HIV-1 viral protein r induces ERK and caspase-8-dependent apoptosis in renal tubular epithelial cells.
OBJECTIVE
HIV-associated nephropathy (HIVAN) is the most common cause of end-stage renal disease in persons with HIV/AIDS and is characterized by focal glomerulosclerosis and dysregulated renal tubular epithelial cell (RTEC) proliferation and apoptosis. HIV-1 viral protein r (Vpr) has been implicated in HIV-induced RTEC apoptosis but the mechanisms of Vpr-induced RTEC apoptosis are unknown. The aim of this study was therefore to determine the mechanisms of Vpr-induced apoptosis in RTEC.


METHODS
Apoptosis and caspase activation were analyzed in human RTEC (HK2) after transduction with Vpr-expressing and control lentiviral vectors. Bax and BID were inhibited with lentiviral shRNA, and ERK activation was blocked with the MEK1,2 inhibitor, U0126.


RESULTS
Vpr induced apoptosis as indicated by caspase 3/7 activation, PARP-1 cleavage and mitochondrial injury. Vpr activated both caspases-8 and 9. Inhibition of Bax reduced Vpr-induced apoptosis, as reported in other cell types. Additionally, Vpr-induced cleavage of BID to tBID and suppression of BID expression prevented Vpr-induced apoptosis. Since sustained ERK activation can activate caspase-8 in some cell types, we studied the role of ERK in Vpr-induced caspase-8 activation. Vpr induced sustained ERK activation in HK2 cells and incubation with U0126 reduced Vpr-induced caspase-8 activation, BID cleavage and apoptosis. We detected phosphorylated ERK in RTEC in HIVAN biopsy specimens by immunohistochemistry.


CONCLUSIONS
These studies delineate a novel pathway of Vpr-induced apoptosis in RTEC, which is mediated by sustained ERK activation, resulting in caspase 8-mediated cleavage of BID to tBID, thereby facilitating Bax-mediated mitochondrial injury and apoptosis.
Snyder
Alexandra
A
Department of Nephrology, Mount Sinai School of Medicine, New York, New York 10029, USA.
Alsauskas
Zygimantas C
ZC
Leventhal
Jeremy S
JS
Rosenstiel
Paul E
PE
Gong
Pengfei
P
Chan
Justin J K
JJ
Barley
Kevin
K
He
John C
JC
Klotman
Mary E
ME
Ross
Michael J
MJ
Klotman
Paul E
PE
D016263:AIDS-Associated Nephropathy / Q000235:genetics / Q000378:metabolism* / Q000821:virology; D017209:Apoptosis / Q000235:genetics / Q000502:physiology*; D053181:Caspase 8 / Q000235:genetics / Q000378:metabolism*; D049109:Cell Proliferation; D048049:Extracellular Signal-Regulated MAP Kinases / Q000378:metabolism*; D015967:Gene Expression Regulation, Viral; D016336:Gene Products, vpr / Q000235:genetics / Q000378:metabolism*; D015497:HIV-1; D006801:Humans; D007676:Kidney Failure, Chronic / Q000235:genetics / Q000378:metabolism* / Q000821:virology; D007684:Kidney Tubules / Q000821:virology; D012367:RNA, Viral; D014779:Virus Replication
D016336:Gene Products, vpr; D012367:RNA, Viral; D048049:Extracellular Signal-Regulated MAP Kinases; D053181:Caspase 8
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