LRIG1 regulates cadherin-dependent contact inhibition directing epithelial homeostasis and pre-invasive squamous cell carcinoma development

Dysregulation and antimetastatic function of circLRIG1 modulated by miR-214-3p/LRIG1 axis in bladder carcinoma

CircLRIG1, a newly discovered circRNA, has yet to have its potential function and biological processes reported. This study explored the role of circLRIG1 in the development and progression of bladder carcinoma and its potential molecular mechanisms. Techniques such as qRT-PCR, Western blot, various cellular assays, and in vivo models were used to investigate mRNA and protein levels, cell behavior, molecular interactions, and tumor growth. The results showed that both circLRIG1 and LRIG1 were significantly reduced in bladder carcinoma tissues and cell lines. Low circLRIG1 expression was associated with poor patient prognosis. Overexpressing circLRIG1 inhibited bladder carcinoma cell growth, migration, and invasion, promoted apoptosis, and decreased tumor growth and metastasis in vivo. Importantly, circLRIG1 was found to sponge miR-214-3p, enhancing LRIG1 expression, and its overexpression also modulated protein levels of E-cadherin, N-cadherin, Vimentin, and LRIG1. Similar effects were observed with LRIG1 overexpression. Notably, a positive correlation was found between circLRIG1 and LRIG1 expression in bladder carcinoma tissues. Additionally, the tumor-suppressing effect of circLRIG1 was reversed by overexpressing miR-214-3p or silencing LRIG1. The study concludes that circLRIG1 suppresses bladder carcinoma progression by enhancing LRIG1 expression via sponging miR-214-3p, providing a potential strategy for early diagnosis and treatment of bladder carcinoma.

Leucine-rich repeats and immunoglobulin-like domains protein 1 (LRIG1) is downregulated in Invasive ductal carcinoma and potential prognostic marker of breast cancer

BACKGROUND

LRIG1 belongs to the family of transmembrane proteins containing leucine-rich repeats. LRIGs are considered as tumor suppressors as they negatively regulate receptor tyrosine kinases. The role of LRIG1 as an EGFR regulator makes it an important marker to be studied in various epithelial-derived cancers.

METHODS

LRIG1 expression was determined in Erbb2 + cell lines by western blotting, and cell motility was examined by cell migration assay. The AKT/GSK3-β/β-catenin pathway was determined in the presence of LRIG1 and Erbb2 by using western blotting.

RESULTS

So far, no study has reported the expression of LRIG1 in benign forms of tumor such as fibroadenoma. The current study aims to analyze LRIG1 expression in fibroadenoma and invasive ductal carcinoma (IDC) tissues. In this study, we compared the LRIG1 expression with different clinicopathological parameters of patients having IDC or fibroadenoma. LRIG1 expression was low in Erbb2+ cell lines, and more cell motility was observed. The AKT/GSK3-β/β-catenin pathway was activated when LRIG1 was downregulated; consequently, Erbb2 was upregulated. Our results indicated that LRIG1 expression can be significantly correlated with age, Nottingham index, and Her2/neu status of cancer. The expression of LRIG1 in IDC and fibroadenoma were found to be significantly different.

CONCLUSION

The fibroadenoma tissue sections were found to express LRIG1 more intensely as compared to the IDC sections, which are in line with the studies reporting reduced copy number of the gene either due to gene deletion or transcriptional inhibition. This further supports that the downregulation of LRIG1 may lead to malignant tumor acting as a tumor suppressor.

LRIG1 Levels in Chronic Rhinosinusitis With Nasal Polyps

Purpose: Nasal polyps (NPs), usually occurring together with chronic rhinosinusitis (CRS), are benign masses of mucosal origin arising from inflammation. The transmembrane protein known as leucine-rich repeats and immunoglobulin-like domains 1 (Lrig1) is a member of the Lrig family. Lrig1 is frequently expressed in the respiratory tract and epithelial tissues and can inhibit several signaling pathways involved in cell proliferation. The aim of this study was to determine Lrig1 levels in NP tissues of patients with CRS. Material and Methods: This study included 36 patients with CRS and NPs and 15 patients who underwent rhinoplasty as the control group. The Lrig1 levels of all participants were measured by the ELISA method. Results: This study revealed that Lrig1 levels were significantly lower in NP tissues than in tissues of the control group. The mean level of Lrig1 of the NP tissues was 22.2 ng/ml, while the mean level of the control group was 28.5 ng/ml. According to the results of ROC analysis, Lrig1 levels have the power to distinguish polyp tissues from control tissues (AUC=0.794). Lrig1 levels were higher in tissues with scores of 4-8 than in tissues with scores of 16-20 based on the results of computed tomography scoring. According to endoscopic evaluations, Lrig1 levels of tissues with scores of 5-8 or 9-11 were relatively lower than those of tissues with scores of 2-4. Conclusion: Lrig1 levels were found to be decreased in NP tissues. Thus, Lrig1 may be used to confirm the presence of NPs. Lrig1 may also be helpful in NP grading. Increasing the Lrig1 levels in cases of NPs has the potential to become a targetable treatment modality.

