Stimulation of Leukemia Inhibitory Factor Receptor Degradation by Extracellular Signal-regulated Kinase

Abstract

Leukemia inhibitory factor (LIF) signals via the heterodimeric receptor complex comprising the LIF receptor ␣ subunit (LIFR␣) and the common signal transducing subunit for interleukin-6 cytokine receptors, gp130. This study demonstrates that in different cell types, the level of LIFR␣ decreases during treatment with LIF or the closely related cytokine oncostatin M (OSM). Moreover, insulin and epidermal growth factor induce a similar LIFR␣ down-regulation. The regulated loss of LIFR␣ is specific since neither gp130 nor OSM receptor ␤ shows a comparable change in turnover. LIFR␣ downregulation correlates with reduced cell responsiveness to LIF. Using protein kinase inhibitors and point mutations in LIFR␣, we demonstrate that LIFR␣ downregulation depends on activation of extracellular signalregulated kinase 1/2 and phosphorylation of the cytoplasmic domain of LIFR␣ at serine 185. This modification appears to promote the endosomal/lysosomal pathway of the LIFR␣. These results suggest that extracellular signal-regulated kinase-activating factors like OSM and growth factors have the potential to lower specifically LIF responsiveness in vivo by regulating LIFR␣ half-life. Leukemia inhibitory factor (LIF)1 is one member of the interleukin (IL)-6-type family of cytokines that also include IL-6, IL-11, oncostatin M (OSM), ciliary neurotrophic factor (CNTF), cardiotrophin-1 (CT-1), and neurotrophin-1. LIF is a pleiotropic cytokine that, among other functions, induces differentiation of mouse monocytic leukemia M1 cells, conversion of sympathetic neurons from the adrenergic to cholinergic phenotype, suppresses the differentiation of embryonic stem cells, enhances proliferation of myoblasts, and facilitates endometrial implantation of embryos (reviewed in Refs. 1 and 2).LIF also plays a role in the systemic inflammatory response, activating the hypothalamic-adrenal axis, and inducing the acute phase reaction of the liver (3). In hepatocytes, LIF, similar to other IL-6 cytokines, stimulates the enhanced expression of a set of plasma proteins, termed acute phase proteins (APP) (4). The precise pattern of APP expression is determined by the action of IL-6 cytokines in combination with various other inflammatory mediators, endocrine hormones, and growth factors (5). For instance, during the acute phase reaction, insulin is increased 3-fold (6) and then modulates the cytokine regulation of APP genes (7,8). In myoblasts, IGF-1 also reduces LIF action, apparently by down-regulating LIF receptor number (9).LIFR␣ is a 190-kDa transmembrane protein with low affinity for LIF. In combination with gp130 subunit, it forms the high affinity LIF receptor complex (10, 11). As described in the human system, OSM also uses LIFR␣ and gp130 subunits to form a high affinity OSM receptor complex (then termed OSMR complex type I). CNTF, CT-1, and neurotrophin-1 also utilize LIFR␣ and gp130 subunits (reviewed in Refs. 12 and 13). In addition to the shared LIFR␣/gp130 complex used by either LIF or OSM, a specific OSM receptor complex (type II) has bee...

FR901228, an inhibitor of histone deacetylases, increases the cellular responsiveness to IL-6 type cytokines by enhancing the expression of receptor proteins

“…The immediate activation of the JAK-STAT and ERK pathways by short-term treatment with IL-6 cytokines has been used to identify the presence and relative activity of specific receptor systems in various cell types (Gadient and Patterson, 1999;Klausen et al, 2000;Douglas et al, 1997;Blanchard et al, 2000;Wang et al, 2000). Based on the cytokine-stimulated phosphorylation of STAT3, we determined that normal adult mouse hepatocytes respond equally to LIF, OSM and IL-6 (Figure 1a).…”

“…This preference, which is detectable in many cell types, is attributed to the specific signaling capabilities of the OSMR complex (Klausen et al, 2000;Blanchard et al, 2000;Wang et al, 2000). To obtain a reference for the maximal activation of the ERK pathway independent of IL-6 cytokine receptor signals, hepatocytes, fibroblasts and epithelial cells were treated with EGF and macrophages with lipopolysaccharides (LPS) (Figure 1a,b).…”

“…Every cell type in the adult organism expresses at least one of the receptors for IL-6 cytokines. However, the precise composition of active receptors that is expressed in a given cell type is determined firstly by the developmental differentiation program of the particular tissue cell and secondly by regulatory processes associated with a given receptor subunit (e.g., turnover; Blanchard et al, 2000). However, the cell-specific pattern of receptor expression is often subject to profound alterations during malignant transformation.…”

Oncostatin M Regulates the Synthesis and Turnover of gp130, Leukemia Inhibitory Factor Receptor α, and Oncostatin M Receptor β by Distinct Mechanisms

“…Containment of IL-6 cytokine signaling appears to be directed by two distinct mechanisms, (a) the induction or mobilization of factors that attenuate functions of the cytoplasmic domains of the receptor proteins and (b) the enhanced degradation of receptor proteins. Recently we have also demonstrated that receptor signals acting in trans determine the level of the receptor subunit LIFR␣ and, thus, the cellular responsiveness to LIF (12). ERK 1/2, activated by IL-6 cytokines or growth factors, phosphorylates serine 1044 (or serine 185 of the cytoplasmic domain) of LIFR␣, leading to its lysosomal degradation independent of LIF binding (12,13).…”

“…Recently we have also demonstrated that receptor signals acting in trans determine the level of the receptor subunit LIFR␣ and, thus, the cellular responsiveness to LIF (12). ERK 1/2, activated by IL-6 cytokines or growth factors, phosphorylates serine 1044 (or serine 185 of the cytoplasmic domain) of LIFR␣, leading to its lysosomal degradation independent of LIF binding (12,13). An additional ERK-independent degradation pathway for LIFR␣ has also been observed in NIH-3T3 cells, but this degradation occurred only after LIF treatment (12).…”