LRIG1 and epidermal growth factor receptor in renal cell carcinoma: a quantitative RT--PCR and immunohistochemical analysis

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.

High-throughput functional screen identifies YWHAZ as a key regulator of pancreatic cancer metastasis

Pancreatic cancer is a leading cause of cancer death due to its early metastasis and limited response to the current therapies. Metastasis is a complicated multistep process, which is determined by complex genetic alterations. Despite the identification of many metastasis-related genes, distinguishing the drivers from numerous passengers and establishing the causality in cancer pathophysiology remains challenging. Here, we established a high-throughput and piggyBac transposon-based genetic screening platform, which enables either reduced or increased expression of chromosomal genes near the incorporation site of the gene search vector cassette that contains a doxycycline-regulated promoter. Using this strategy, we identified YWHAZ as a key regulator of pancreatic cancer metastasis. We demonstrated that functional activation of Ywhaz by the gene search vector led to enhanced metastatic capability in mouse pancreatic cancer cells. The metastasis-promoting role of YWHAZ was further validated in human pancreatic cancer cells. Overexpression of YWHAZ resulted in more aggressive metastatic phenotypes in vitro and a shorter survival rate in vivo by modulating epithelial-to-mesenchymal transition. Hence, our study established a high-throughput screening method to investigate the functional relevance of novel genes and validated YWHAZ as a key regulator of pancreatic cancer metastasis.

EGFR signaling pathway as therapeutic target in human cancers

Epidermal Growth Factor Receptor (EGFR) enacts major roles in the maintenance of epithelial tissues. However, when EGFR signaling is altered, it becomes the grand orchestrator of epithelial transformation, and hence one of the most world-wide studied tyrosine kinase receptors involved in neoplasia, in several tissues. In the last decades, EGFR-targeted therapies shaped the new era of precision-oncology. Despite major advances, the dream of converting solid tumors into a chronic disease is still unfulfilled, and long-term remission eludes us. Studies investigating the function of this protein in solid malignancies have revealed numerous ways how tumor cells dysregulate EGFR function. Starting from preclinical models (cell lines, organoids, murine models) and validating in clinical specimens, EGFR-related oncogenic pathways, mechanisms of resistance, and novel avenues to inhibit tumor growth and metastatic spread enriching the therapeutic portfolios, were identified. Focusing on non-small cell lung cancer (NSCLC), where EGFR mutations are major players in the adenocarcinoma subtype, we will go over the most relevant discoveries that led us to understand EGFR and beyond, and highlight how they revolutionized cancer treatment by expanding the therapeutic arsenal at our disposal.

Soluble LRIG2 is a potential biomarker for type 2 diabetes mellitus

Background

Early diagnosis and treatment of type 2 diabetes can delay the onset of microvascular and macrovascular complications. Therefore, the identification of a novel biomarker for diagnosing diabetes is necessary. In the present study, the role of serum soluble leucine-rich repeats and immunoglobulin like domains 2 (sLRIG2) was investigated as a diagnostic biomarker of type 2 diabetes.

Methods

A total of 240 subjects with newly diagnosed type 2 diabetes (n=80), prediabetes (n=80), or normal glucose tolerance (NGT; n=80) were included in this study. The fasting serum sLRIG2 level was measured using a quantitative sandwich enzyme immunoassay technique with an enzyme-linked immunosorbent assay (ELISA). Serum sLRIG2 levels were compared among the three groups, and the associations of serum sLRIG2 levels with clinical variables were investigated.

Results

Serum sLRIG2 levels were significantly higher in subjects with type 2 diabetes (16.7±8.0 ng/mL) than in subjects without diabetes (NGT group: 12.3±5.3 ng/mL, P<0.001; prediabetes group: 13.2±5.8 ng/mL, P=0.002). Glycosylated hemoglobin (HbA1c: r=0.378, P<0.001) and blood glucose (fasting: r=0.421, P<0.001; 2-hour postprandial: r=0.433, P<0.001) correlated more strongly with sLRIG2 than any other clinical variables.

Conclusions

The serum sLRIG2 levels correlated with glucose parameters; thus, sLRIG2 might be a novel diagnostic biomarker for type 2 diabetes.

Expression of LRIG1, a Negative Regulator of EGFR, Is Dynamically Altered during Different Stages of Gastric Carcinogenesis

Leucine-rich repeats and immunoglobulin-like domains (LRIG)-1 is a transmembrane protein that antagonizes epidermal growth factor receptor signaling in epithelial tissues. LRIG1 is down-regulated in various epithelial cancers, including bladder, breast, and colorectal cancer, suggesting that it functions as a tumor suppressor. However, its role in gastric carcinogenesis is not well understood. Here, we investigated the changes in LRIG1 expression during the stages of gastric cancer. We used a DMP-777-induced spasmolytic polypeptide-expressing metaplasia mouse model and a tissue array of human gastric cancer lesions. The effects of LRIG1 knockdown were also assessed using the human gastric cancer cell line SNU638 in a xenograft model. LRIG1 expression varied over the course of gastric carcinogenesis, increasing in spasmolytic polypeptide-expressing metaplasia lesions but disappearing in intestinal metaplasia and cancer lesions, and the increase was concurrent with the up-regulation of epidermal growth factor receptor. In addition, LRIG1 knockdown promoted the tumorigenic potential in vitro, which was manifested as increased proliferation, invasiveness, and migration as well as increased tumor size in vivo in the xenograft model. Furthermore, LRIG1 expression was determined to be a positive prognostic biomarker for the survival of gastric cancer patients. Collectively, our findings indicate that LRIG1 expression is closely related wto gastric carcinogenesis and may play a vital role as a tumor suppressor through the modulation of epidermal growth factor receptor activity.

Negative Regulation of Receptor Tyrosine Kinase (RTK) Signaling: A Developing Field

Trophic factors control cellular physiology by activating specific receptor tyrosine kinases (RTKs). While the over activation of RTK signaling pathways is associated with cell growth and cancer, recent findings support the concept that impaired down-regulation or deactivation of RTKs may also be a mechanism involved in tumor formation. Under this perspective, the molecular determinants of RTK signaling inhibition may act as tumor-suppressor genes and have a potential role as tumor markers to monitor and predict disease progression. Here, we review the current understanding of the physiological mechanisms that attenuate RTK signaling and discuss evidence that implicates deregulation of these events in cancer.