Aberrant promoter methylation contributes to LRIG1 silencing in basal/triple-negative breast cancer

BACKGROUND

LRIG1, the founding member of the LRIG (leucine-rich repeat and immunoglobulin-like domain) family of transmembrane proteins, is a negative regulator of receptor tyrosine kinases and a tumour suppressor. Decreased LRIG1 expression is consistently observed in cancer, across diverse tumour types, and is linked to poor patient prognosis. However, mechanisms by which LRIG1 is repressed are not fully understood. Silencing of LRIG1 through promoter CpG island methylation has been reported in colorectal and cervical cancer but studies in breast cancer remain limited.

METHODS

In silico analysis of human breast cancer patient data were used to demonstrate a correlation between DNA methylation and LRIG1 silencing in basal/triple-negative breast cancer, and its impact on patient survival. LRIG1 gene expression, protein abundance, and methylation enrichment were examined by quantitative reverse-transcription PCR, immunoblotting, and methylation immunoprecipitation, respectively, in breast cancer cell lines in vitro. We examined the impact of global demethylation on LRIG1 expression and methylation enrichment using 5-aza-2'-deoxycytidine. We also examined the effects of targeted demethylation of the LRIG1 CpG island, and transcriptional activation of LRIG1 expression, using the RNA guided deadCas9 transactivation system.

RESULTS

Across breast cancer subtypes, LRIG1 expression is lowest in the basal/triple-negative subtype so we investigated whether differential methylation may contribute to this. Indeed, we find that LRIG1 CpG island methylation is most prominent in basal/triple-negative cell lines and patient samples. Use of the global demethylating agent 5-aza-2'-deoxycytidine decreases methylation leading to increased LRIG1 transcript expression in basal/triple-negative cell lines, while having no effect on LRIG1 expression in luminal/ER-positive cell lines. Using a CRISPR/deadCas9 (dCas9)-based targeting approach, we demonstrate that TET1-mediated demethylation (Tet1-dCas9) along with VP64-mediated transcriptional activation (VP64-dCas9) at the CpG island, increased endogenous LRIG1 expression in basal/triple-negative breast cancer cells, without transcriptional upregulation at predicted off-target sites. Activation of LRIG1 by the dCas9 transactivation system significantly increased LRIG1 protein abundance, reduced site-specific methylation, and reduced cancer cell viability. Our findings suggest that CRISPR-mediated targeted activation may be a feasible way to restore LRIG1 expression in cancer.

CONCLUSIONS

Our study contributes novel insight into mechanisms which repress LRIG1 in triple-negative breast cancer and demonstrates for the first time that targeted de-repression of LRIG1 in cancer cells is possible. Understanding the epigenetic mechanisms associated with repression of tumour suppressor genes holds potential for the advancement of therapeutic approaches.

Lrig1 expression identifies airway basal cells with high proliferative capacity and restricts lung squamous cell carcinoma growth

Background

Lung squamous cell carcinoma (LUSC) accounts for a significant proportion of cancer deaths worldwide, and is preceded by the appearance of progressively disorganised pre-invasive lesions in the airway epithelium. Yet the biological mechanisms underlying progression of pre-invasive lesions into invasive LUSC are not fully understood. LRIG1 (leucine-rich repeats and immunoglobulin-like domains 1) is downregulated in pre-invasive airway lesions and invasive LUSC tumours and this correlates with decreased lung cancer patient survival.

Methods and results

Using an Lrig1 knock-in reporter mouse and human airway epithelial cells collected at bronchoscopy, we show that during homeostasis LRIG1 is heterogeneously expressed in the airway epithelium. In basal airway epithelial cells, the suspected cell of origin of LUSC, LRIG1 identifies a subpopulation of progenitor cells with higher in vitro proliferative and self-renewal potential in both the mouse and human. Using the N-nitroso-tris-chloroethylurea (NTCU)-induced murine model of LUSC, we find that Lrig1 loss-of-function leads to abnormally high cell proliferation during the earliest stages of pre-invasive disease and to the formation of significantly larger invasive tumours, suggesting accelerated disease progression.

Conclusion

Together, our findings identify LRIG1 as a marker of basal airway progenitor cells with high proliferative potential and as a regulator of pre-invasive lung cancer progression. This work highlights the clinical relevance of LRIG1 and the potential of the NTCU-induced LUSC model for functional assessment of candidate tumour suppressors and oncogenes.

LRIG1 is lost in development of squamous cell lung cancers. This study shows that LRIG1 marks basal airway progenitor cells with high proliferative potential and regulates progression of pre-invasive squamous cell lung cancer.https://bit.ly/3AbPtY3

The transmembrane protein LRIG1 triggers melanocytic tumor development following chemically induced skin carcinogenesis

