Phosphatidylinositol 3-kinase activity is required for epidermal growth factor to suppress proteolysis.
Suppression of protein breakdown occurs commonly in cell growth, but the pathways responsible for controlling proteolysis are poorly understood. Protein breakdown in NRK-52E renal epithelial cells treated with epidermal growth factor (EGF) and intracellular signaling inhibitors or dominant negative signaling molecules contained in an adenoviral vector were measured. The tyrosine kinase inhibitor, herbimycin A, eliminated the suppression of proteolysis induced by EGF. In contrast, the Src inhibitor, PP1, had no effect. Expression of dominant negative H-RasY57 blocked the ability of EGF to stimulate downstream targets of Ras and also reduced the ability of EGF to suppress proteolysis. Inhibiting MEK did not influence the ability of EGF to suppress proteolysis, but the phosphatidylinositol 3-kinase (PI 3-kinase) inhibitor, LY249002, stimulated basal proteolysis and completely eliminated the proteolytic response to EGF. Use of an adenovirus that expresses a dominant negative p85 subunit of class 1 PI 3-kinase completely blocked the ability of EGF to suppress proteolysis, whereas use of an adenovirus expressing a K227E constitutively active p110 subunit reproduced the reduction in protein breakdown. It was concluded that EGF suppresses proteolysis by a mechanism that involves Ras and class 1 PI 3-kinase.
Franch
Harold A
HA
*Renal Division, Department of Medicine, Emory University School of Medicine, Atlanta, Georgia; and †Atlanta Veterans Affairs Medical Center, Decatur, Georgia.
Wang
Xiaonan
X
*Renal Division, Department of Medicine, Emory University School of Medicine, Atlanta, Georgia; and †Atlanta Veterans Affairs Medical Center, Decatur, Georgia.
Sooparb
Sira
S
*Renal Division, Department of Medicine, Emory University School of Medicine, Atlanta, Georgia; and †Atlanta Veterans Affairs Medical Center, Decatur, Georgia.
Brown
Nikia S
NS
*Renal Division, Department of Medicine, Emory University School of Medicine, Atlanta, Georgia; and †Atlanta Veterans Affairs Medical Center, Decatur, Georgia.
Du
Jie
J
*Renal Division, Department of Medicine, Emory University School of Medicine, Atlanta, Georgia; and †Atlanta Veterans Affairs Medical Center, Decatur, Georgia.
D000818:Animals; D016227:Benzoquinones; D002460:Cell Line; D004791:Enzyme Inhibitors / Q000494:pharmacology; D004815:Epidermal Growth Factor / Q000494:pharmacology*; D007684:Kidney Tubules / Q000166:cytology / Q000187:drug effects / Q000201:enzymology* / Q000378:metabolism*; D018374:LLC-PK1 Cells; D047029:Lactams, Macrocyclic; D020928:Mitogen-Activated Protein Kinases / Q000502:physiology; D010447:Peptide Hydrolases / Q000187:drug effects*; D019869:Phosphatidylinositol 3-Kinases / Q000502:physiology*; D011505:Protein-Tyrosine Kinases / Q000037:antagonists & inhibitors; D011809:Quinones / Q000494:pharmacology; D051381:Rats; D017828:Rifabutin / Q000031:analogs & derivatives; D013552:Swine; D018631:ras Proteins / Q000502:physiology
D016227:Benzoquinones; D004791:Enzyme Inhibitors; D047029:Lactams, Macrocyclic; D011809:Quinones; D017828:Rifabutin; D004815:Epidermal Growth Factor; C020754:herbimycin; D019869:Phosphatidylinositol 3-Kinases; D011505:Protein-Tyrosine Kinases; D020928:Mitogen-Activated Protein Kinases; D010447:Peptide Hydrolases; D018631:ras Proteins