MicroRNA-590-3p enhances the radioresistance in glioblastoma cells by targeting LRIG1

microRNA (miR)-590 has been found to serve potential roles in cancer development; however, the expression and function of miR-590 in human gliomas remains to be elucidated. The present study aimed to investigate the expression of miR-590 in human glioma tissues and radioresistant human glioblastoma cells (U251R), and to determine the effect and related molecular mechanism of miR-590-3p on the radiosensitivity of U251R cells in vitro. The results from reverse transcription-quantitative polymerase chain reaction indicated that miR-590-3p was upregulated in human glioma tissues and radioresistant human glioblastoma cells, and that miR-590-3p expression was higher in high grade than in low grade gliomas. In vitro experiments revealed that the miR-590-3p inhibitor enhanced the radiosensitivity of U251R cells by suppressing cell viability, decreasing colony formation capacity and increasing cell apoptosis rate, as demonstrated by MTT, colony formation and flow cytometry analyses. A luciferase reporter assay demonstrated that leucine-rich repeats and immunoglobulin-like domains protein 1 (LRIG1) was a direct target of miR-590-3p. Furthermore, it was demonstrated that the effect of miR-590-3p suppression on cell viability, colony formation capacity and cell apoptosis rate was attenuated by the knockdown of LRIG1 in the U251R cells. In conclusion, the present study revealed that miR-590-3p was upregulated in human glioma tissues and radioresistant human glioblastoma cells, and miR-590-3p contributes to the radioresistance of human glioblastoma cells by directly targeting LRIG1. These findings may provide potential therapeutic strategies to prevent radioresistance in human gliomas.

Expression of LRIG1 is Associated With Good Prognosis for Human Non-small Cell Lung Cancer

Somatic mutations, which are associated with a certain rate of response to targeted therapies, are ubiquitously found in human non-small cell lung cancer (NSCLC). However, it is largely unknown which group of patients may benefit from the respective treatments targeting different somatic mutations. Therefore, more effective prognostic and predictive markers are desperately needed for the treatment of NSCLC harboring different somatic mutations. The leucine-rich repeats and immunoglobulin-like domains (LRIG)-1 is a tumor suppressor gene that belongs to the LRIG family. LRIG1 expression has prognostic significance in various human cancers.In this study, we first used the quantitative polymerase chain reaction (qPCR) and immunohistochemical analysis of 36 and 182 NSCLC patient tissues to analyze the LRIG1 expression respectively. To investigate the prognostic value of LRIG1 in NSCLC, we examined the correlation between clinical features and overall survival (OS) with Cox proportional hazard regression. We also compared the sensitivity and specificity of LRIG1 in NSCLC prognosis by logistic regression to further evaluate the prognostic efficiency of LRIG1 in NSCLC.We found that the LRIG1 expression was associated with pathological type, differentiation status, and stage of NSCLC. The result showed that LRIG1 was an independent prognostic factor for OS of NSCLC patients. LRIG1 in combination with other clinicopathological risk factors was a stronger prognostic model than clinicopathological risk factors alone.Thus, the LRIG1 expression potentially offered a significant clinical value in directing personal treatment for NSCLC patients.

LRIG1, a 3p tumor suppressor, represses EGFR signaling and is a novel epigenetic silenced gene in colorectal cancer

Downregulation of LRIG1 was found in many types of cancer. However, data concerning the possible mechanism of LRIG1 reduction in cancers were not reported yet. To analyze the regulation and function of LRIG1 in colorectal cancer (CRC), 6 cell lines, 46 paired tissues from primary CRC cases were employed in this study. In CRC cell lines, under-expression of LRIG1 was correlated with promoter region hypermethylation, and restoration of LRIG1 was induced by 5-Aza-2'-deoxyazacytidine treatment. Subsequently, we ectopically expressed LRIG1 in LRIG1 low-expressing HCT-116 cells and suppressed LRIG1 in LRIG1 high-expressing LoVo cells. We found that over-expression of LRIG1 inhibits cell proliferation and colony formation and tumor growth, while knockdown of LRIG1 promotes cell proliferation and colony formation. Decreased and increased EGFR/AKT signaling pathway may partially explain the lower and higher rates of proliferation in CRC cells transfected with LRIG1 cDNA or shRNA. In clinical samples, we compared the methylation, mRNA and protein expression of LRIG1 in samples of CRC tissues. A significant increase in LRIG1 methylation was identified in CRC specimens compared to adjacent normal tissues and that it was negatively correlated with its mRNA and protein expression. In conclusion, LRIG1 is frequently methylated in human CRC and consequent mRNA and protein downregulation may contribute to tumor growth by activating EGFR/AKT signaling.

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.

Lung Tumor Suppressor GPRC5A Binds EGFR and Restrains Its Effector Signaling

GPRC5A is a G-protein-coupled receptor expressed in lung tissue but repressed in most human lung cancers. Studies in Gprc5a(-/-) mice have established its role as a tumor-suppressor function in this setting, but the basis for its role has been obscure. Here, we report that GPRC5A functions as a negative modulator of EGFR signaling. Mouse tracheal epithelial cells (MTEC) from Gprc5a(-/-) mice exhibited a relative increase in EGFR and downstream STAT3 signaling, whereas GPRC5A expression inhibited EGFR and STAT3 signaling. GPRC5A physically interacted with EGFR through its transmembrane domain, which was required for its EGFR inhibitory activity. Gprc5a(-/-) MTEC were much more susceptible to EGFR inhibitors than wild-type MTEC, suggesting their dependence on EGFR signaling for proliferation and survival. Dysregulated EGFR and STAT3 were identified in the normal epithelia of small and terminal bronchioles as well as tumors of Gprc5a(-/-) mouse lungs. Moreover, in these lungs EGFR inhibitor treatment inhibited EGFR and STAT3 activation along with cell proliferation. Finally, overexpression of ectopic GPRC5A in human non-small cell lung carcinoma cells inhibited both EGF-induced and constitutively activated EGFR signaling. Taken together, our results show how GPRC5A deficiency leads to dysregulated EGFR and STAT3 signaling and lung tumorigenesis. Cancer Res; 75(9); 1801-14. ©2015 AACR.

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.

LRIG2 expression and prognosis in non-small cell lung cancer

The human leucine-rich repeats and immunoglobulin-like domains 2 (LRIG2) protein has been shown to be of prognostic value in several types of human cancer, however, the expression profiles of LRIG2 have not been described in non-small cell lung cancer (NSCLC). The present study evaluated the mRNA expression of LRIG2 in tumor specimens obtained from 39 NSCLC patients by SYBR Green quantitative polymerase chain reaction and the protein expression of LRIG2 in formalin-fixed paraffin sections obtained from 116 NSCLC patients by immunohistochemistry. The correlations between LRIG2 expression and clinicopathological data were analyzed. The patient survival data were collected retrospectively and the possible prognostic value of LRIG2 protein expression was investigated. The results showed that the mRNA expression of LRIG2 was decreased in NSCLC cancer tissues, which was associated with histological subtypes and tumor differentiation status. The protein expression of LRIG2 was only observed in the cytoplasm of the tumor tissue, which conformed to the mRNA expression results. Furthermore, the patients with high LRIG2 cytoplasmic expression showed poor survival times, and the five-year survival rate for patients with high LRIG2 expression was 27.8%, compared with 38.8% for patients with low expression (P=0.034), indicating that LRIG2 expression levels may have a potential role in the pathogenesis of NSCLC, and also a significant prognostic value. Further studies are required to fully elucidate the exact function of LRIG2 in NSCLC.

