Alternative titles; symbols
HGNC Approved Gene Symbol: CAMLG
Cytogenetic location: 5q31.1 Genomic coordinates (GRCh38): 5:134,738,548-134,752,157 (from NCBI)
| Location | Phenotype |
Phenotype MIM number |
Inheritance |
Phenotype mapping key |
|---|---|---|---|---|
| 5q31.1 | ?Congenital disorder of glycosylation, type IIz | 620201 | Autosomal recessive | 3 |
The CAMLG gene encodes a protein that, along with GET1 (602915), forms an ER membrane receptor that enables cytoplasmically facing tail-anchored (TA) proteins to be integrated within the lipid bilayer. The transmembrane domain recognition complex (TRC) is composed of 3 proteins, GET4 (612056), GET5 (UBL4A; 312070), and BAG6 (142590), which target the TA proteins to the membrane. Other proteins involved in this pathway include GET3 (601913), which chaperones proteins to the ER membrane, and STX5 (603189). All are essential for proper functioning of the TRC pathway (summary by Wilson et al., 2022).
Calcium-modulating cyclophilin ligand (CAML) was identified by Bram and Crabtree (1994) in a 2-hybrid screen of a fetal brain cDNA library for signaling molecules that interacted with cyclophilin B (123841). The deduced 296-amino acid protein has a large N-terminal cytoplasmic domain with a central alpha helix and 3 C-terminal transmembrane regions. In vitro translation resulted in a protein with an apparent molecular mass of 33 kD, consistent with its predicted molecular mass. Northern blot analysis detected a 1.35-kb transcript in all tissues examined, with highest expression in testis and brain. Immunolocalization of epitope-tagged CAML in transfected COS cells showed CAML at vesicular-like structures scattered throughout the cytoplasm.
Bram and Crabtree (1994) found that CAML appeared to be involved in regulation of calcium signaling to T lymphocytes and other cells.
Using a yeast 2-hybrid assay, Guo et al. (2005) demonstrated that mouse Caml interacted with Atrap (AGTRAP; 608729). The N-terminal hydrophilic domain of Caml mediated the interaction, and the proteins colocalized in the endoplasmic reticulum (ER). Atrap knockdown increased NFAT (see NFATC2; 600490) activity, and overexpression of Atrap decreased angiotensin II (see 106150)- or Caml-induced NFAT transcriptional activation. Overexpression of the N-terminal ATRAP-interacting domain of Caml increased angiotensin II-induced NFAT promoter activity, whereas overexpression of the C-terminal end of Caml disrupted the effect of angiotensin II on NFAT signaling.
Using yeast 2-hybrid analysis with HIV-1 Vpu protein as bait, followed by coimmunoprecipitation assays and immunofluorescence microscopy, Varthakavi et al. (2008) identified strong interaction with the N terminus of CAML. Expression of human CAML in green monkey cells, in which endogenous Caml has weak binding activity, showed that CAML restricted HIV-1 release. Expression of Vpu or HIV-2 Env overcame CAML-mediated inhibition of viral release. Inhibition of CAML expression with siRNA rescued release of HIV-1 Vpu-negative virus and nonhuman retroviruses. Varthakavi et al. (2008) concluded that CAML is a Vpu-sensitive host restriction factor that inhibits HIV release from human cells.
Using several cell systems, Kuhl et al. (2010) found that tetherin (BST2; 600534), and not CAML, restricted Vpu-mediated retroviral release in HIV-1 nonpermissive cells, in contrast with the findings of Varthakavi et al. (2008). In a retraction, 4 of the authors of Varthakavi et al. (2008) stated that, although they are confident that CAML interacts with HIV-1 Vpu, direct head-to-head comparisons showed that knockdown of tetherin, but not CAML, permitted HIV-1 particle release. They also noted that several other labs were unable to reproduce the restrictive effects of CAML in human cells, and that the report of Kuhl et al. (2010) added to this consensus. Thus, these 4 authors concluded that the report of Varthakavi et al. (2008) should be retracted. However, Varthakavi and 3 other authors of Varthakavi et al. (2008) declined to retract the paper, maintaining that the original observations are correct and reproducible. These 4 authors, in a reply to Kuhl et al. (2010) (Varthakavi et al., 2010), suggested that variation across individual cell clones and other experimental variables may account for the discrepant findings, and they hypothesized that tetherin and CAML inhibit HIV-1 particle release at different steps. Varthakavi et al. (2010) reported that studies using live imaging and electron microscopy supported this hypothesis.
By fluorescence in situ hybridization, Bram et al. (1996) localized the human CAMLG gene to chromosome 5q23, a region known to be syntenic to mouse chromosome 13, which contains Camlg.
Stumpf (2023) mapped the CAMLG gene to chromosome 5q31.1 based on an alignment of the CAMLG sequence (GenBank BC130325) with the genomic sequence (GRCh38).
In a 14-year-old boy, born of consanguineous Turkish parents, with congenital disorder of glycosylation type IIz (CDG2Z; 620201), Wilson et al. (2022) identified a homozygous splice site mutation in the CAMLG gene (601118.0001). The mutation, which was found by trio-based whole-genome analysis, was inherited in an autosomal recessive manner. Analysis of patient fibroblasts showed that the mutation caused skipping of exon 2 and absence of the CAMLG protein. Serum studies identified a combined defect in N- and O-linked glycosylation characterized mostly by undersialylation, indicating late Golgi disruption and suggesting dysfunction of the TRC pathway. Knockdown of the CAMLG gene in HeLa cells led to disorganization of the Golgi. Patient fibroblasts and CAMLG-null HeLa cells showed an increase in STX5 mislocalization to the cytoplasm, again indicating dysfunction of the TRC pathway. Levels of BET1L (615417), another related SNARE protein, were also decreased.
