Shedding of interleukin‐6 receptor and tumor necrosis factor α

Abstract

A functionally and structurally diverse group of transmembrane proteins including transmembrane forms of mediators or receptors can be proteolytically cleaved to form soluble growth factors or receptors. Recently, the proteolytic activity responsible for pro-tumor necrosis factor a (proTNFa) processing has been identified and named TACE (TNFa converting enzyme). In experiments with TACE deficient (TACE -/-) fibroblasts we found that 4b-phorbol 12-myristate 13-acetate (PMA)-induced shedding of the interleukin-6 receptor (IL-6R) is strongly reduced. A basal hydroxamate sensitive release of IL-6R, however, could still be detected. This result demonstrates that TACE plays a role in IL-6R processing and that additional metalloproteases might be involved. PMA-induced shedding of IL-6R in TACE deficient mouse fibroblasts could be restored by stable transfection of a TACE cDNA. To characterize differences between shedding of IL-6R and proTNFa we generated chimeric IL-6R and proTNFa proteins wherein the endogenous cleavage sites (CS) had been replaced by the corresponding region of proTNFa and IL-6R, respectively. Interestingly, proTNFa chimeric proteins showed only minimal shedding. In contrast, IL-6R chimeras containing the proTNFa CS were shed spontaneously, processing was not further induced by PMA. Thus, the cleavage pattern transferred by the introduction of the proTNFa CS is similar to that of proTNFa itself. We conclude that the amino-acid sequence at the proteolytic CS contributes to the cleavage characteristics of a protein. However, this information alone is not sufficient to transfer cleavability as seen with proTNFa chimeras containing the IL-6R CS and which were resistant to shedding.

Soluble Axl Is Generated by ADAM10-Dependent Cleavage and Associates with Gas6 in Mouse Serum

“…Ras-Myc-retrovirusimmortalized TACE Ϫ/Ϫ (generously provided by S. Rose-John, Christian-Albrechts-University, Kiel, Germany), simian virus large T antigen (SV-T)-immortalized ADAM10 Ϫ/Ϫ , primary Axl Ϫ/Ϫ mouse embryo fibroblasts (MEFs), and respective wild-type (WT) cells were generated and characterized as described elsewhere (3,36,53). Axl Ϫ/Ϫ MEFs were immortalized by stable transfection with the simian virus 40 large T antigen expression vector pMSSVLT (58).…”

Growth Hormone (GH)-induced Dimerization Inhibits Phorbol Ester-stimulated GH Receptor Proteolysis

“…Thus, neither the full cytoplasmic domain nor any particular cytoplasmic domain region (at least distal to the Box 1 element) is clearly required for PMA-induced receptor proteolysis. We do not yet know if the increased remnant present in CHO-rbGHR del 297-406 cells even in the absence of PMA reflects an alteration in basal protease sensitivity in this mutant; such a change in protease specificity has been noted, for example, in mutants of the interleukin 6 receptor, another TACE substrate (53). In any case, the parallel findings of PMA-inducible proteolysis in the wild-type and mutant rbGHRs indicate the utility of both stably transfected CHO cell lines as model systems in the current study.…”

Shedding of the Transferrin Receptor Is Mediated Constitutively by an Integral Membrane Metalloprotease Sensitive to Tumor Necrosis Factor α Protease Inhibitor-2

“…The stimulation of PKC by treating cells with PMA leads to a reduction of cell surface expression of L-selectin and p75 TNF receptor only from wild-type cells but not TACE inactive cells (30). The PMA-induced shedding of interleukin-6 receptor is also strongly reduced in TACE-deficient fibroblasts, whereas a basal release could still be detected (41). In addition disruption of the TACE gene also abolishes regulated ␣-cleavage of APP in cultured cells, whereas the basal secretion of soluble APP is unaffected in cells derived from TACE knockout mice (42).…”