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.

Restoration of LRIG1 suppresses bladder cancer cell growth by directly targeting EGFR activity

Background

Recently, leucine-rich repeats and immunoglobulin-like domains 1 (LRIG1), a negative regulator of EGFR, was discovered is a novel agent for suppressing bladder cancer. The aim of this study was to investigate the impact of LRIG1 on the biological features of aggressive bladder cancer cells and the possible mechanisms of enhanced apoptosis induced by upregulation of LRIG1.

Methods

In this study, we examined the mRNA and protein expression of LRIG1 and EGFR in bladder cancers and normal bladder. Meanwhile, we overexpressed LRIG1 with adenovirus vector in T24/5637 bladder cancer cell lines, and we used real time-PCR, western blot, and co-immunoprecipitation analysis in order to examine the effects of LRIG1 gene on EGFR. Furthermore, we evaluate the impact of LRIG1 gene on the function of human bladder cancer cells and EGFR signaling.

Results

The expression of LRIG1 was decreased, while the expression of EGFR was increased in the majority of bladder cancer, and the ratio of EGFR/LRIG1 was increased in tumors versus normal tissue. We found that upregulation of LRIG1 induced cell apoptosis and cell growth inhibition, and further reversed invasion in bladder cancer cell lines in vitro by inhibiting phosphorylation of downstream MAPK and AKT signaling pathway.

Conclusion

Taken together, our findings provide us with an insight into LRIG1 function, and we conclude that LRIG1 evolved in bladder cancer as a rare feedback negative attenuator of EGFR, thus could offer a novel therapeutic target to treat patients with bladder cancer.

LRIG1 dictates the chemo-sensitivity of temozolomide (TMZ) in U251 glioblastoma cells via down-regulation of EGFR/topoisomerase-2/Bcl-2

In the current study, we aimed to understand the potential role of leucine-rich repeats and immunoglobulin-like domains 1 (LRIG1) in TMZ-resistance of U251 glioma cells. We established TMZ-resistant U251 clones (U251/TMZ cells), which expressed low level of LRIG1, but high levels of epidermal growth factor receptor (EGFR), topoisomerase-2 (Topo-2) and Bcl-2. Depletion of LRIG1 by the targeted RNA interference (RNAi) upregulated EGFR/Topo-2/Bcl-2 in U251 cells, and the cells were resistant to TMZ. Reversely, over-expression of LRIG1 in U251 cells downregulated EGFR/Topo-2/Bcl-2 expressions, and cells were hyper-sensitive to TMZ. Our data suggested EGFR-dependent mammalian target of rapamycin (mTOR) activation was important for Topo-2 and Bcl-2 expressions in U251/TMZ cells. The EGFR inhibitor and the mTOR inhibitor downregulated Topo-2/Bcl-2 expressions, both inhibitors also restored TMZ sensitivity in U251/TMZ cells. Finally, inhibition of Topo-2 or Bcl-2 by targeted RNAi(s) knockdown or by the corresponding inhibitor re-sensitized U251/TMZ cells to TMZ, indicating that both Topo-2 and Bcl-2 were important for TMZ resistance in the resistant U251 cells. Based on these results, we concluded that LRIG1 inhibits EGFR expression and the downstream signaling activation, interferes with Bcl-2/Topo-2 expressions and eventually sensitizes glioma cells to TMZ.

Leucine-rich repeat and immunoglobulin domain-containing protein-1 (Lrig1) negative regulatory action toward ErbB receptor tyrosine kinases is opposed by leucine-rich repeat and immunoglobulin domain-containing protein 3 (Lrig3)

Lrig1 is the founding member of the Lrig family of transmembrane leucine-rich repeat proteins, which also includes Lrig2 and Lrig3. Lrig1 is a negative regulator of oncogenic receptor tyrosine kinases, including ErbB and Met receptors, and promotes receptor degradation. Lrig1 has recently emerged as both a tumor suppressor and a key regulator of epidermal and epithelial stem cell quiescence. Despite this, little is known of the mechanisms by which Lrig1 is regulated. Lrig3 was recently reported to increase ErbB receptor expression suggesting that it may function in a manner opposite to Lrig1. In this study, we explore the interaction between Lrig1 and Lrig3 and demonstrate that Lrig1 and Lrig3 functionally oppose one another. Lrig3 opposes Lrig1 negative regulatory activity and stabilizes ErbB receptors. Conversely, Lrig1 destabilizes Lrig3, limiting Lrig3's positive effects on receptors and identifying Lrig3 as a new target of Lrig1. These studies provide new insight into the regulation of Lrig1 and uncover a complex cross-talk between Lrig1 and Lrig3.

LRIG1 modulates aggressiveness of head and neck cancers by regulating EGFR-MAPK-SPHK1 signaling and extracellular matrix remodeling

EGFR overexpression and chromosome 3p deletion are two frequent events in head and neck cancers. We previously mapped the smallest region of recurrent copy-number loss at 3p12.2-p14.1. LRIG1, a negative regulator of EGFR, was found at 3p14, and its copy-number loss correlated with poor clinical outcome. Inducible expression of LRIG1 in head and neck cancer TW01 cells, a line with low LRIG1 levels, suppressed cell proliferation in vitro and tumor growth in vivo. Gene expression profiling, quantitative RT-PCR, chromatin immunoprecipitation, and western blot analysis demonstrated that LRIG1 modulated extracellular matrix (ECM) remodeling and EGFR-MAPK-SPHK1 transduction pathway by suppressing expression of EGFR ligands/activators, MMPs and SPHK1. In addition, LRIG1 induction triggered cell morphology changes and integrin inactivation, which coupled with reduced SNAI2 expression. By contrast, knockdown of endogenous LRIG1 in TW06 cells, a line with normal LRIG1 levels, significantly enhanced cell proliferation, migration and invasiveness. Such tumor-promoting effects could be abolished by specific MAPK or SPHK1 inhibitors. Our data suggest LRIG1 as a tumor suppressor for head and neck cancers; LRIG1 downregulation in cancer cells enhances EGFR-MAPK-SPHK1 signaling and ECM remodeling activity, leading to malignant phenotypes of head and neck cancers.