The incidence of melanoma and nonmelanoma skin cancer has increased tremendously in recent years. Although novel treatment options have significantly improved patient outcomes, the prognosis for most patients with an advanced disease remains dismal. It is, thus, imperative to understand the molecular mechanisms involved in skin carcinogenesis in order to develop new targeted treatment strategies. Receptor tyrosine kinases (RTK) like the ERBB receptor family, including EGFR/ERBB1, ERBB2/NEU, ERBB3, and ERBB4, are important regulators of skin homeostasis and their dysregulation often results in cancer, which makes them attractive therapeutic targets. Members of the leucine‐rich repeats and immunoglobulin‐like domains protein family (LRIG1‐3) are ERBB regulators and thus potential therapeutic targets to manipulate ERBB receptors. Here, we analyzed the function of LRIG1 during chemically induced skin carcinogenesis in transgenic mice expressing LRIG1 in the skin under the control of the keratin 5 promoter (LRIG1‐TG mice). We observed a significant induction of melanocytic tumor formation in LRIG1‐TG mice and no difference in papilloma incidence between LRIG1‐TG and control mice. Our findings also revealed that LRIG1 affects ERBB signaling via decreased phosphorylation of EGFR and increased activation of the oncoprotein ERBB2 during skin carcinogenesis. The epidermal proliferation rate was significantly decreased during epidermal tumorigenesis under LRIG1 overexpression, and the apoptosis marker cleaved caspase 3 was significantly activated in the epidermis of transgenic LRIG1 mice. Additionally, we detected LRIG1 expression in human cutaneous squamous cell carcinoma and melanoma samples. Therefore, we depleted LRIG1 in human melanoma cells (A375) by CRISPR/Cas9 technology and found that this caused EGFR and ERBB3 downregulation in A375 LRIG1 knockout cells 6 h following stimulation with EGF. In conclusion, our study demonstrated that LRIG1‐TG mice develop melanocytic skin tumors during chemical skin carcinogenesis and a deletion of LRIG1 in human melanoma cells reduces EGFR and ERBB3 expression after EGF stimulation.

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

LRIG1, leucine-rich repeats and immunoglobulin-like domains protein 1, was discovered more than 20 years ago and has been shown to be downregulated or lost, and to function as a tumor suppressor in several cancers. Another well-reported biological function of LRIG1 is to regulate and help enforce the quiescence of adult stem cells (SCs). In both contexts, LRIG1 regulates SC quiescence and represses tumor growth via, primarily, antagonizing the expression and activities of ERBB and other receptor tyrosine kinases (RTKs). We have recently reported that in treatment-naïve human prostate cancer (PCa), LRIG1 is primarily regulated by androgen receptor (AR) and is prominently overexpressed. In castration-resistant PCa (CRPC), both LRIG1 and AR expression becomes heterogeneous and, frequently, discordant. Importantly, in both androgen-dependent PCa and CRPC models, LRIG1 exhibits tumor-suppressive functions. Moreover, LRIG1 induction inhibits the growth of pre-established AR⁺ and AR⁻ PCa. Here, upon a brief introduction of the LRIG1 and the LRIG family, we provide an updated overview on LRIG1 functions in regulating SC quiescence and repressing tumor development. We further highlight the expression, regulation and functions of LRIG1 in treatment-naïve PCa and CRPC. We conclude by offering the perspectives of identifying novel cancer-specific LRIG1-interacting signaling partners and developing LRIG1-based anti-cancer therapeutics and diagnostic/prognostic biomarkers.

LRIG1-Mediated Inhibition of EGF Receptor Signaling Regulates Neural Precursor Cell Proliferation in the Neocortex

Here, we ask how neural stem cells (NSCs) transition in the developing neocortex from a rapidly to a slowly proliferating state, a process required to maintain lifelong stem cell pools. We identify LRIG1, known to regulate receptor tyrosine kinase signaling in other cell types, as a negative regulator of cortical NSC proliferation. LRIG1 is expressed in murine cortical NSCs as they start to proliferate more slowly during embryogenesis and then peaks postnatally when they transition to give rise to a portion of adult NSCs. Constitutive or acute loss of Lrig1 in NSCs over this developmental time frame causes stem cell expansion due to increased proliferation. LRIG1 controls NSC proliferation by associating with and negatively regulating the epidermal growth factor receptor (EGFR). These data support a model in which LRIG1 dampens the stem cell response to EGFR ligands within the cortical environment to slow their proliferation as they transition to postnatal adult NSCs.

Dynamic heterogeneity influences the leader-follower dynamics during epithelial wound closure

Cells of epithelial tissue proliferate and pack together to attain an eventual density homeostasis. As the cell density increases, spatial distribution of velocity and force show striking similarity to the dynamic heterogeneity observed elsewhere in dense granular matter. While the physical nature of this heterogeneity is somewhat known in the epithelial cell monolayer, its biological relevance and precise connection to cell density remain elusive. Relevantly, we had demonstrated how large-scale dynamic heterogeneity in the monolayer stress field in the bulk could critically influence the emergence of leader cells at the wound margin during wound closure, but did not connect the observation to the corresponding cell density. In fact, numerous previous reports had essentially associated long-range force and velocity correlation with either cell density or dynamic heterogeneity, without any generalization. Here, we attempted to unify these two parameters under a single framework and explored their consequence on the dynamics of leader cells, which eventually affected the efficacy of collective migration and wound closure. To this end, we first quantified the dynamic heterogeneity by the peak height of four-point susceptibility. Remarkably, this quantity showed a linear relationship with cell density over many experimental samples. We then varied the heterogeneity, by changing cell density, and found this change altered the number of leader cells at the wound margin. At low heterogeneity, wound closure was slower, with decreased persistence, reduced coordination and disruptive leader-follower interactions. Finally, microscopic characterization of cell-substrate adhesions illustrated how heterogeneity influenced orientations of focal adhesions, affecting coordinated cell movements. Together, these results demonstrate the importance of dynamic heterogeneity in epithelial wound healing. This article is part of the theme issue 'Multi-scale analysis and modelling of collective migration in biological systems'.

