Alternative titles; symbols
HGNC Approved Gene Symbol: HEPACAM
Cytogenetic location: 11q24.2 Genomic coordinates (GRCh38) : 11:124,919,205-124,936,047 (from NCBI)
| Location | Phenotype |
Phenotype MIM number |
Inheritance |
Phenotype mapping key |
|---|---|---|---|---|
| 11q24.2 | Megalencephalic leukoencephalopathy with subcortical cysts 2A | 613925 | Autosomal recessive | 3 |
| Megalencephalic leukoencephalopathy with subcortical cysts 2B, remitting, with or without impaired intellectual development | 613926 | Autosomal dominant | 3 |
HEPACAM is a cell adhesion molecule of the immunoglobulin (Ig) family (Sirisi et al., 2014).
By database searching with the sequence of HEPN1 (611641) as query, Moh et al. (2005) identified a novel gene, designated HEPACAM, that contains the full-length HEPN1 on its antisense strand in the 3-prime noncoding region. A HEPACAM cDNA, isolated from liver, encodes a deduced 416-amino acid protein with the typical structure of Ig-like adhesion molecules, including 2 extracellular Ig-like domains, a transmembrane segment, and a cytoplasmic tail containing putative SH3 binding sites and potential serine/threonine and tyrosine kinase phosphorylation sites. RT-PCR demonstrated expression of HEPACAM in normal liver tissues, downregulated expression in hepatocellular carcinoma (HCC) tissues, and undetectable expression in HCC cell lines. Western blot analysis demonstrated that HEPACAM is glycosylated. A polyclonal antibody raised against the cytoplasmic domain of HEPACAM indicated that this domain is phosphorylated. Moh et al. (2005) suggested that HEPACAM may be a tumor suppressor in HCC.
From a human brain cDNA library, Favre-Kontula et al. (2008) isolated a clone corresponding to HEPACAM, which they called glial cell adhesion molecule (GlialCAM). The protein was predominantly expressed in the mouse and human nervous system. Expression in the liver was very low in humans, and liver expression was absent in mice. Detailed studies in mice showed expression of GlialCAM in ependymal cells of the brain ventricular zones and the central canal of the spinal cord, with predominant expression in glial cells. GlialCAM was upregulated in postnatal mouse brain development and showed concomitant expression with myelin basic protein (MBP; 159430). In vitro, GlialCAM was observed at various developmental stages of oligodendrocytes and in astrocytic processes and at cell contact sites.
Lopez-Hernandez et al. (2011) preferred the name GlialCAM above HEPACAM and noted that the protein is predominantly expressed in the central nervous system and that mutation in the gene results in a neurologic phenotype without sign of liver involvement.
By genomic sequence analysis, Moh et al. (2005) mapped the HEPACAM gene to chromosome 11q24.
Moh et al. (2005) demonstrated that the HEPACAM gene contains 7 exons ranging in size from 71 to 2,252 basepairs.
Moh et al. (2005) evaluated the cytoplasmic domain of HEPACAM by transfecting wildtype and cytoplasmic domain-truncated constructs of HEPACAM into breast carcinoma MCF7 cells and analyzing their effects on HEPACAM function. Biochemical analysis revealed that HEPACAM is a glycosylated protein that forms a cis-homodimer on the cell surface. Deletion of the cytoplasmic domain did not interfere with dimer formation, suggesting that this domain is not required for dimerization. Subcellular localization of HEPACAM in nonpolarized MCF7 cells showed that HEPACAM molecules were recruited to the cytoplasmic membranes at sites of cell-cell attachment. In polarized cells, HEPACAM was preferentially expressed in the lateral and basal membranes. Colocalization analysis demonstrated that HEPACAM colocalized laterally with E-cadherin (192090), but no direct contact between the 2 molecules was detected. Partial truncation and complete deletion of the cytoplasmic domain did not alter the plasma membrane location. Moh et al. (2005) found that HEPACAM is capable of modulating cell-matrix interaction and of mediating substrate affinity and cell motility. Deletion of the cytoplasmic domain reduced, but did not completely abrogate, cell-matrix adhesion, but was essential for wound healing, suggesting that cell-matrix adhesion and cell motility are controlled separately, and that phosphorylation of the cytoplasmic domain may be involved in the regulation.