A role for LRIG1 in the regulation of malignant glioma aggressiveness

The molecular mechanisms that drive the development and aggressive progression of malignant astrocytic tumors remain obscure. Recently, in the search for endogenous negative regulators of EGF receptor, LRIG1 was cloned and characterized as a putative tumor suppressor gene often downregulated in various human tumors, including astrocytic tumors. Although several studies have implicated the function of LRIG1 in the inhibition of tumorigenesis, its precise role and potential underlying mechanisms remain obscure. Therefore, we generated a full-length expression vector to overexpress LRIG1 in the U251 malignant glioma cell line. Introduction of exogenous LRIG1 into glioma cells inhibited cell proliferation manifested by MTT and soft agar clone assay in vitro and subcutaneously tumor xenografts. On the other hand, LRIG1 overexpression inhibited glioma growth by significantly changing the expression pattern of cyclins, resulting in delayed cell cycle. Employing transwell invasion and wound scratch assay and gelatin zymography, LRIG1 inhibited U-251 MG cell invasion and migration by attenuating MMP2 and MMP9 production. Under ligand-stimulated conditions, p-ERK levels did not change, whereas p-AKT levels were inhibited in cells with LRIG1 upregulation, indicating that LRIG1 exerts more inhibiting effects on the PI3K/AKT pathway. Our findings suggest that LRIG1 restricted glioma aggressiveness by inhibiting cell proliferation, migration and invasion. Restoration of LRIG1 to glioma cells could offer a novel therapeutic strategy.

Downregulation of LRIG1 expression by RNA interference promotes the aggressive properties of glioma cells via EGFR/Akt/c-Myc activation

The LRIG1 [leucine-rich repeats and immunoglobulin-like domains (LRIG)] gene is not universally downregulated in human cancers, and its role in tumorigenesis and the development of glioma has not been well addressed. In this study, we used short hairpin RNA (shRNA)-triggered RNA interference (RNAi) to block LRIG1 gene expression in the GL15 human glioma cell line. Specific downregulation of LRIG1 by shRNA resulted in significantly enhanced capabilities of proliferation, inhibition of apoptosis and invasion in the GL15 cells. LRIG1 repression induced marked activation of epidermal growth factor receptor (EGFR), protein kinase B (Akt) and c-Myc signaling molecules. Our results demonstrated that RNAi against LRIG1 may effectively downregulate LRIG1 gene expression. LRIG1 functions as a tumor suppressor in the pathogenesis of glioma via EGFR/Akt/c-Myc activation.

Gene expression pattern of the epidermal growth factor receptor family and LRIG1 in renal cell carcinoma

Background

Previous studies have revealed altered expression of epidermal growth factor receptor (EGFR)-family members and their endogenous inhibitor leucine-rich and immunoglobulin-like domains 1 (LRIG1) in renal cell carcinoma (RCC). In this study, we analyzed the gene expression levels of EGFR-family members and LRIG1, and their possible associations with clinical parameters in various types of RCC.

Methods

Gene expression levels of EGFR–family members and LRIG1 were analyzed in 104 RCC samples, including 81 clear cell RCC (ccRCC), 15 papillary RCC (pRCC), and 7 chromophobe RCC (chRCC) by quantitative real-time RT-PCR. Associations between gene expression levels and clinical data, including tumor grade, stage, and patient survival were statistically assessed.

Results

Compared to kidney cortex, EGFR was up-regulated in ccRCC and pRCC, LRIG1 and ERBB2 were down-regulated in ccRCC, and ERBB4 was strongly down-regulated in all RCC types. ERBB3 expression did not differ between RCC types or between RCC and the kidney cortex. The expression of the analyzed genes did not correlate with patient outcome.

Conclusions

This study revealed that the previously described up-regulation of EGFR and down-regulation of ERBB4 occurred in all analyzed RCC types, whereas down-regulation of ERBB2 and LRIG1 was only present in ccRCC. These observations illustrate the need to evaluate the different RCC types individually when analyzing molecules of interest and potential biological markers.

The pan-ErbB negative regulator Lrig1 is an intestinal stem cell marker that functions as a tumor suppressor

Lineage mapping has identified both proliferative and quiescent intestinal stem cells, but the molecular circuitry controlling stem cell quiescence is incompletely understood. By lineage mapping, we show Lrig1, a pan-ErbB inhibitor, marks predominately noncycling, long-lived stem cells that are located at the crypt base and that, upon injury, proliferate and divide to replenish damaged crypts. Transcriptome profiling of Lrig1(+) colonic stem cells differs markedly from the profiling of highly proliferative, Lgr5(+) colonic stem cells; genes upregulated in the Lrig1(+) population include those involved in cell cycle repression and response to oxidative damage. Loss of Apc in Lrig1(+) cells leads to intestinal adenomas, and genetic ablation of Lrig1 results in heightened ErbB1-3 expression and duodenal adenomas. These results shed light on the relationship between proliferative and quiescent intestinal stem cells and support a model in which intestinal stem cell quiescence is maintained by calibrated ErbB signaling with loss of a negative regulator predisposing to neoplasia.

Expression of EGFR and LRIG proteins in oesophageal carcinoma with emphasis on patient survival and cellular chemosensitivity

BACKGROUND

Leucine-rich and immunoglobulin-like domains 1-3 (LRIG1-3) proteins have been implicated in the regulation of EGFR signalling. In the present study, we investigated the clinical implications of the expression of EGFR and LRIG1-3 in oesophageal carcinoma, as well as the correlation between their expression levels and the chemosensitivity of oesophageal carcinoma cell lines.

PATIENTS AND METHODS

Tumours from 80 patients with oesophageal carcinoma were investigated for the expression of EGFR and LRIG proteins by immunohistochemistry. Oesophageal carcinoma cell lines were investigated for their expression of EGFR and LRIG1, 2, and 3 by quantitative real time RT-PCR and for their sensitivity to commonly used chemotherapeutics by a cytotoxicity assay.

RESULTS AND DISCUSSION

Based on a total score of intensity and expression rates, a trend towards survival difference was found for EGFR (p = 0.09) and LRIG2 (p = 0.18) whereas for LRIG1 and -3 there was no trend towards any association with survival. Correlation analysis revealed a correlation with the clinical expression of EGFR and LRIG3 (p = 0.0007). Significant correlations were found between LRIG1 expression levels and sensitivity to cisplatin (r = -0.74), docetaxel (r = -0.69), and vinorelbine (r = -0.82) in oesophageal carcinoma cell lines. EGFR and the LRIG proteins may be functionally involved in oesophageal carcinoma, but larger materials are needed to fully elucidate the clinical implication.

Lrig1 is an estrogen-regulated growth suppressor and correlates with longer relapse-free survival in ERα-positive breast cancer

Lrig1 is the founding member of the Lrig family and has been implicated in the negative regulation of several oncogenic receptor tyrosine kinases including ErbB2. Lrig1 is expressed at low levels in several cancer types but is overexpressed in some prostate and colorectal tumors. Given this heterogeneity, whether Lrig1 functions to suppress or promote tumor growth remains a critical question. Previously, we found that Lrig1 was poorly expressed in ErbB2-positive breast cancer, suggesting that Lrig1 has a growth-inhibitory role in this tumor type. However, breast cancer is a complex disease, with ErbB2-positive tumors accounting for just 25% of all breast cancers. To gain a better understanding of the role of Lrig1 in breast cancer, we examined its expression in estrogen receptor α (ERα)-positive disease which accounts for the majority of breast cancers. We find that Lrig1 is expressed at significantly higher levels in ERα-positive disease than in ERα-negative disease. Our study provides a molecular rationale for Lrig1 enrichment in ERα-positive disease by showing that Lrig1 is a target of ERα. Estrogen stimulates Lrig1 accumulation and disruption of this induction enhances estrogen-dependent tumor cell growth, suggesting that Lrig1 functions as an estrogen-regulated growth suppressor. In addition, we find that Lrig1 expression correlates with prolonged relapse-free survival in ERα-positive breast cancer, identifying Lrig1 as a new prognostic marker in this setting. Finally, we show that ErbB2 activation antagonizes ERα-driven Lrig1 expression, providing a mechanistic explanation for Lrig1 loss in ErbB2-positive breast cancer. This work provides strong evidence for a growth-inhibitory role for Lrig1 in breast cancer.