A single-progenitor model as the unifying paradigm of epidermal and esophageal epithelial maintenance in mice

In adult skin epidermis and the epithelium lining the esophagus cells are constantly shed from the tissue surface and replaced by cell division. Tracking genetically labelled cells in transgenic mice has given insight into cell behavior, but conflicting models appear consistent with the results. Here, we use an additional transgenic assay to follow cell division in mouse esophagus and the epidermis at multiple body sites. We find that proliferating cells divide at a similar rate, and place bounds on the distribution cell cycle times. By including these results in a common analytic approach, we show that data from eight lineage tracing experiments is consistent with tissue maintenance by a single population of proliferating cells. The outcome of a given cell division is unpredictable but, on average, the likelihood of producing proliferating and differentiating cells is equal, ensuring cellular homeostasis. These findings are key to understanding squamous epithelial homeostasis and carcinogenesis.

LMO7 and LIMCH1 interact with LRIG proteins in lung cancer, with prognostic implications for early-stage disease

OBJECTIVES

The human leucine-rich repeats and immunoglobulin-like domains (LRIG) protein family comprises the integral membrane proteins LRIG1, LRIG2 and LRIG3. LRIG1 is frequently down-regulated in human cancer, and high levels of LRIG1 in tumor tissue are associated with favorable clinical outcomes in several tumor types including non-small cell lung cancer (NSCLC). Mechanistically, LRIG1 negatively regulates receptor tyrosine kinases and functions as a tumor suppressor. However, the details of the molecular mechanisms involved are poorly understood, and even less is known about the functions of LRIG2 and LRIG3. The aim of this study was to further elucidate the functions and molecular interactions of the LRIG proteins.

MATERIALS AND METHODS

A yeast two-hybrid screen was performed using a cytosolic LRIG3 peptide as bait. In transfected human cells, co-immunoprecipitation and co-localization experiments were performed. Proximity ligation assay was performed to investigate interactions between endogenously expressed proteins. Expression levels of LMO7 and LIMCH1 in normal and malignant lung tissue were investigated using qRT-PCR and through in silico analyses of public data sets. Finally, a clinical cohort comprising 355 surgically treated NSCLC cases was immunostained for LMO7.

RESULTS

In the yeast two-hybrid screen, the two paralogous proteins LMO7 and LIMCH1 were identified as interaction partners to LRIG3. LMO7 and LIMCH1 co-localized and co-immunoprecipitated with both LRIG1 and LRIG3. Endogenously expressed LMO7 was in close proximity of both LRIG1 and LRIG3. LMO7 and LIMCH1 were highly expressed in normal lung tissue and down-regulated in malignant lung tissue. LMO7 immunoreactivity was shown to be a negative prognostic factor in LRIG1 positive tumors, predicting poor patient survival.

CONCLUSION

These findings suggest that LMO7 and LIMCH1 physically interact with LRIG proteins and that expression of LMO7 is of clinical importance in NSCLC.

Lrig1 is a haploinsufficient tumor suppressor gene in malignant glioma

Recently, a genome-wide association study showed that a single nucleotide polymorphism (SNP) —rs11706832—in intron 2 of the human LRIG1 (Leucine-rich repeats and immunoglobulin-like domains 1) gene is associated with susceptibility to glioma. However, the mechanism by which rs11706832 affects glioma risk remains unknown; additionally, it is unknown whether the expression levels of LRIG1 are a relevant determinant of gliomagenesis. Here, we investigated the role of Lrig1 in platelet-derived growth factor (PDGF)-induced experimental glioma in mice by introducing mono-allelic and bi-allelic deletions of Lrig1 followed by inducing gliomagenesis via intracranial retroviral transduction of PDGFB in neural progenitor cells. Lrig1 was expressed in PDGFB-induced gliomas in wild-type mice as assessed using in situ hybridization. Intriguingly, Lrig1-heterozygous mice developed higher grade gliomas than did wild-type mice (grade IV vs. grade II/III, p = 0.002). Reciprocally, the ectopic expression of LRIG1 in the TB107 high-grade human glioma (glioblastoma, grade IV) cell line decreased the invasion of orthotopic tumors in immunocompromised mice in vivo and reduced cell migration in vitro. Concomitantly, the activity of the receptor tyrosine kinase MET was downregulated, which partially explained the reduction in cell migration. In summary, Lrig1 is a haploinsufficient suppressor of PDGFB-driven glioma, possibly in part via negative regulation of MET-driven cell migration and invasion. Thus, for the first time, changes in physiological Lrig1 expression have been linked to gliomagenesis, whereby the SNP rs11706832 may affect glioma risk by regulating LRIG1 expression.

