Differential role of TNF receptors in cellular trafficking of intact TNF.
OBJECTIVE
Although ligand signaling and degradation within the cell have received much attention, few studies have quantified the role of receptors on the transcytosis of ligand into and out of the cell in intact form. Accordingly, we determined the differential role of the two receptors for tumor necrosis factor alpha (TNFR1, TNFR2) on cellular transcytosis.


METHODS
TNFR1 and TNFR2 were overexpressed in HEK293 cells by transient transfection. Cell surface binding, endocytosis, and exocytosis of (125)I-TNF were quantified. Degradation was determined by acid precipitation and size-exclusion chromatography.


RESULTS
TNFR1- mediated uptake of TNF was faster than TNFR2-mediated uptake of TNF. TNFR2, however, exhibited greater capacity, leading to a higher percentage release of TNF into the exocytosis medium. Rather than being degraded, most of the TNF inside the cell remained intact for 1 h. Both receptors exerted protective roles against degradation, but there was no cooperativity between them.


CONCLUSIONS
The effects of TNFR1 and TNFR2 in shepherding TNF across the cell illustrate the differential roles of receptors on the cellular trafficking of the ligand in intact form so as to facilitate its biological effects.
Pan
Weihong
W
Pennington Biomedical Research Center, Baton Rouge, LA 70808, USA. weihong.pan@pbrc.edu
Tu
Hong
H
Yu
Chuanhui
C
Hsuchou
Hung
H
Yang
Yijun
Y
Kastin
Abba J
AJ
D000818:Animals; D001921:Brain / Q000098:blood supply / Q000378:metabolism; D002460:Cell Line; D004705:Endocytosis; D005786:Gene Expression Regulation; D006801:Humans; D051379:Mice; D008833:Microcirculation / Q000378:metabolism; D011485:Protein Binding; D021381:Protein Transport; D047888:Receptors, Tumor Necrosis Factor, Type I / Q000235:genetics / Q000378:metabolism*; D047889:Receptors, Tumor Necrosis Factor, Type II / Q000235:genetics / Q000378:metabolism*; D048069:Tumor Necrosis Factors / Q000378:metabolism*
D047888:Receptors, Tumor Necrosis Factor, Type I; D047889:Receptors, Tumor Necrosis Factor, Type II; D048069:Tumor Necrosis Factors