Regulation of epidermal growth factor receptor signalling by inducible feedback inhibitors

Signalling by the epidermal growth factor receptor (EGFR) controls morphogenesis and/or homeostasis of several tissues from worms to mammals. The correct execution of these programmes requires the generation of EGFR signals of appropriate strength and duration. This is obtained through a complex circuitry of positive and negative feedback regulation. Feedback inhibitory mechanisms restrain EGFR activity in time and space, which is key to ensuring that receptor outputs are commensurate to the cell and tissue needs. Here, we focus on the emerging field of inducible negative feedback regulation of the EGFR in mammals. In mammalian cells, four EGFR inducible feedback inhibitors (IFIs), namely LRIG1, RALT (also known as MIG6 and ERRFI1), SOCS4 and SOCS5, have been discovered recently. EGFR IFIs are expressed de novo in the context of early or delayed transcriptional responses triggered by EGFR activation. They all bind to the EGFR and suppress receptor signalling through several mechanisms, including catalytic inhibition and receptor downregulation. Here, we review the mechanistic basis of IFI signalling and rationalise the function of IFIs in light of gene-knockout studies that assign LRIG1 and RALT an essential role in restricting cell proliferation. Finally, we discuss how IFIs might participate in system control of EGFR signalling and highlight the emerging roles for IFIs in the suppression of EGFR-driven tumorigenesis.

Correlation between LRIG1 and LRIG2 expressions and expression of 11 tumor markers, with special reference to tumor suppressors, in CIN and normal cervical epithelium

OBJECTIVE

Novel biological markers LRIG1 and LRIG2 have been associated with favorable as well as poor prognosis, respectively, in different cancer types, including cervical cancer. The aim of this study was to investigate possible interactions between these proteins and other tumor markers, and as diagnostic adjuncts in CIN.

METHODS

Cervical biopsies from 171 women, with normal epithelium, and low-grade and high-grade CIN were stained for LRIG1 and LRIG2, and 11 additional tumor markers. The tumor markers were chosen to be relevant in cervical neoplasms. Staining was evaluated semiquantitatively.

RESULTS

Expression of LRIG1 and LRIG2 was found to correlate with increasing CIN grade, as well as with expression of tumor suppressor FHIT, independent of histological grade. In addition, tumor promoter LRIG2 expression correlated negatively with expression of tumor suppressor retinoblastoma protein and positively with IL-10. The latter correlation did not however remain after adjustment for CIN grade. p53 and p16 expressions correlated positively with LRIG1 expression in univariate analyses, but significance did not hold after adjustment for CIN grade.

CONCLUSION

LRIG1 and LRIG2 expressions were seen in precancerous cervical epithelium and found to increase with increasing grade. There was an association between expression of these glycoproteins and FHIT tumor suppressor protein, independently of histological grade.

LRIG1 and the liar paradox in prostate cancer: a study of the expression and clinical significance of LRIG1 in prostate cancer

The course of prostate cancer varies greatly, and additional prognostic markers are needed. Leucine-rich repeats and immunoglobulin-like domains protein 1 (LRIG1) is an endogenous inhibitor of growth factor signaling and a proposed tumor suppressor. Publicly available gene expression datasets indicate that LRIG1 may be overexpressed in prostate cancer. In our study, the expression of LRIG1 protein in prostate cancer was evaluated for the first time. Immunohistochemistry was performed on tissue microarrays from two different patient series: 355 Swedish patients diagnosed by transurethral resection and 293 American patients who underwent radical prostatectomy. In the Swedish series, high expression of LRIG1 correlated with Gleason score, T-stage, tumor cell proliferation, vascular density and epidermal growth factor receptor (EGFR) phosphorylation. Among the 256 Swedish patients, followed by watchful waiting, high LRIG1 expression was significantly associated with short overall and prostate cancer-specific survival. In contrast, in the US series, high LRIG1 expression was significantly associated with long overall survival. In vitro cell experiments showed that LRIG1 was induced by androgen stimulation, and its expression inhibited prostate cancer cell proliferation. Thus, LRIG1 expression was an independent marker for poor survival in the untreated patient series, perhaps as a secondary marker of androgen receptor and/or EGFR activation. On the contrary, LRIG1 was a marker for good prognosis after prostatectomy, which might be due to its growth inhibiting properties. We propose that LRIG1 is an important determinant of prostate cancer growth, and the implications of its expression on patient outcome depend on the clinical and biological circumstances.

Ex vivo assays of CEM cells cultured and treated in the three dimensional cultures

This study was aimed at the applications of an ex vivo assays to characterization of CEM (Human T-Lymphoblastoid) cells. CEM cells were cultured in three dimensional (3-D) geometry in the Hollow Fibre Bioreactor (HFB) device. The cells were treated with Herceptin, anti-HER-2 (clone CB-11) and lipoplex containing lipofectamine (LipA) and plasmid DNA. To identify the response to treatment, the viability was established using Trypan blue assays. Magnetic resonance imaging (MRI) at 9.4Tesla (T) was applied for localization of the cells in the HFB device. The structural changes in the cells associated with treatment were examined with matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS). The tryptic peptides and glycopeptides detected in treated cells provided evidence of the efficacy of antibody binding to the receptor. The results of the study confirmed that cells growth significantly decreased after treatment with antibodies and transfection with lipoplex.

Functional genomics and proteomics approaches to study the ERBB network in cancer

Substantial progress in functional genomic and proteomic technologies has opened new perspectives in biomedical research. The sequence of the human genome has been mostly determined and opened new visions on its complexity and regulation. New technologies, like RNAi and protein arrays, allow gathering knowledge beyond single gene analysis. Increasingly, biological processes are studied with systems biological approaches, where qualitative and quantitative data of the components are utilized to model the respective processes, to predict effects of perturbations, and to then refine these models after experimental testing. Here, we describe the potential of applying functional genomics and proteomics, taking the ERBB family of growth-factor receptors as an example to study the signaling network and its impact on cancer.