A protein interaction network centered on leucine-rich repeats and immunoglobulin-like domains 1 (LRIG1) regulates growth factor receptors

Leucine-rich repeats and immunoglobulin-like domains 1 (LRIG1) is a tumor suppressor and a negative regulator of several receptor tyrosine kinases. The molecular mechanisms by which LRIG1 mediates its tumor suppressor effects and regulates receptor tyrosine kinases remain incompletely understood. Here, we performed a yeast two-hybrid screen to identify novel LRIG1-interacting proteins and mined data from the BioPlex (biophysical interactions of ORFeome-based complexes) protein interaction data repository. The putative LRIG1 interactors identified in the screen were functionally evaluated using a triple co-transfection system in which HEK293 cells were co-transfected with platelet-derived growth factor receptor α, LRIG1, and shRNAs against the identified LRIG1 interactors. The effects of the shRNAs on the ability of LRIG1 to down-regulate platelet-derived growth factor receptor α expression were evaluated. On the basis of these results, we present an LRIG1 protein interaction network with many newly identified components. The network contains the apparently functionally important LRIG1-interacting proteins RAB4A, PON2, GAL3ST1, ZBTB16, LRIG2, CNPY3, HLA-DRA, GML, CNPY4, LRRC40, and LRIG3, together with GLRX3, PTPRK, and other proteins. In silico analyses of The Cancer Genome Atlas data sets revealed consistent correlations between the expression of the transcripts encoding LRIG1 and its interactors ZBTB16 and PTPRK and inverse correlations between the transcripts encoding LRIG1 and GLRX3. We further studied the LRIG1 function–promoting paraoxonase PON2 and found that it co-localized with LRIG1 in LRIG1-transfected cells. The proposed LRIG1 protein interaction network will provide leads for future studies aiming to understand the molecular functions of LRIG1 and the regulation of growth factor signaling.

Downregulation of LRIG2 expression inhibits angiogenesis of glioma via EGFR/VEGF-A pathway

Active angiogenesis is the basic pathological feature of glioma. Tumor angiogenesis is involved in vascular endothelial cell migration to the tumor tissue and in the formation of tube-like structures. The present study aimed to investigate the role of leucine-rich repeats and immunoglobulin-like domains 2 (LRIG2) in glioma angiogenesis. Glioma (n=50) and normal brain (n=20) tissue samples were collected from patients to detect the expression of LRIG2, epidermal growth factor receptor (EGFR), vascular endothelial growth factor A (VEGF-A), and cluster of differentiation 31 (CD31) using immunohistochemistry. In addition, the association between the expression of LRIG2 in glioma tissue and the microvessel density (MVD) was analyzed. In vitro, the expression of LRIG2 in human glioma U87 and U251 cell lines was knocked down. Subsequently, cell migration and tube formation assays of human umbilical vein endothelial cells (HUVECs) were performed using a coculture system. The protein expression levels of LRIG2, EGFR, phosphorylated-EGFR and VEGF-A were determined using western blotting. The results demonstrated that the expression levels of LRIG2, EGFR, VEGF-A and CD31 were highly upregulated in glioma tissue samples. Furthermore, LRIG2 expression in glioma tissue samples was significantly correlated with the MVD. In vitro, the downregulation of LRIG2 inhibited HUVEC migration and tube formation induced by coculture with glioma cells. The downregulation of LRIG2 resulted in decreased expression of EGFR and VEGF-A. The effects of the LRIG2 knockdown were reversed following EGF treatment. These findings suggest that LRIG2 is a potential target for the inhibition of glioma angiogenesis, which is possibly mediated via the EGFR/VEGF-A signaling pathway.

Harnessing LRIG1-mediated inhibition of receptor tyrosine kinases for cancer therapy

Leucine-rich repeats and immunoglobulin-like domains containing protein 1 (LRIG1) is an endogenous feedback regulator of receptor tyrosine kinases (RTKs) and was recently shown to inhibit growth of different types of malignancies. Additionally, this multifaceted RTK inhibitor was reported to be a tumor suppressor, a stem cell regulator, and a modulator of different cellular phenotypes. This mini-review provides a concise and up-to-date summary about the known functions of LRIG1 and its related family members, with a special emphasis on underlying molecular mechanisms and the opportunities for harnessing its therapeutic potential against cancer.

An FGFR1-SPRY2 Signaling Axis Limits Basal Cell Proliferation in the Steady-State Airway Epithelium

The steady-state airway epithelium has a low rate of stem cell turnover but can nevertheless mount a rapid proliferative response following injury. This suggests a mechanism to restrain proliferation at steady state. One such mechanism has been identified in skeletal muscle in which pro-proliferative FGFR1 signaling is antagonized by SPRY1 to maintain satellite cell quiescence. Surprisingly, we found that deletion of Fgfr1 or Spry2 in basal cells of the adult mouse trachea caused an increase in steady-state proliferation. We show that in airway basal cells, SPRY2 is post-translationally modified in response to FGFR1 signaling. This allows SPRY2 to inhibit intracellular signaling downstream of other receptor tyrosine kinases and restrain basal cell proliferation. An FGFR1-SPRY2 signaling axis has previously been characterized in cell lines in vitro. We now demonstrate an in vivo biological function of this interaction and thus identify an active signaling mechanism that maintains quiescence in the airway epithelium.

