The soluble form of pan-RTK inhibitor and tumor suppressor LRIG1 mediates downregulation of AXL through direct protein–protein interaction in glioblastoma

Abstract

Background Targeted approaches for inhibiting epidermal growth factor receptor (EGFR) and other receptor tyrosine kinases (RTKs) in glioblastoma (GBM) have led to therapeutic resistance and little clinical benefit, raising the need for the development of alternative strategies. Endogenous LRIG1 (Leucine-rich Repeats and ImmunoGlobulin-like domains protein 1) is an RTK inhibitory protein required for stem cell maintenance, and we previously demonstrated the soluble ectodomain of LRIG1 (sLRIG1) to potently inhibit GBM growth in vitro and in vivo. Methods Here, we generated a recombinant protein of the ectodomain of LRIG1 (sLRIG1) and determined its activity in various cellular GBM models including patient-derived stem-like cells and patient organoids. We used proliferation, adhesion, and invasion assays, and performed gene and protein expression studies. Proximity ligation assay and NanoBiT complementation technology were applied to assess protein–protein interactions. Results We show that recombinant sLRIG1 downregulates EGFRvIII but not EGFR, and reduces proliferation in GBM cells, irrespective of their EGFR expression status. We find that sLRIG1 targets and downregulates a wide range of RTKs, including AXL, and alters GBM cell adhesion. Mechanistically, we demonstrate that LRIG1 interferes with AXL but not with EGFR dimerization. Conclusions These results identify AXL as a novel sLRIG1 target and show that LRIG1-mediated RTK downregulation depends on direct protein interaction. The pan-RTK inhibitory activity of sLRIG1 warrants further investigation for new GBM treatment approaches.

LRIG1, a regulator of stem cell quiescence and a pleiotropic feedback tumor suppressor

“…5 ; [ 100 ]) indicate that LRIG1, as a tumor suppressor, may also be therapeutic. In fact, the ECD (ectodomain) of LRIG1 has been reported to display tumor-inhibitory and therapeutic effects in several cancers [ 109 - 111 ]. ECD shedding is the release of the soluble extracellular domain following proteolytic cleavage, an irreversible post-translational modification fundamental in cellular processes and pathologies [ 112 ].…”

LRIG2 promotes glioblastoma progression by modulating innate antitumor immunity through macrophage infiltration and polarization

“… 16–19 Knocking out LRIG2 suppresses glioma formation and progression 20 The extracellular domain of LRIG2 can be cleaved and shed from the cell membrane and secreted into the glioma microenvironment. 21–24 sLRIG2 has similar functions to LRIG2, 22 Therefore, we hypothesized that LRIG2 or sLRIG2 reconfigures the TME to facilitate glioma development.…”

MiR-218-5p promotes breast cancer progression via LRIG1

“…LRIG1, a member of the LRIG family of transmembrane leucine-rich repeat proteins, is a negative regulator of several oncogenic receptor tyrosine kinases, including all members of the ErbB family [12][13][14] as well as the Met [15] and Ret receptors [16] . LRIG1 is broadly expressed in healthy tissue [17] , but its expression decreases in cancers such as renal cell carcinoma [18] , cervical cancer [19] , and breast cancer [14] .…”