Upregulation of LRIG1 suppresses malignant glioma cell growth by attenuating EGFR activity

Activated epidermal growth factor receptor (EGFR) has emerged as an important therapeutic target for a variety of solid tumors, particularly malignant gliomas. A recently discovered transmembrane glycoprotein, LRIG1, antagonizes the activity of epidermal growth factor receptor family receptor tyrosine kinases and acts as a negative feedback loop of EGFR and proposed tumor suppressors. The aim of this study was to investigate the impact of LRIG1 on the biological features of glioma cells and the possible mechanisms of enhanced apoptosis induced by upregulation of LRIG1. We observed that the expression of LRIG1 was decreased, while the expression of EGFR was increased in the majority of astrocytomas, and the ratio of EGFR/LRIG1 was increased by sixfold in tumors versus corresponding non-neoplastic tissue. Upregulation of LRIG1, followed by a decrease of EGFR on the cytomembrane of the cells, induced cell apoptosis and cell growth inhibition, and further reversed invasion in glioma cell lines and primary glioma cells. Our study now clearly indicates that LRIG1 indeed affects cell fate and biology behaviors of the cells in vitro by inhibiting phosphorylation of downstream MAPK and AKT signaling pathway, and the elevated release level of caspase-8 might contribute to the enhanced apoptosis in LRIG1 transfected glioma cells. Taken together, these findings provide us with an insight into LRIG1 function, and we conclude that LRIG1 evolved in gliomas as a rare feedback negative attenuator of EGFR and could offer a novel therapeutic target to treat patients with malignant gliomas.

Suppression of the negative regulator LRIG1 contributes to ErbB2 overexpression in breast cancer

The ErbB2 receptor tyrosine kinase is overexpressed in approximately 25% of breast tumors and contributes to poor patient prognosis and therapeutic resistance. Here, we examine the role of the recently discovered ErbB negative regulator LRIG1 in ErbB2(+) breast cancer. We observe that LRIG1 protein levels are significantly suppressed in ErbB2-induced mammary tumors in transgenic mice as well as in the majority of ErbB2(+) human breast tumors. These observations raise the possibility that LRIG1 loss could contribute to the initiation or growth of ErbB2(+) breast tumors. RNA interference-mediated knockdown of endogenous LRIG1 in the ErbB2-overexpressing breast tumor cell lines MDA-MB-453 and BT474 further elevates ErbB2 in these cells and augments cellular proliferation. In contrast, ectopic expression of LRIG1 reverses these trends. Interestingly, we observe that LRIG1 protein levels are suppressed in response to ErbB receptor activation in breast tumor cells but are unaffected by ErbB activation in immortalized nontransformed breast epithelial cells. Our observations indicate that the suppression of LRIG1 protein levels is a common feature of breast tumors. Moreover, our observations point to the existence of a feed-forward regulatory loop in breast tumor cells where aberrant ErbB2 signaling suppresses LRIG1 protein levels, which in turn contributes to ErbB2 overexpression.

Down-regulation of leucine-rich repeats and immunoglobulin-like domain proteins (LRIG1-3) in HP75 pituitary adenoma cell line

Three human leucine-rich repeats and immunoglobulin-like domains (LRIG) genes and proteins, named LRIG1-3, has been previously characterized and it was proposed that they may act as suppressors of tumor growth. The LRIG1 protein can inhibit the growth of tumors of glial cells and the down-regulation of the LRIG1 gene may be involved in the development and progression of the tumor. Real-time reverse transcription-polymerase chain reaction (RT-PCR) is a recently developed technique for quantitative assessment of specific RNA levels. In the current study, it was demonstrated that LRIG1-3 and EGFR mRNA was detected in human pituitary adenoma cell lines and a normal pituitary sample, with differences in the expression levels. Compared to the normal pituitary samples, the expression of LRIG1-3 in HP75 cell line was lower, but the expression of EGFR in HP75 cell line was higher. The results are consistent with LRIG1-3 being tumour suppressor genes, and LRIG genes decreasing the expression of EGFR. The ratio of EGFR/LRIG1 was increased at least 13-fold in HP75 cells compared with the normal pituitary cells, which was also the case for the ratio of EGFR/LRIG2 (14-fold increase in HP75) and EGFR/LRIG3 (11-fold increase in HP75). Further studies were needed to elucidate the explicit role of LRIG genes as negative regulators of oncogenesis in human pituitary adenoma.

LRIG1 negatively regulates the oncogenic EGF receptor mutant EGFRvIII

Epidermal growth factor receptor (EGFR) mutation is frequently observed in human cancer and contributes to the growth, survival and therapeutic resistance of tumors. EGFRvIII is an oncogenic EGFR mutant resulting from the deletion of exons 2-7 and is the most common EGFR mutant observed in glioblastoma multiforme, an aggressive brain tumor. EGFRvIII is constitutively active but poorly ubiquitinated, leading to inefficient receptor trafficking to lysosomes and unattenuated oncogenic signaling. The mechanism by which EGFRvIII evades downregulation is not fully understood although recent studies suggest that its interaction with the ubiquitin ligase Cbl may be compromised. In this study, we examine the regulation of EGFRvIII by the recently identified negative regulator, LRIG1, which targets EGFR through recognition of its extracellular domain. Here, we determine whether the extracellular domain deletion in EGFRvIII renders it refractory to LRIG1 regulation. We find that EGFRvIII retains interaction with LRIG1 and is in fact more sensitive to LRIG1 action than wild-type receptor. We demonstrate that LRIG1 regulation of EGFRvIII is distinct from the only other known mechanism of EGFR regulation, Cbl-mediated degradation. Ectopic expression of LRIG1 in EGFRvIII(+) glioblastoma cells opposes EGFRvIII-driven tumor cell proliferation, survival, motility and invasion. Finally, RNAi-mediated silencing of LRIG1 alters EGFRvIII intracellular trafficking and leads to enhanced EGFRvIII expression, suggesting that loss of LRIG1 in tumors may contribute to a permissive environment for EGFRvIII overexpression, contributing to EGFRvIII oncogenesis.

Von Hippel-Lindau tumor suppressor gene loss in renal cell carcinoma promotes oncogenic epidermal growth factor receptor signaling via Akt-1 and MEK-1

OBJECTIVES

Clear-cell renal cell carcinoma (RCC) is the most prevalent form of kidney cancer and is frequently associated with loss of von Hippel-Lindau (VHL) gene function, resulting in the aberrant transcriptional activation of genes that contribute to tumor growth and metastasis, including transforming growth factor-alpha (TGF-alpha), a ligand of the epidermal growth factor receptor (EGFR) tyrosine kinase. To determine the functional impact of EGFR activation on RCC, we suppressed critical components of this pathway: EGFR, Akt-1, and MEK-1.

METHODS

Stable transfection of RCC cells with plasmids bearing shRNA directed against each of these genes was used to individually suppress their expression. Transfectants were characterized for growth and invasiveness in vitro and tumorigenesis in vivo.

