The Leucine-rich Repeat Protein LRIG1 Is a Negative Regulator of ErbB Family Receptor Tyrosine Kinases

Abstract

The molecular mechanisms by which mammalian receptor tyrosine kinases are negatively regulated remain largely unexplored. Previous genetic and biochemical studies indicate that Kekkon-1, a transmembrane protein containing leucine-rich repeats and an immunoglobulin-like domain in its extracellular region, acts as a feedback negative regulator of epidermal growth factor (EGF) receptor signaling in Drosophila melanogaster development. Here we tested whether the related human LRIG1 (also called Lig-1) protein can act as a negative regulator of EGF receptor and its relatives, ErbB2, ErbB3, and ErbB4. We observed that in co-transfected 293T cells, LRIG1 forms a complex with each of the ErbB receptors independent of growth factor binding. We further observed that co-expression of LRIG1 with EGF receptor suppresses cellular receptor levels, shortens receptor half-life, and enhances ligand-stimulated receptor ubiquitination. Finally, we observed that co-expression of LRIG1 suppresses EGF-stimulated transformation of NIH3T3 fibroblasts and that the inducible expression of LRIG1 in PC3 prostate tumor cells suppresses EGF-and neuregulin-1-stimulated cell cycle progression. Our observations indicate that LRIG1 is a negative regulator of the ErbB family of receptor tyrosine kinases and suggest that LRIG1-mediated receptor ubiquitination and degradation may contribute to the suppression of ErbB receptor function.The four members of the ErbB family of receptor tyrosine kinases (epidermal growth factor (EGF) 1 receptor, ErbB2, ErbB3, and ErbB4) play key roles in mediating the development of a variety of tissues, and the aberrant activation of these receptors contributes to the growth and progression of numerous tumor types (1, 2). Binding of EGF-like family ligands to ErbB receptors stimulates receptor dimerization, kinase activation, autophosphorylation, and the engagement of multiple intracellular growth signaling pathways. Although considerable effort over the past two decades has gone into understanding mechanisms by which ErbB receptors are activated and signals are propagated, our understanding of the variety of molecular mechanisms underlying the suppression of growth factor receptor activity remains in its infancy.Growth factor-stimulated receptor down-regulation, involving receptor internalization and the cbl-mediated ubiquitination and trafficking of receptors to lysosomes (3, 4), represents one mechanism for preventing hypersignaling by the ErbB receptors. However, whereas EGF receptor (ErbB1 or EGFR) efficiently couples to cbl following stimulation with its ligand EGF, the ErbB2, ErbB3, and ErbB4 receptors do not efficiently couple to cbl following stimulation with neuregulin-1 (NRG1) (5) and do not undergo efficient NRG1-stimulated down-regulation (6, 7). Hence, other negative regulatory mechanisms may play major roles in suppressing ErbB receptor activity.Studies from the fruit fly Drosophila melanogaster point to the existence of several classes of proteins that negatively regulate EGF receptor activity in flies (...

Biomarkers for Progenitor and Differentiated Epithelial Cells in the Human Meibomian Gland

“…Other studies, though, have reported that Lrig1‐expressing stem cells are predominantly quiescent 8, 25, and that Lrig1 serves as a negative regulator of EGF receptor signaling to suppress stem cell proliferation 8, 27, 28. How, then, do we explain our finding that EGF and BPE promote proliferation, and stimulate the accumulation of Lrig1, in HMGECs?…”

Negative regulation of receptor tyrosine kinases: unexpected links to c-Cbl and receptor ubiquitylation

“…Two negative regulators of RTKs, namely Sprouty and Kekkon, which have subsequently evolved in insects, retain complex relationships with Cbl both in insects and in mammals [23][24][25][26]. In addition, the association of these inhibitors with Cbl leads to the ubiquitylation and degradation of Sprouty and LRIG in the proteasome, which subsequently limits their inhibitory capacity (see Fig.…”

“…The structural similarity of LRIG1 to Kekkons predicted that LRIG1 would interact with and restrict ErbB signaling in mammals. Indeed, LRIG1 localizes to the basolateral surface of epithelial cells, the site of ErbB function, and physically interacts with all members of the ErbB family [23,25]. This recognition involves both LRIG1's and the receptor's ectodomains and it requires no stimulation by the respective ErbB ligand.…”

“…Conclusions derived from both in vivo and in vitro assays suggest that the N-terminal half of c-Cbl directly binds to the juxtamembrane region of LRIG1 [23]. By recruiting c-Cbl to the vicinity of EGFR, both LRIG1 and the receptor undergo ubiquitylation and subsequent degradation [23,25]. Remarkably, Kekkon1-EGFR interaction inhibits EGFR signaling in an apparently different mechanism, which involves inhibition of growth factor binding, receptor auto-phosphorylation and MAPK activation in response to EGF [41].…”

Immunohistochemical analysis of LRIG proteins in meningiomas: correlation between estrogen receptor status and LRIG expression

“…It has been suggested that the subcellular localization of the LRIG proteins may be biologically important [13,14]. LRIG1, located at chromosome 3p14.3 [12], encodes a negative feedback regulator of epidermal growth factor receptor (EGFR) signaling [13] that enhances receptor ubiquitination and degradation rates and inhibits signaling [15][16][17]. EGFR is commonly expressed in meningiomas [18][19][20].…”