanderbilt.edu
authors.forename: Jian-Kang
authors.initials: JK
authors.lastname: Chen
authors.forename: Jianchun
authors.initials: J
authors.lastname: Chen
authors.forename: Eric G
authors.initials: EG
authors.lastname: Neilson
authors.forename: Raymond C
authors.initials: RC
authors.lastname: Harris
mesh_terms: D000222:Adaptation, Physiological / Q000502:physiology*; D048868:Adaptor Proteins, Signal Transducing; D000818:Animals; D002352:Carrier Proteins / Q000378:metabolism; D018797:Cell Cycle Proteins; D039642:Eukaryotic Initiation Factors; D006984:Hypertrophy; D007166:Immunosuppressive Agents / Q000494:pharmacology; D007668:Kidney / Q000473:pathology / Q000502:physiology*; D008297:Male; D051379:Mice; D008811:Mice, Inbred DBA; D009392:Nephrectomy; D010750:Phosphoproteins / Q000378:metabolism; D010766:Phosphorylation / Q000187:drug effects; D011132:Polyribosomes / Q000502:physiology; D011494:Protein Kinases / Q000378:metabolism*; D015398:Signal Transduction / Q000502:physiology*; D020123:Sirolimus / Q000494:pharmacology; D058570:TOR Serine-Threonine Kinases
chemical_list: D048868:Adaptor Proteins, Signal Transducing; D002352:Carrier Proteins; D018797:Cell Cycle Proteins; C499527:Eif4ebp1 protein, mouse; D039642:Eukaryotic Initiation Factors; D007166:Immunosuppressive Agents; D010750:Phosphoproteins; D011494:Protein Kinases; C546843:mTOR protein, mouse; D058570:TOR Serine-Threonine Kinases; D020123:Sirolimus