LRIG1 opposes epithelial-to-mesenchymal transition and inhibits invasion of basal-like breast cancer cells

LRIG1, a member of the LRIG family of transmembrane leucine rich repeat-containing proteins, is a negative regulator of receptor tyrosine kinase signaling and a tumor suppressor. LRIG1 expression is broadly decreased in human cancer and in breast cancer, low expression of LRIG1 has been linked to decreased relapse-free survival. Recently, low expression of LRIG1 was revealed to be an independent risk factor for breast cancer metastasis and death. These findings suggest that LRIG1 may oppose breast cancer cell motility and invasion, cellular processes which are fundamental to metastasis. However, very little is known of LRIG1 function in this regard. In this study, we demonstrate that LRIG1 is down-regulated during epithelial to mesenchymal transition (EMT) of human mammary epithelial cells, suggesting that LRIG1 expression may represent a barrier to EMT. Indeed, depletion of endogenous LRIG1 in human mammary epithelial cells expands the stem cell population, augments mammosphere formation and accelerates EMT. Conversely, expression of LRIG1 in highly invasive Basal B breast cancer cells provokes a mesenchymal to epithelial transition accompanied by a dramatic suppression of tumorsphere formation and a striking loss of invasive growth in three-dimensional culture. LRIG1 expression perturbs multiple signaling pathways and represses markers and effectors of the mesenchymal state. Furthermore, LRIG1 expression in MDA-MB-231 breast cancer cells significantly slows their growth as tumors, providing the first in vivo evidence that LRIG1 functions as a growth suppressor in breast cancer.

Clonal Dynamics Reveal Two Distinct Populations of Basal Cells in Slow-Turnover Airway Epithelium

Epithelial lineages have been studied at cellular resolution in multiple organs that turn over rapidly. However, many epithelia, including those of the lung, liver, pancreas, and prostate, turn over slowly and may be regulated differently. We investigated the mouse tracheal epithelial lineage at homeostasis by using long-term clonal analysis and mathematical modeling. This pseudostratified epithelium contains basal cells and secretory and multiciliated luminal cells. Our analysis revealed that basal cells are heterogeneous, comprising approximately equal numbers of multipotent stem cells and committed precursors, which persist in the basal layer for 11 days before differentiating to luminal fate. We confirmed the molecular and functional differences within the basal population by using single-cell qRT-PCR and further lineage labeling. Additionally, we show that self-renewal of short-lived secretory cells is a feature of homeostasis. We have thus revealed early luminal commitment of cells that are morphologically indistinguishable from stem cells.

LRIG1 enhances the radiosensitivity of radioresistant human glioblastoma U251 cells via attenuation of the EGFR/Akt signaling pathway

The radiotherapy as a local and regional modality is widely applied in treatment of glioma, but most glioblastomas are commonly resistant to irradiation treatment. It remains challengeable to seek out efficient strategies to conquer the resistance of human glioblastoma cells to radiotherapy. Leucine-rich repeats and immunoglobulin-like domains protein 1 (LRIG1) is a newly discovered tumor suppressor which involved in regulation of chemosensitivity in various human cancer cells. In the present study, we established a radioresistant U251 cell line (U251R) to investigate the role of LRIG1 in regulation of radiosensitivity in human glioblastoma cells. Significantly decreased expression level of LRIG1 and enhanced expression of EGFR and phosphorylated Akt were detected in U251R cells compared with the parental U251 cells. U251R cells exhibited an advantage in colony formation ability, which accompanied by remarkably reduced X-ray-induced γ-H2AX foci formation and cell apoptosis. LRIG1 overexpression significantly inhibited the colony formation ability of U251R cells and obviously enhanced X-ray-inducedγ-H2AX foci formation and cell apoptosis. In addition, up-regulated expression of LRIG1 suppressed the expression level of EGFR and phosphorylated Akt protein. Our results demonstrated that LRIG1 expression was related to the radiosensitivity of human glioblastoma cells and may play an important role in the regulation of cellular radiosensitivity of human glioblastoma cells through the EGFR/Akt signaling pathway.

LRIG1 is a prognostic biomarker in non-small cell lung cancer

BACKGROUND

The leucine-rich repeats and immunoglobulin-like domains (LRIG) family of transmembrane proteins are involved in the regulation of cellular signal transduction. LRIG1 is an endogenous inhibitor of receptor tyrosine kinases (RTKs) and an emerging tumor suppressor. In the lung epithelium, the expression of LRIG1 is downregulated by tobacco smoking, and further downregulated in lung squamous cell carcinoma.

MATERIAL AND METHODS

The expression of LRIG proteins were analyzed in 347 cases of non-small cell lung cancer (NSCLC) by immunohistochemistry, and LRIG1 mRNA expression was evaluated in 807 lung cancer samples in silico in the Oncomine database. Potential associations between the expression data and the clinical parameters, including patient survival, were investigated.

RESULTS

Expression of the LRIG1 protein was found to be an independent prognostic factor in NSCLC, whereas expression of LRIG2 or LRIG3 did not correlate with patient survival. The levels of LRIG1 mRNA also correlated with the survival of NSCLC patients.

CONCLUSION

These findings demonstrate that LRIG1 is an independent prognostic factor in patients with NSCLC that could be important in future decision-making algorithms for adjuvant lung cancer treatment.