By quantitative proteomic analysis of affinity-purified MLC1 (605908), Lopez-Hernandez et al. (2011) identified HEPACAM as a direct MLC1-binding partner. Immunohistochemistry of human brain tissue showed HEPACAM expression mainly around blood vessels. Double immunostaining with a monoclonal antibody against HEPACAM and a polyclonal antibody against human MLC1 showed that MLC1 and HEPACAM colocalized at astrocytic end-feet in astrocyte-astrocyte junctions. The HEPACAM protein was localized inside axons, in contact regions between myelin and axons, and in cells that surrounded myelin.
Lopez-Hernandez et al. (2011) found no changes in endogenous HEPACAM protein in primary astrocyte culture that had been depleted of MLC1 by RNA interference: HEPACAM was detected in astrocyte-astrocyte processes in MLC1-depleted astrocytes. The studies suggested that HEPACAM subcellular localization is independent of MLC1 expression. Additional in vitro studies showed that both HEPACAM and MLC1 homooligomerize and also heterooligomerize with each other. When coexpressed, both proteins were localized in astrocyte-astrocyte cell junctions. However, MLC1 expressed alone was detected at the plasma membrane, but was not particularly enriched in cell junctions. In contrast, HEPACAM expressed alone was clearly detected in cell junctions. The findings indicated that HEPACAM acts as an escort molecule, necessary to bring MLC1 to cell-cell junctions.
Using various methods, Lanciotti et al. (2012) found that MLC1, TRPV4 (605427), HEPACAM, syntrophin (see 601017), caveolin-1 (CAV1; 601047), Kir4.1 (KCNJ10; 602208), and AQP4 (600308) assembled into an Na,K-ATPase-associated multiprotein complex. In rat and human astrocyte cell lines, this Na,K-ATPase complex mediated swelling-induced cytosolic calcium increase and volume recovery in response to hyposmotic stress. MLC1 associated directly with the Na,K-ATPase beta-1 subunit (ATP1B1; 182330), and plasma membrane expression of MLC1 was required for assembly of the Na,K-ATPase complex. TRPV4 was required for calcium influx, and AQP4 was recruited to the complex following hyposmotic stress.
By immunohistochemical analysis, Sirisi et al. (2014) observed mislocalization of GLIALCAM in Bergmann glia in the cerebellum of a patient with megalencephalic leukoencephalopathy with subcortical cysts-1 (604004) due to mutation in MLC1.
Lanz et al. (2022) demonstrated high-affinity molecular mimicry between the Epstein-Barr virus (EBV) transcription factor EBV nuclear antigen-1 (EBNA1) and the central nervous system protein GlialCAM and provided structural and in vivo functional evidence for its relevance. A crossreactive CSF-derived antibody was initially identified by single-cell sequencing of the paired-chain B cell repertoire of blood and CSF from patients with multiple sclerosis (MS; 126200), followed by protein microarray-based testing of recombinantly expressed CSF-derived antibodies against MS-associated viruses. Sequence analysis, affinity measurements, and the crystal structure of the EBNA1 peptide epitope in complex with the autoreactive antigen-binding fragment (Fab) enabled tracking of the development of the naive EBNA1-restricted antibody to a mature EBNA1-GlialCAM crossreactive antibody. Molecular mimicry was facilitated by phosphorylation of GlialCAM. EBNA1 immunization exacerbated disease in a mouse model of MS, and anti-EBNA1 and anti-GlialCAM antibodies were prevalent in patients with MS.
In 10 patients from 8 families with autosomal recessive megalencephalic leukoencephalopathy with subcortical cysts-2A (MLC2A; 613925), Lopez-Hernandez et al. (2011) identified homozygous or compound heterozygous mutations in the HEPACAM gene (see, e g., 611642.0001-611642.0005). The phenotype was characterized by infantile-onset macrocephaly followed by slowly progressive motor deterioration, with ataxia and spasticity, seizures, and cognitive decline of variable severity. Brain MRI showed typical white matter abnormalities, including cerebral white matter swelling and subcortical cysts, in all stages of the disease. All 16 heterozygous parents were unaffected, but 2 of them had macrocephaly.
In 18 patients from 16 families with autosomal dominant remitting megalencephalic leukoencephalopathy with subcortical cysts-2B with or without impaired intellectual development (MLC2B; 613926), Lopez-Hernandez et al. (2011) identified a heterozygous mutation in the HEPACAM gene (see, e.g., 611642.0006-611642.0008). All the mutations were located in a putative interface of the first immunoglobulin domain. The phenotype was characterized by early-onset macrocephaly associated with cerebral white matter swelling and subcortical cysts. With time, however, the MRI changes improved, and patients had relatively normal motor function, with only some residual hypotonia or clumsiness. About 40% of patients had mental retardation. Eight of 11 parents with a mutant mutated allele had macrocephaly, 1 had transient macrocephaly as a child, and 2 reportedly never had macrocephaly.