RESULTS

RCC cell transfectants displayed significantly reduced growth rate and matrix invasion in vitro and RCC tumor xenograft growth rate in vivo. Analysis of tumor cells that emerged after extended periods in each model showed that significant EGFR suppression was sustained, whereas Akt-1 and MEK-1 knock-down cells had escaped shRNA suppression.

CONCLUSIONS

EGFR, Akt-1, and MEK-1 are individually critical for RCC cell invasiveness in vitro and tumorigenicity in vivo, and even partial suppression of each can have a significant impact on tumor progression. The emergence of transfectants that had escaped Akt-1 and MEK-1 suppression during tumorigenicity experiments suggests that these effectors may each be more critical than EGFR for RCC tumorigenesis, consistent with results from clinical trials of EGFR inhibitors for RCC, where durable clinical responses have not been seen.

LRIG1 and squamous epithelial uterine cervical cancer: correlation to prognosis, other tumor markers, sex steroid hormones, and smoking

The aim is to evaluate LRIG1 as a prognosis predictor and correlations to cofactors in squamous cell cervical cancer. LRIG1 expression was studied in 128 cervical carcinomas and was compared with expression of nine other tumor markers. Smoking history was registered and pretreatment serum estradiol and progesterone levels were evaluated in 79 women. At clinical stage IB, 58% of the tumors showed LRIG1 expression, but there was a decline by increasing stage (33% in stage IV). Ninety percent of women with stage IB cancer and LRIG1 positivity survived, as compared to 64% without expression (P = 0.02). LRIG1 expression did not predict prognosis in advanced stages, but in stage IIA there was a marked relative difference, with 75% survival in tumors expressing LRIG1, as compared to 43% in those without. No correlation was found between LRIG1 and the other nine tumor markers studied. A high serum progesterone and smoking correlated to absent LRIG1 expression. We conclude that LRIG1 appears to be a significant prognosis predictor in early-stage cervical cancer, independent of the other tumor markers that were studied. Diminished expression in advanced stages and the inverse correlation to serum progesterone and smoking indicates that LRIG1 is a tumor suppressor in cervix.

The Prognostic Significance of Epidermal Growth Factor Receptor Expressionin Clear-Cell Renal Cell Carcinoma: A Call for Standardized Methods for Immunohistochemical Evaluation

BACKGROUND

Epidermal growth factor receptor (EGFR) is overexpressed in the majority of clear-cell renal cell carcinomas (RCCs). The prognostic significance of EGFR overexpression after nephrectomy, however, is controversial because of different methods used in the immunohistochemical (IHC) evaluation of EGFR expression.

PATIENTS AND METHODS

In this study, we evaluated EGFR expression and its prognostic significance using 3 IHC evaluation methods. A tissue microarray composed of 44 cases of clear-cell RCC was stained for the patterns of EGFR overexpression, including membranous, cytoplasmic (EGFR-c), and total (membranous and cytoplasmic), and the percentage of cells positive for EGFR overexpression were recorded. An EGFR composite score was calculated by multiplying the total EGFR overexpression score (0-3) and percentage of positive cells.

RESULTS

Membranous EGFR overexpression was detected in 38 of 44 cases (93.2%), with moderate to strong staining (scores 2 and 3) in 35 cases (79.5%). EGFR-c was detected in 28 cases (63.6%), with moderate to strong staining (scores 2 and 3) in 16 cases (36.4%). EGFR-c was significantly associated with pathologic stage (P = 0.003) and Fuhrman nuclear grade (P = 0.042). Epidermal growth factor receptor composite score correlated with pathologic stage (P = 0.045) but not Fuhrman nuclear grade. However, EGFR expression did not correlate with overall survival or disease recurrence.

CONCLUSION

This study demonstrates that the prognostic value of EGFR overexpression differs significantly when different methods are used to evaluate EGFR expression by IHC. Future studies should use standardized methods to evaluate the EGFR staining pattern and intensity and the percentage of positive cells in order to clarify the prognostic significance of EGFR overexpression in clear-cell RCC.

Negative Regulation of Receptor Tyrosine Kinase (RTK) Signaling: A Developing Field

Trophic factors control cellular physiology by activating specific receptor tyrosine kinases (RTKs). While the over activation of RTK signaling pathways is associated with cell growth and cancer, recent findings support the concept that impaired down-regulation or deactivation of RTKs may also be a mechanism involved in tumor formation. Under this perspective, the molecular determinants of RTK signaling inhibition may act as tumor-suppressor genes and have a potential role as tumor markers to monitor and predict disease progression. Here, we review the current understanding of the physiological mechanisms that attenuate RTK signaling and discuss evidence that implicates deregulation of these events in cancer.

LRIG inhibitors of growth factor signalling - double-edged swords in human cancer?

The leucine-rich repeats and immunoglobulin-like domains (LRIG) proteins are newly discovered negative regulators of growth factor signalling and proposed tumour suppressors. They antagonise signalling by interacting with growth factor receptors and by enhancing their ubiquitylation and degradation. Data on the expression of LRIG in human cancer have recently begun to accumulate; however, not all data appear consistent with the notion that the LRIG proteins always function as tumour suppressors. In the present review, we argue that the LRIG proteins could be double-edged swords, promoting or suppressing human cancer depending on cellular context.

LRIG1 is a novel negative regulator of the Met receptor and opposes Met and Her2 synergy

The Met receptor tyrosine kinase regulates a complex array of cellular behaviors collectively known as "invasive growth." While essential for normal development and wound repair, this program is frequently co-opted by tumors to promote their own growth, motility, and invasion. Met is overexpressed in a variety of human tumors, and this aberrant expression correlates with poor patient prognosis. Previous studies indicate that Met receptor levels are governed in part by cbl-mediated ubiquitination and degradation, and uncoupling of Met from cbl-mediated ubiquitination promotes its transforming activity. Here we describe a novel mechanism for Met degradation. We find that the Met receptor interacts with the transmembrane protein LRIG1 independent of hepatocyte growth factor (HGF) stimulation and that LRIG1 destabilizes the Met receptor in a cbl-independent manner. Overexpression of LRIG1 destabilizes endogenous Met receptor in breast cancer cells and impairs their ability to respond to HGF. LRIG1 knockdown increases Met receptor half-life, indicating that it plays an essential role in Met degradation. Finally, LRIG1 opposes Met synergy with the ErbB2/Her2 receptor tyrosine kinase in driving cellular invasion. We conclude that LRIG1 is a novel suppressor of Met function, serving to regulate cellular receptor levels by promoting Met degradation in a ligand- and cbl-independent manner.

LRIG1, a candidate tumour-suppressor gene in human bladder cancer cell line BIU87

OBJECTIVES

To determine the effects of LRIG1 on the growth, migration and invasion of bladder cancer cells and the mechanisms underlying such effects.