LRIG1 extracellular domain: structure and function analysis

We have expressed and purified three soluble fragments of the human LRIG1-ECD (extracellular domain): the LRIG1-LRR (leucine-rich repeat) domain, the LRIG1-3Ig (immunoglobulin-like) domain, and the LRIG1-LRR-1Ig fragment using baculovirus vectors in insect cells. The two LRIG1 domains crystallised so that we have been able to determine the three-dimensional structures at 2.3Å resolution. We developed a three-dimensional structure for the LRIG1-ECD using homology modelling based on the LINGO-1 structure. The LRIG1-LRR domain and the LRIG1-LRR-1Ig fragment are monomers in solution, whereas the LRIG1-3Ig domain appears to be dimeric. We could not detect any binding of the LRIG1 domains or the LRIG1-LRR-1Ig fragment to the EGF receptor (EGFR), either in solution using biosensor analysis or when the EGFR was expressed on the cell surface. The FLAG-tagged LRIG1-LRR-1Ig fragment binds weakly to colon cancer cells regardless of the presence of EGFRs. Similarly, neither the soluble LRIG1-LRR nor the LRIG1-3Ig domains nor the full-length LRIG1 co-expressed in HEK293 cells inhibited ligand-stimulated activation of cell-surface EGFR.

Biodegradable polymeric gene delivering nanoscale hybrid micelles enhance the suppression effect of LRIG1 in breast cancer

Biodegradable polymeric gene delivering nanoscale hybrid micelles enhance the suppression effect of LRIG1 in breast cancer.

LRIG and cancer prognosis

BACKGROUND

Optimal treatment decisions for cancer patients require reliable prognostic and predictive information. However, this information is inadequate in many cases. Several recent studies suggest that the leucine-rich repeats and immunoglobulin-like domains (LRIG) genes, transcripts, and proteins have prognostic implications in various cancer types.

MATERIAL AND METHODS

Relevant literature was identified on PubMed using the key words lrig1, lrig2, and lrig3. LRIG mRNA expression in cancer versus normal tissues was investigated using the Oncomine database.

RESULTS

The three human LRIG genes, LRIG1, LRIG2, and LRIG3, encode single-pass transmembrane proteins. LRIG1 is a negative regulator of growth factor signaling that has been shown to function as a tumor suppressor in vitro and in vivo in mice. The functions of LRIG2 and LRIG3 are less well defined. LRIG gene and protein expression are commonly dysregulated in human cancer. In early stage breast cancer, LRIG1 copy number was recently shown to predict early and late relapse in addition to overall survival; in nasopharyngeal carcinoma, loss of LRIG1 is also associated with poor survival. LRIG gene and protein expression have prognostic value in breast cancer, uterine cervical cancer, head-and-neck cancer, glioma, non-small cell lung cancer, prostate cancer, and cutaneous squamous cell carcinoma. In general, expression of LRIG1 and LRIG3 is associated with good survival, whereas expression of LRIG2 is associated with poor survival. Additionally, LRIG1 regulates cellular sensitivity to anti-cancer drugs, which indicates a possible role as a predictive marker.

CONCLUSIONS

LRIG gene statuses and mRNA and protein expression are clinically relevant prognostic indicators in several types of human cancer. We propose that LRIG analyses could become important when making informed and individualized clinical decisions regarding the management of cancer patients.

LRIG1 enhances chemosensitivity by modulating BCL-2 expression and receptor tyrosine kinase signaling in glioma cells

PURPOSE

Leucine-rich repeats and immunoglobulin-like domains 1 (LRIG1) are an inhibitor of receptor tyrosine kinases (RTKs) that was discovered in recent years, and many studies showed that LRIG1 is a tumor suppressor gene and may be related to tumor drug resistance. In this study, we explored whether LRIG1 protein expression can improve the chemosensitivity of glioma cells and what was its mechanism.

MATERIALS AND METHODS

We collected 93 cases of glioma tissues and detected the expression of LRIG1 and BCL-2. We constructed a multidrug resistance cell line U251/multidrug resistance (MDR) and examined the change of LRIG1 and BCL-2 at mRNA and protein expression levels. LRIG1 expression was upregulated in U251/MDR cells and we detected the change of multidrug resistance. Meanwhile, we changed the expression of LRIG1 and BCL-2 and explored the relationship between LRIG1 and BCL-2. Finally, we also explored the relationship between LRIG1 and RTKs.

RESULTS

LRIG1 was negatively correlated with BCL-2 expression in glioma tissue and U251/MDR cells, and upregulation of LRIG1 can enhance chemosensitivity and inhibit BCL-2 expression. Furthermore, LRIG1 was negatively correlated with RTKs in U251/MDR cells.

CONCLUSION

These results demonstrated that LRIG1 can improve chemosensitivity by modulating BCL-2 expression and RTK signaling in glioma cells.