Tran et al. (2003) found that disruption of the Caml gene in mice caused early embryonic lethality. Homozygous mutant blastocysts developed into embryonic stem cells that differentiated into an epithelioid phenotype with retinoic acid. The resulting epithelial cells expressed a functional EGF receptor (EGFR; 131550). However, in the absence of Caml, EGF (131530) stimulation resulted in impaired Egfr recycling and cytoplasmic accumulation of Egfr. Immunoprecipitation analysis indicated a direct interaction between wildtype Caml and Egfr that was dependent on ligand binding. Mutation analysis indicated that Caml bound the kinase domain of Egfr, and the proteins colocalized in the ER.
To avoid embryonic lethality, Tran et al. (2005) generated mice lacking Caml specifically in thymocytes. These mice had reduced numbers of double-positive and single-positive thymocytes, impaired positive selection, enhanced negative selection, and nearly complete loss of peripheral T cells. Caml-deficient thymocytes underwent increased cell death upon T-cell receptor ligation. Caml interacted with Lck (153390) and negatively regulated its activation. Immunoblot analysis and immunofluorescence microscopy demonstrated disrupted localization of Lck in resting and activated Caml-deficient cells. Tran et al. (2005) concluded that CAML is an essential mediator of T-cell survival during thymopoiesis and is important for the regulation of LCK signaling.
In a 14-year-old boy, born of consanguineous Turkish parents, with congenital disorder of glycosylation type IIz (CDG2Z; 620201), Wilson et al. (2022) identified a homozygous A-to-G transition in intron 2 of the CAMLG gene (c.633+4A-G, NM_001745.4), resulting in a splicing defect. The mutation, which was found by trio-based whole-genome analysis, was inherited in an autosomal recessive manner. Analysis of patient fibroblasts showed that the mutation caused the skipping of exon 2, premature termination (Glu58ValfsTer80), and absence of the full-length CAMLG protein. Further studies demonstrated dysfunction of the TRC pathway, resulting in a combined N- and O-glycosylation defect.
Bram, R. J., Crabtree, G. R. Calcium signalling in T cells stimulated by a cyclophilin B-binding protein. Nature 371: 355-358, 1994. [PubMed: 7522304] [Full Text: https://doi.org/10.1038/371355a0]
Bram, R. J., Valentine, V., Shapiro, D. N., Jenkins, N. A., Gilbert, D. J., Copeland, N. G. The gene for calcium-modulating cyclophilin ligand (CAMLG) is located on human chromosome 5q23 and a syntenic region of mouse chromosome 13. Genomics 31: 257-260, 1996. [PubMed: 8824814] [Full Text: https://doi.org/10.1006/geno.1996.0044]
Guo, S., Lopez-Ilasaca, M., Dzau, V. J. Identification of calcium-modulating cyclophilin ligand (CAML) as transducer of angiotensin II-mediated nuclear factor of activated T cells (NFAT) activation. J. Biol. Chem. 280: 12536-12541, 2005. [PubMed: 15668245] [Full Text: https://doi.org/10.1074/jbc.M500296200]
Kuhl, A., Munch, J., Sauter, D., Bertram, S., Glowacka, I., Steffen, I., Sprecht, A., Hofmann, H., Schneider, H., Behrens, G., Pohlmann, S. Calcium-modulating cyclophilin ligand does not restrict retrovirus release. (Letter) Nature Med. 16: 155-157, 2010. [PubMed: 20134461] [Full Text: https://doi.org/10.1038/nm0210-155]
Stumpf, A. M. Personal Communication. Baltimore, Md. 01/19/2023.
Tran, D. D., Edgar, C. E., Heckman, K. L., Sutor, S. L., Huntoon, C. J., van Deursen, J., McKean, D. L., Bram, R. J. CAML is a p56(Lck)-interacting protein that is required for thymocyte development. Immunity 23: 139-152, 2005. [PubMed: 16111633] [Full Text: https://doi.org/10.1016/j.immuni.2005.06.006]
Tran, D. D., Russell, H. R., Sutor, S. L., van Deursen, J., Bram, R. J. CAML is required for efficient EGF receptor recycling. Dev. Cell 5: 245-256, 2003. [PubMed: 12919676] [Full Text: https://doi.org/10.1016/s1534-5807(03)00207-7]
Varthakavi, V., Heimann-Nichols, E., Smith, R. M., Rose, J. Reply to Kuhl et al. (Letter) Nature Med. 16: 157 only, 2010.
Varthakavi, V., Heimann-Nichols, E., Smith, R. M., Sun, Y., Bram, R. J., Ali, S., Rose, J., Ding, L., Spearman, P. Identification of calcium-modulating cyclophilin ligand as a human host restriction to HIV-1 release overcome by Vpu. Nature Med. 14: 641-647, 2008. Note: Retraction: Nature Med. 16: 238 only, 2010. [PubMed: 18500349] [Full Text: https://doi.org/10.1038/nm1778]
Wilson, M. P., Durin, Z., Unal, O., Ng, B. G., Marrecau, T., Keldermans, L., Souche, E., Rymen, D., Gunduz, M., Kose, G., Sturiale, L., Garozzo, D., Freeze, H. H., Jaeken, J., Foulquier, F., Matthijs, G. CAMLG-CDG: a novel congenital disorder of glycosylation linked to defective membrane trafficking. Hum. Molec. Genet. 31: 2571-2581, 2022. [PubMed: 35262690] [Full Text: https://doi.org/10.1093/hmg/ddac055]