The Role of IgLON Cell Adhesion Molecules in Neurodegenerative Diseases

In the brain, cell adhesion molecules (CAMs) are critical for neurite outgrowth, axonal fasciculation, neuronal survival and migration, and synapse formation and maintenance. Among CAMs, the IgLON family comprises five members: Opioid Binding Protein/Cell Adhesion Molecule Like (OPCML or OBCAM), Limbic System Associated Membrane Protein (LSAMP), neurotrimin (NTM), Neuronal Growth Regulator 1 (NEGR1), and IgLON5. IgLONs exhibit three N-terminal C2 immunoglobulin domains; several glycosylation sites; and a glycosylphosphatidylinositol anchoring to the membrane. Interactions as homo- or heterodimers in cis and in trans, as well as binding to other molecules, appear critical for their functions. Shedding by metalloproteases generates soluble factors interacting with cellular receptors and activating signal transduction. The aim of this review was to analyse the available data implicating a role for IgLONs in neuropsychiatric disorders. Starting from the identification of a pathological role for antibodies against IgLON5 in an autoimmune neurodegenerative disease with a poorly understood mechanism of action, accumulating evidence links IgLONs to neuropsychiatric disorders, albeit with still undefined mechanisms which will require future thorough investigations.

Bioinformatics analysis and experimental validation identified HMGA2/microRNA-200c-3p/LSAMP/Wnt axis as an immunological factor of patients with colorectal cancer

Colorectal cancer (CRC) is one of the most common malignant cancers. The tumor microenvironment (TME) plays an important role in tumor progression and affects the prognosis of CRC patients. However, the TME has been poorly characterized and studies aiming to identify the biomarkers or combined risk scores of CRC patients are limited. Here, we overlapped differentially expressed genes and stromal/immune-score-related modules to identify immune- and stromal-related genes in CRC patients. These genes were fed into the LASSO-Cox regression analysis for dimensionality reduction to establish a TME-associated risk model. A high TME-associated risk score was identified as an unfavorable prognostic factor in The Cancer Genome Atlas and Gene Expression Omnibus datasets, as well as in a subgroup analysis, stratified by gender, age, microsatellite instability, and tumor lymph node metastasis stage. Ten genes were mutated more frequently in the high TME-associated risk score group; these mutations may be related to changes in the TME and the response to immunotherapy. Thus, a lower TME-associated risk score may indicate a better response to immunotherapy and longer overall survival. Experimental validation demonstrated that LSAMP, a novel TME-associated-risk-score-related gene, increased sensitivity of CRC to CD8+-T-cell-mediated cytotoxicity. A mechanistic investigation showed that the HMGA2/microRNA-200c-3p/LSAMP/Wnt axis was an immunological factor in CRC patients. To conclusion, we demonstrated that the TME-associated risk score model could be a reliable prognostic biomarker for CRC patients and highlighted the significance of the HMGA2/microRNA-200c-3p/LSAMP/Wnt axis in the oncoimmunology of CRC.

The Downregulation of LSAMP Expression Promotes Lung Cancer Progression and Is Associated with Poor Survival Prognosis

Lung cancer has been a leading cause of cancer-related death for decades and therapeutic strategies for non-driver mutation lung cancer are still lacking. A novel approach for this type of lung cancer is an emergent requirement. Here we find that loss of LSAMP (Limbic System Associated Membrane Protein), compared to other IgLON family of proteins NTM (Neurotrimin) and OPCML (OPioid-binding Cell adhesion MoLecule), exhibits the strongest prognostic and therapeutic significance in predicting lung adenocarcinoma (LUAD) progression. Lower expression of LSAMP and NTM, but not OPCML, were found in tumor parts compared with normal parts in six LUAD patients, and this was validated by public datasets, Oncomine^® and TCGA. The lower expression of LSAMP, but not NTM, was correlated to shorter overall survival. Two epigenetic regulations, including hypermethylation and miR-143-3p upregulation but not copy number variation, were associated with downregulation of LSAMP in LUAD patients. Pathway network analysis showed that NEGR1 (Neuronal Growth Regulator 1) was involved in the regulatory loop of LSAMP. The biologic functions by LSMAP knockdown in lung cancer cells revealed LSMAP was linked to cancer cell migration via epithelial-mesenchymal transition (EMT) but not proliferation nor stemness of LUAD. Our result showed for the first time that LSAMP acts as a potential tumor suppressor in regulating lung cancer. A further deep investigation into the role of LSAMP in lung cancer tumorigenesis would provide therapeutic hope for such affected patients.

Amalgam regulates the receptor tyrosine kinase pathway through Sprouty in glial cell development in the Drosophila larval brain

The receptor tyrosine kinase (RTK) pathway plays an essential role in development and disease by controlling cell proliferation and differentiation. Here, we profile the Drosophila larval brain by single-cell RNA-sequencing and identify Amalgam (Ama), which encodes a cell adhesion protein of the immunoglobulin IgLON family, as regulating the RTK pathway activity during glial cell development. Depletion of Ama reduces cell proliferation, affects glial cell type composition and disrupts the blood-brain barrier (BBB), which leads to hemocyte infiltration and neuronal death. We show that Ama depletion lowers RTK activity by upregulating Sprouty (Sty), a negative regulator of the RTK pathway. Knockdown of Ama blocks oncogenic RTK signaling activation in the Drosophila glioma model and halts malignant transformation. Finally, knockdown of a human ortholog of Ama, LSAMP, results in upregulation of SPROUTY2 in glioblastoma cell lines, suggesting that the relationship between Ama and Sty is conserved.