MATERIALS AND METHODS

The plasmid pLRIG1-green fluorescence protein (GFP) was transfected into BIU87 bladder cancer cells by Lipofectamine2000 (Invitrogen, Groningen, the Netherlands), and the cells that expressed LRIG1 stably were screened out by G418. The changes in LRIG1 and epidermal growth factor receptor (EGFR) protein levels were measured by Western blot; growth curves were estimated by the tetrazolium (MTT) assay; then cell-cell adhesion, cell-matrix adhesion and cell invasion assays were used to measure proliferation, adhesion and invasion in LGIR1-transfected and control cells.

RESULTS

The LRIG1 protein level in pLRIG1-GFP transfected cells was significantly higher than that in control cells, while the EGFR protein level was significantly lower. pLRIG1-GFP transfected cells had less proliferation than control cells. Contrasting with non-LRIG1-transfected cells, the invasion and cell-matrix adhesion ability of pLRIG1-GFP transfected cells decreased markedly, and conversely the homotypic cell-cell adhesion ability was significantly higher.

CONCLUSIONS

LRIG1 might act as a tumour-suppressor gene, participating in negative feedback control of EGFR expression, which inhibits bladder cancer cells from growth, migration and invasion.

A soluble ectodomain of LRIG1 inhibits cancer cell growth by attenuating basal and ligand-dependent EGFR activity

Leucine-rich repeats and immunoglobulin-like domains-1 (LRIG1) is a transmembrane protein with an ectodomain containing 15 leucine-rich repeats (LRRs) homologous to mammalian decorin and the Drosophila kekkon1 gene. In this study, we demonstrate that a soluble ectodomain of LRIG1, containing only the LRRs, inhibits ligand-independent epidermal growth factor receptor (EGFR) activation and causes growth inhibition of A431, HeLa and MDA-468 carcinoma cells. In contrast, cells that do not express detectable levels of EGFR fail to respond to soluble LRIG1. However, when a functional EGFR gene is introduced in these cells, they become growth-inhibited by soluble LRIG1 protein. Furthermore, we demonstrate the existence of high-affinity (K(d)=10 nM) binding sites on the A431 cells that can be competitively displaced (up to 75%) by molar excess of EGF. Even more powerful effects are obtained with a chimeric proteoglycan harboring the N-terminus of decorin, substituted with a single glycosaminoglycan chain, fused to the LRIG1 ectodomain. Both proteins also inhibit ligand-dependent activation of the EGFR and extracellular signal-regulated protein kinase 1/2 signaling in a rapid and dose-dependent manner. These results suggest a novel mechanism of action evoked by a soluble ectodomain of LRIG1 protein that could modulate EGFR signaling and its growth-promoting activity. Attenuation of EGFR activity without physical downregulation of the receptor could represent a novel therapeutic approach toward malignancies in which EGFR plays a primary role in tumor growth and survival.

Perinuclear leucine-rich repeats and immunoglobulin-like domain proteins (LRIG1-3) as prognostic indicators in astrocytic tumors

We have previously characterized three human leucine-rich repeats and immunoglobulin-like domains (LRIG) genes and proteins, named LRIG1-3 and proposed that they may act as suppressors of tumor growth. The LRIG1 transmembrane protein antagonizes the activity of epidermal growth factor receptor family receptor tyrosine kinases. In this study, we evaluated the mRNA expression level of LRIG1-3 in human glioma cell lines and control-matched glioma tissues, characterized the sub-cellular localization of an LRIG3-GFP fusion protein, and analyzed the relationship between sub-cellular localization of LRIG1-3 and clinical parameters in 404 astrocytic tumors by immunohistochemistry. LRIG1-3 mRNA was detected in all human glioma cell lines and matched glioma samples, with large differences in the expression levels. Ectopically expressed LRIG3-GFP localized to perinuclear and cytoplasmic compartments, and to the cell surface of transfected glioma cells. Perinuclear staining of LRIG1-3 was associated with low WHO grade and better survival of the patients. Perinuclear staining of LRIG3 was associated with a lower proliferation index and was in addition to tumor grade, an independent prognostic factor. Furthermore, within the groups of grade III and grade IV tumors, perinuclear staining of LRIG3 significantly correlated with better survival. These results indicate that expression and sub-cellular localization of LRIG1-3 might be of importance in the pathogenesis and prognosis of astrocytic tumors.

ErbB receptor negative regulatory mechanisms: implications in cancer

Activation of ErbB receptor tyrosine kinases (RTKs) must be precisely regulated to ensure the fidelity of developmental and homeostatic processes mediated by growth factors. Insufficient receptor stimulation will lead to defects in tissue development, while excessive stimulation can lead to hyperplastic events associated with cancer and other diseases. A coordinated balance of the intensity and timing of receptor signaling, achieved through both receptor activation and negative regulatory mechanisms, is required for signaling fidelity. While considerable effort has gone into understanding mechanisms by which ErbB receptors are activated, our understanding of the suppression of growth factor receptor activity remains limited. While ligand-stimulated receptor degradation is the most thoroughly examined mechanism for preventing hyper-signaling by ErbBs, recent studies indicate that several other mechanisms act directly on receptors to suppress receptor levels, or the magnitude or duration of receptor signaling. ErbB receptor overexpression or aberrant activation contributes to the progression of numerous solid tumor types. Hence, tumor cells must overcome these endogenous receptor negative regulatory mechanisms before they can exploit ErbB receptors to achieve uncontrolled growth. Here we will discuss several proteins that directly interact with ErbB receptors to suppress signaling, highlighting the potential impact of their loss on tumor progression.

Increased copy number at 3p14 in breast cancer

INTRODUCTION

The present study was conducted to investigate if chromosome band 3p14 is of any pathogenic significance in the malignant process of breast cancer. Genetic studies have implicated a tumour suppressor gene on chromosome arm 3p and we have proposed LRIG1 at 3p14 as a candidate tumour suppressor. The LRIG1 gene encodes an integral membrane protein that counteracts signalling by receptor tyrosine kinases belonging to the ERBB family. LRIG1 mRNA and protein are expressed in many tissues, including breast tissue.

METHODS

In the present report we analysed the LRIG1 gene by fluorescence in situ hybridisation (FISH), LRIG1 mRNA by quantitative RT-PCR, and LRIG1 protein by western blot analysis. Two tumour series were analysed; one series consisted of 19 tumour samples collected between 1987 and 1995 and the other series consisted of 9 tumour samples with corresponding non-neoplastic breast tissues collected consecutively.

RESULTS

The LRIG1 gene showed increased copy number in 11 out of 28 tumours (39%) and only one tumour showed a deletion at this locus. Increased LRIG1 copy number was associated with increased levels of LRIG1 mRNA (two of three tumours) and protein (four of four tumours) in the tumours compared to matched non-neoplastic breast tissue, as assessed by RT-PCR and western blot analysis.

CONCLUSION

The molecular function of LRIG1 as a negative regulator of ERBB receptors questions the biological significance of increased LRIG1 copy number in breast cancer. We propose that a common, but hitherto unrecognised, breast cancer linked gene is located within an amplicon containing the LRIG1 locus at 3p14.3.