LRIG1 as a potential novel marker for neoplastic transformation in ocular surface squamous neoplasia

The leucine rich repeats and immunoglobulin-like protein 1 (LRIG1) is a newly discovered negative regulator of epidermal growth factor receptor (EGFR) and a proposed tumor suppressor. It is not universally downregulated in human cancers, and its role in neoplastic transformation and tumorigenesis is not well-documented. In this study, we show the expression of LRIG1 as a novel potential marker for neoplastic transformation in ocular-surface squamous neoplasia (OSSN). The following two groups were included in this study: 1) benign group (3 cases; 1 with papilloma and 2 with dysplasia) and 2) malignant group (3 cases with squamous cell carcinoma (SCC)). In both groups, immunofluorescence analysis was firstly performed for keratins 4, 12, 13, and 15 to characterize the state of differentiation, and for Ki67 to evaluate the proliferation activity. Subsequently, LRIG1 and EGFR expression was analyzed. Either keratin 4 and/or 13, both non-keratinized epithelial cell markers, were generally expressed in both groups, except for 1 severe SCC case. Keratin 15, an undifferentiated basal cell marker, was more strongly expressed in the malignant cases than in the benign cases. The Ki67 index was significantly higher (P<0.002) in the malignant group (33.2%) than in the benign group (10.9%). LRIG1 expression was limited to basal epithelial cells in normal corneal epithelial tissue. Interestingly, LRIG1 was expressed throughout the epithelium in all the benign cases. In contrast, its expression was limited or totally disappeared in the malignant cases. Inversely, EGFR staining was faintly expressed in the benign cases, yet strongly expressed in the malignant cases. Malignant tissue with proliferative potential presented EGFR overexpression and inverse downregulation of LRIG1, consistent with LRIG1 being a suppressor of neoplastic transformation by counteracting the tumor growth property of EGFR. Our findings indicate that downregulation of LRIG1 is possibly a novel potential marker of transformation and tumorigenesis in OSSN cases.

Targeting EGFR signalling in chronic lung disease: therapeutic challenges and opportunities

Chronic respiratory diseases, including pulmonary fibrosis, chronic obstructive pulmonary disease (COPD) and lung cancer, are the second leading cause of death among Europeans. Despite this, there have been only a few therapeutic advances in these conditions over the past 20 years. In this review we provide evidence that targeting the epidermal growth factor receptor (EGFR) signalling pathway may represent a novel therapeutic panacea for treating chronic lung disease. Using evidence from human patient samples, transgenic animal models, and cell and molecular biology studies we highlight the roles of this signalling pathway in lung development, homeostasis, repair, and disease ontogeny. We identify mechanisms underlying lung EGFR pathway regulation and suggest how targeting these mechanisms using new and existing therapies has the potential to improve future lung cancer, COPD and pulmonary fibrosis patient outcomes.

The LRIG family: enigmatic regulators of growth factor receptor signaling

The leucine-rich repeats and immunoglobulin-like domains (LRIG) family of transmembrane proteins contains three vertebrate members (LRIG1, LRIG2 and LRIG3) and one member each in flies (Lambik) and worms (Sma-10). LRIGs have stepped into the spotlight as essential regulators of growth factor receptors, including receptor tyrosine and serine/threonine kinases. LRIGs have been found to both negatively (LRIG1 and LRIG3) and positively (Sma-10 and LRIG3) regulate growth factor receptor expression and signaling, although the precise molecular mechanisms by which LRIGs function are not yet understood. The most is known about LRIG1, which was recently demonstrated to be a tumor suppressor. Indeed, in vivo experiments reinforce the essential link between LRIG1 and repression of its targets for tissue homeostasis. LRIG1 has also been identified as a stem cell marker and regulator of stem cell quiescence in a variety of tissues, discussed within. Comparably, less is known about LRIG2 and LRIG3, although studies to date suggest that their functions are largely distinct from that of LRIG1 and that they likely do not serve as growth/tumor suppressors. Finally, the translational applications of expressing soluble forms of LRIG1 in LRIG1-deficient tumors are being explored and hold tremendous promise.

The epidermis comprises autonomous compartments maintained by distinct stem cell populations

The complex anatomy of the epidermis contains multiple adult stem cell populations, but the extent to which they functionally overlap during homeostasis, wound healing, and tumor initiation remains poorly defined. Here, we demonstrate that Lrig1(+ve) cells are highly proliferative epidermal stem cells. Long-term clonal analysis reveals that Lrig1(+ve) cells maintain the upper pilosebaceous unit, containing the infundibulum and sebaceous gland as independent compartments, but contribute to neither the hair follicle nor the interfollicular epidermis, which are maintained by distinct stem cell populations. In contrast, upon wounding, stem cell progeny from multiple compartments acquire lineage plasticity and make permanent contributions to regenerating tissue. We further show that oncogene activation in Lrig1(+ve) cells drives hyperplasia but requires auxiliary stimuli for tumor formation. In summary, our data demonstrate that epidermal stem cells are lineage restricted during homeostasis and suggest that compartmentalization may constitute a conserved mechanism underlying epithelial tissue maintenance.

Beyond the niche: tissue-level coordination of stem cell dynamics

Adult animals rely on populations of stem cells to ensure organ function throughout their lifetime. Stem cells are governed by signals from stem cell niches, and much is known about how single niches promote stemness and direct stem cell behavior. However, most organs contain a multitude of stem cell-niche units, which are often distributed across the entire expanse of the tissue. Beyond the biology of individual stem cell-niche interactions, the next challenge is to uncover the tissue-level processes that orchestrate spatial control of stem-based renewal, repair, and remodeling throughout a whole organ. Here we examine what is known about higher order mechanisms for interniche coordination in epithelial organs, whose simple geometry offers a promising entry point for understanding the regulation of niche number, distribution, and activity. We also consider the potential existence of stem cell territories and how tissue architecture may influence niche coordination.