In in vitro studies, Lopez-Hernandez et al. (2011) showed that mutant HEPACAM proteins, except S196Y (611642.0001), showed a reduced tendency to homooligomerize compared to wildtype. Mutant HEPACAM proteins showed an altered trafficking, and were located preferentially at the plasma membrane but not in cell junctions, suggesting that homooligomerization is a prerequisite for correct targeting. The recessive pathogenic variants R92Q (611642.0003) and R98C (611642.0005) showed a reduced ability to heterooligomerize with MLC1. In contrast, the recessive mutation S196Y or the dominant mutations R92W (611642.0008) and G89D (611642.0007) retained the capacity to oligomerize with MLC1. Mutant HEPACAM proteins also resulted in mislocalization of MLC1.
Sirisi et al. (2014) found that the zebrafish genome contains 2 GLIALCAM paralogs, glialcama and glialcamb, of which only glialcama exhibited subcellular localization and modulation of the chloride channel Clc2 (CLCN2; 600570) similar to that of mammalian GLIALCAM. Similar to findings in mouse, mlc1 and glialcama colocalized in zebrafish glial cells, especially around brain barriers, radial glia processes and endfeet, and in retinal Muller glia. Mlc1 -/- zebrafish showed minor lesions and megalencephaly in brain, but not myelin vacuolization. However, absence of mlc1 in zebrafish brain, as in mice, led to mislocalization of glialcama. Glialcama mislocalization was not found in cultured Mlc1 -/- mouse astrocytes unless they were exposed to high extracellular potassium, a condition that mimicked neuronal activity.
In 2 sisters with megalencephalic leukoencephalopathy with subcortical cysts-2A (MLC2A; 613925), Lopez-Hernandez et al. (2011) identified compound heterozygosity for 2 mutations in the HEPACAM gene: a 587C-A transversion in exon 3, resulting in a ser196-to-tyr (S196Y) substitution, and a 789G-A transition in exon 4, resulting in a trp263-to-ter (W263X; 611642.0002) substitution. Both mutations occurred in conserved residues in the extracellular domain, and were not found in 400 control chromosomes. Both girls had onset of macrocephaly in the first year of life, followed by neurologic decline in early childhood, manifest as ataxia, spasticity, and cognitive decline. They became wheelchair-bound at ages 7 and 14 years, respectively. Both also developed epilepsy. As adults, they had dysarthria, dysphagia, mental retardation, spasticity, and ataxia. Brain MRI, first performed in adulthood, showed diffuse cerebral white matter swelling, involvement of the posterior limb of the internal capsule, the external capsule, thin corpus callosum, and ventriculomegaly. Both also had subcortical cysts and cerebellar atrophy. Coexpression of wildtype MLC1 and mutant S196Y HEPACAM in rat astrocytes did not show mislocalization of MLC1 or HEPACAM.
For discussion of the 789G-A transition in the HEPACAM gene, resulting in a trp263-to-ter (W263X) substitution, that was identified in compound heterozygous state in 2 sisters with megalencephalic leukoencephalopathy with subcortical cysts-2A (MLC2A; 613925) by Lopez-Hernandez et al. (2011), see 611642.0001.
In a girl with megalencephalic leukoencephalopathy with subcortical cysts-2A (MLC2A; 613925), Lopez-Hernandez et al. (2011) identified compound heterozygosity for 2 mutations in the HEPACAM gene: a 275G-A transition in exon 2, resulting in an arg92-to-gln (R92Q) substitution, and a 631G-A transition in exon 3, resulting in an asp211-to-asn (D211N; 611642.0004) substitution. Both mutations occurred in conserved residues in the extracellular domain and were not found in 400 control chromosomes. The patient had onset of macrocephaly at age 3 months, developed seizures at age 3 years, and ataxia and dysarthria beginning at age 4 years. She became wheelchair-bound at age 7. At age 10, she was mentally retarded with spasticity and ataxia. Brain MRI showed diffuse cerebral white matter swelling and subcortical cysts. Coexpression of wildtype MLC1 (605908) and mutant R92Q HEPACAM in rat astrocytes resulted in diffuse intracellular MLC1 and HEPACAM mislocalization with partial enrichment in cell membranes, but not specifically in cell junctions. Expression of wildtype HEPACAM rescued the defect of the R92Q mutation.