Promoter-Specific Expression and Genomic Structure of IgLON Family Genes in Mouse

IgLON family is composed of five genes: Lsamp, Ntm, Opcml, Negr1, and Iglon5; encoding for five highly homologous neural adhesion proteins that regulate neurite outgrowth and synapse formation. In the current study we performed in silico analysis revealing that Ntm and Opcml display similar genomic structure as previously reported for Lsamp, characterized by two alternative promotors 1a and 1b. Negr1 and Iglon5 transcripts have uniform 5′ region, suggesting single promoter. Iglon5, the recently characterized family member, shares high level of conservation and structural qualities characteristic to IgLON family such as N-terminal signal peptide, three Ig domains, and GPI anchor binding site. By using custom 5′-isoform-specific TaqMan gene-expression assay, we demonstrated heterogeneous expression of IgLON transcripts in different areas of mouse brain and several-fold lower expression in selected tissues outside central nervous system. As an example, the expression of IgLON transcripts in urogenital and reproductive system is in line with repeated reports of urogenital tumors accompanied by mutations in IgLON genes. Considering the high levels of intra-family homology shared by IgLONs, we investigated potential compensatory effects at the level of IgLON isoforms in the brains of mice deficient of one or two family members. We found that the lack of IgLONs is not compensated by a systematic quantitative increase of the other family members. On the contrary, the expression of Ntm 1a transcript and NEGR1 protein was significantly reduced in the frontal cortex of Lsamp-deficient mice suggesting that the expression patterns within IgLON family are balanced coherently. The actions of individual IgLONs, however, can be antagonistic as demonstrated by differential expression of Syp in deletion mutants of IgLONs. In conclusion, we show that the genomic twin-promoter structure has impact on both anatomical distribution and intra-family interactions of IgLON family members. Remarkable variety in the activity levels of 1a and 1b promoters both in the brain and in other tissues, suggests complex functional regulation of IgLONs by alternative signal peptides driven by 1a and 1b promoters.

A novel genomic alteration of LSAMP associates with aggressive prostate cancer in African American men

Evaluation of cancer genomes in global context is of great interest in light of changing ethnic distribution of the world population. We focused our study on men of African ancestry because of their disproportionately higher rate of prostate cancer (CaP) incidence and mortality. We present a systematic whole genome analyses, revealing alterations that differentiate African American (AA) and Caucasian American (CA) CaP genomes. We discovered a recurrent deletion on chromosome 3q13.31 centering on the LSAMP locus that was prevalent in tumors from AA men (cumulative analyses of 435 patients: whole genome sequence, 14; FISH evaluations, 101; and SNP array, 320 patients). Notably, carriers of this deletion experienced more rapid disease progression. In contrast, PTEN and ERG common driver alterations in CaP were significantly lower in AA prostate tumors compared to prostate tumors from CA. Moreover, the frequency of inter-chromosomal rearrangements was significantly higher in AA than CA tumors. These findings reveal differentially distributed somatic mutations in CaP across ancestral groups, which have implications for precision medicine strategies.

Overexpression of the LSAMP and TUSC7 genes in acute myeloid leukemia following microdeletion/duplication of chromosome 3

The 3q13.31 microdeletion syndrome is characterized by developmental delay, postnatal growth above the mean, characteristic facial features, and abnormal male genitalia. Moreover, a frequent deletion in the 3q13.31 chromosome region has been identified in patients who are affected by osteosarcomas. Among the genes located within the deleted region, the involvement of the limbic system-associated membrane protein gene (LSAMP), together with a non-coding RNA tumor suppressor candidate 7 gene (TUSC7), has been suggested. We describe the case of an adult acute myeloid leukemia (AML) patient with a novel chromosomal rearrangement characterized by a 3q13.31 microdeletion and an extra copy of the 3q13.31-q29 chromosomal region translocated to the long arm of the Y chromosome. This karyotypic aberration seems to cause LSAMP and TUSC7 gene expression dysregulation. In conclusion, we report the first case of LSAMP and TUSC7 gene overexpression, possibly due to a position effect in an AML patient bearing a 3q13.31 cryptic deletion.

Intratumoral heterogeneity of genomic imbalance in a case of epithelioid glioblastoma with BRAF V600E mutation

Epithelioid glioblastoma is among the rarest variants of glioblastoma and is not formally recognized in the World Health Organization classification; it is composed of monotonous, discohesive sheets of small, round cells with eccentric nuclei and eosinophilic cytoplasm devoid of cytoplasmic stellate processes, showing the retention of nuclear staining of INI-1 protein. Here, we report a case involving a 22-year-old man with a right occipital lobe tumor, which comprised mainly epithelioid tumor cells with a small area of diffusely infiltrating less atypical astrocytoma cells showing a lower cell density. Array comparative genomic hybridization separately performed for each histologically distinct component demonstrated eight shared copy number alterations (CNAs) and three CNAs observed only in epithelioid cells; one of the latter was a homozygous deletion of a tumor suppressor gene, LSAMP, at 3q13.31. BRAF V600E mutation was observed both in epithelioid tumor cells and in diffusely infiltrating less atypical astrocytoma cells. Our findings suggest that the regional loss of LSAMP led to the aggressive nature of epithelioid cells in the present case of epithelioid glioblastoma.