For discussion of the 631G-A transition in the HEPACAM gene, resulting in an asp211-to-asn (D211N) substitution, that was identified in a patient with megalencephalic leukoencephalopathy with subcortical cysts-2A (MLC2A; 613925) by Lopez-Hernandez et al. (2011), see 611642.0003.
In 3 patients, including 2 sibs, with megalencephalic leukoencephalopathy with subcortical cysts-2A (MLC2A; 613925), Lopez-Hernandez et al. (2011) identified a homozygous 292C-T transition in exon 2 of the HEPACAM gene, resulting in an arg98-to-cys (R98C) substitution in a conserved residue in the extracellular domain. The mutation was not found in 400 control chromosomes. Coexpression of wildtype MLC1 (605908) and mutant R98C HEPACAM in rat astrocytes resulted in diffuse intracellular MLC1 and HEPACAM mislocalization with partial enrichment in cell membranes, but not specifically in cell junctions. Expression of wildtype HEPACAM rescued the defect of the R98C mutation.
In 7 patients, including 2 sibs, with remitting megalencephalic leukoencephalopathy with subcortical cysts-2B with or without impaired intellectual development (MLC2B; 613926), Lopez-Hernandez et al. (2011) identified a heterozygous 265G-A transition in exon 2 of the HEPACAM gene, resulting in a gly89-to-ser (G89S) substitution in the putative interface of the first immunoglobulin domain. The mutation occurred de novo in 2 patients, and haplotype analysis excluded a founder effect in the other families with the G89S mutation. The mutation was not found in 400 control chromosomes. All patients developed macrocephaly in the first year of life, and most showed delayed motor development which subsequently resolved. Two patients had mental retardation associated with autism; the remaining 5 patients had normal intelligence. Three of the parents transmitting the mutation had macrocephaly, and 1 had transient macrocephaly as a child.
In a patient with remitting megalencephalic leukoencephalopathy with subcortical cysts-2B with impaired intellectual development (MLC2B; 613926), Lopez-Hernandez et al. (2011) identified a heterozygous 266G-A transition in exon 2 of the HEPACAM gene, resulting in a gly89-to-asp (G89D) substitution in the putative interface of the first immunoglobulin domain. The mutation was not found in 400 control chromosomes. The patient's father, who also carried the mutation, had macrocephaly. Coexpression of wildtype MLC1 (605908) and mutant G89D HEPACAM in rat astrocytes resulted in diffuse intracellular MLC1 and HEPACAM mislocalization with partial enrichment in cell membranes, but not specifically in cell junctions. Expression of wildtype HEPACAM did not rescue the defect of the G89D mutation. The patient developed macrocephaly in the first year of life and showed delayed motor and language development. At age 5.5 years, she was mentally retarded and showed mild hypotonia and clumsiness of the upper limbs. Van der Knaap et al. (2010) reported detailed MRI studies of this patient and noted that she had microcephaly at birth and low birth weight, suggesting preexistent problems. Brain MRI at age 12 months showed diffuse cerebral white matter swelling with involvement of the posterior limb of the internal capsule, the external capsule, and the corpus callosum, as well as temporal cysts. There was much improvement in brain MRI at age 7 years, but she still had mild ventriculomegaly and cysts.
In 6 patients, including 2 sibs, with the remitting type of megalencephalic leukoencephalopathy with subcortical cysts-2B with or without impaired intellectual development (MLC2B; 613926), Lopez-Hernandez et al. (2011) identified a 274C-T transition in exon 2 of the HEPACAM gene, resulting in an arg92-to-trp (R92W) substitution in the putative interface of the first immunoglobulin domain. The mutation was not found in 400 control chromosomes, and haplotype analysis excluded a founder effect. All patients developed macrocephaly in the first year of life, and most showed delayed motor development, which subsequently resolved. The 2 sibs also had impaired intellectual development, and another unrelated patient had impaired intellectual development associated with autism; the remaining 3 patients had normal intelligence. Coexpression of wildtype MLC1 (605908) and mutant R92W HEPACAM in rat astrocytes resulted in diffuse intracellular MLC1 and HEPACAM mislocalization with partial enrichment in cell membranes, but not specifically in cell junctions. Expression of wildtype HEPACAM did not rescue the defect of the R92W mutation.
Favre-Kontula, L., Rolland, A., Bernasconi, L., Karmirantzou, M., Power, C., Antonsson, B., Boschert, U. GlialCAM, an immunoglobulin-like cell adhesion molecule is expressed in glial cells of the central nervous system. Glia 56: 633-645, 2008. [PubMed: 18293412] [Full Text: https://doi.org/10.1002/glia.20640]
Lanciotti, A., Brignone, M. S., Molinari, P., Visentin, S., De Nuccio, C., Macchia, G., Aiello, C., Bertini, E., Aloisi, F., Petrucci, T. C., Ambrosini, E. Megalencephalic leukoencephalopathy with subcortical cysts protein 1 functionally cooperates with the TRPV4 cation channel to activate the response of astrocytes to osmotic stress: dysregulation by pathological mutations. Hum. Molec. Genet. 21: 2166-2180, 2012. [PubMed: 22328087] [Full Text: https://doi.org/10.1093/hmg/dds032]
Lanz, T. V., Brewer, R. C., Ho, P. P., Moon, J.-S., Jude, K. M., Fernandez, D., Fernandes, R. A., Gomez, A. M., Nadj, G.-S., Bartley, C. M., Schubert, R. D., Hawes, I. A., and 18 others. Clonally expanded B cells in multiple sclerosis bind EBV EBNA1 and GlialCAM. Nature 603: 321-327, 2022. [PubMed: 35073561] [Full Text: https://doi.org/10.1038/s41586-022-04432-7]
Lopez-Hernandez, T., Ridder, M. C., Montolio, M., Capdevila-Nortes, X., Polder, E., Sirisi, S., Duarri, A., Schulte, U., Fakler, B., Nunes, V., Scheper, G. C., Martinez, A., Estevez, R., van der Knaap, M. S. Mutant glialCAM causes megalencephalic leukoencephalopathy with subcortical cysts, benign familial macrocephaly, and macrocephaly with retardation and autism. Am. J. Hum. Genet. 88: 422-432, 2011. [PubMed: 21419380] [Full Text: https://doi.org/10.1016/j.ajhg.2011.02.009]
Lopez-Hernandez, T., Sirisi, S., Capdevila-Nortes, X., Montolio, M., Fernandez-Duenas, V., Scheper, G. C., van der Knaap, M. S., Casquero, P., Ciruela, F., Ferrer, I., Nunes, V., Estevez, R. Molecular mechanisms of MLC1 and GLIALCAM mutations in megalencephalic leukoencephalopathy with subcortical cysts. Hum. Molec. Genet. 20: 3266-3277, 2011. [PubMed: 21624973] [Full Text: https://doi.org/10.1093/hmg/ddr238]
Moh, M. C., Lee, L. H., Shen, S. Cloning and characterization of hepaCAM, a novel Ig-like cell adhesion molecule suppressed in human hepatocellular carcinoma. J. Hepatol. 42: 833-841, 2005. [PubMed: 15885354] [Full Text: https://doi.org/10.1016/j.jhep.2005.01.025]
Moh, M. C., Zhang, C., Luo, C., Lee, L. H., Shen, S. Structural and functional analyses of a novel Ig-like cell adhesion molecule, hepaCAM, in the human breast carcinoma MCF7 cells. J. Biol. Chem. 280: 27366-27374, 2005. [PubMed: 15917256] [Full Text: https://doi.org/10.1074/jbc.M500852200]
Sirisi, S., Folgueira, M., Lopez-Hernandez, T., Minieri, L., Perez-Rius, C., Gaitan-Penas, H., Zang, J., Martinez, A., Capdevila-Nortes, X., De La Villa, P., Roy, U., Alia, A., Neuhauss, S., Ferroni, S., Nunes, V., Estevez, R., Barrallo-Gimeno, A. Megalencephalic leukoencephalopathy with subcortical cysts protein 1 regulates glial surface localization of GLIALCAM from fish to humans. Hum. Molec. Genet. 23: 5069-5086, 2014. [PubMed: 24824219] [Full Text: https://doi.org/10.1093/hmg/ddu231]
van der Knaap, M. S., Lai, V., Kohler, W., Salih, M. A., Fonseca, M.-J., Benke, T. A., Wilson, C., Jayakar, P., Aine, M., Dom, L., Lynch, B., Kalmanchey, R., Pietsch, P., Errami, A., Scheper, G. C. Megalencephalic leukoencephalopathy with cysts without MLC1 defect: two phenotypes. Ann. Neurol. 67: 834-837, 2010. [PubMed: 20517947] [Full Text: https://doi.org/10.1002/ana.21980]