ALCAM gene is 210,200 bp long and resides on the positive strand on DNA. The gene has a total of 16 exons.

ALCAM gene codes for 9 transcripts, 4 of them are protein coding (4701, 4189, 2496, 1818 bp) and 5 of them are non-protein coding transcripts (2845, 1770, 1242, 783, 564 bp).

No reported pseudogenes for ALCAM.

ALCAM is a glycoprotein of the immunoglobulin superfamily and has an estimated molecular weight of 100-105 kDa.

ALCAM is expressed in almost every tissue. Higher expression is observed in parathyroid gland. Tissues with medium ALCAM expression are cerebral cortex, cerebellum, thyroid gland, tonsil, nasopharynx, bronchus, lung, liver, gallbladder, pancreas, salivary gland, stomach, urinary bladder, kidney, epididymis, prostate, seminal vesicle, breast, cervix, uterine, endometrium and fallopian tube. Tissues with low expression are hippocampus, caudate, adrenal gland, appendix, lymph node, oral mucosa, rectum, duodenum, small intestine, colon, ovary, placenta, soft tissue and skin. Spleen, bone marrow, heart muscle, smooth muscle, skeletal muscle, esophagus, testis, vagina and adipose tissue have no ALCAM expression (The Human Protein Atlas, http://www.proteinatlas.org/).

ALCAM protein is localized to the cell membrane (Bowen et al., 1995).

ALCAM is a type-I transmembrane protein, which belongs to the immunoglobulin superfamily (Bowen et al., 1995). It constitutes 5 immunoglobulin-like domains and a short COOH-terminal cytoplasmic tail (Weidle et al., 2010). ALCAM was first shown as a ligand of CD6 on activated leukocytes (Whitney et al., 1995). Then, it was found on hematopoietic stem cells and myeloid progenitors (Swart, 2002). ALCAM-CD6 interaction mediates T-cell activation or proliferation. In addition, ALCAM-ALCAM homophilic interaction contributes to cellular changes, such as angiogenesis, immune response and cell migration during the neuronal development (van Kempen et al., 2001). The expression of ALCAM was found during organ development in the central and peripheral nervous system, sensory organs, hematopoiesis, endothelial and epithelial lineage (Swart, 2002). Furthermore, a short ALCAM transcript leads to a soluble isoform of ALCAM (sALCAM). This isoform has only one immunoglobulin-like domain (D1), which is important for ligand binding (Ikeda and Quertermous, 2004). The roles of sALCAM were considered to block hemophilic binding of ALCAM and endogenous ALCAM function (Swart, 2002). Moreover, sALCAM was also shown to inhibit tumor progression in melanoma cells (van Kilsdonk et al., 2008).

There are only a few reported mutations in ALCAM. One of the known cases is the deletion of ALCAM at 3q13.1 in a keratocystic odontogenic tumor. This mutation is thought to contribute to a matrix metalloproteinase-mediated proteolytic cascade, leading to tumor growth (Heikinheimo et al., 2007). In addition, it was reported that deletion of ALCAM might be related to craniofacial abnormalities (Simovich et al., 2008).

ALCAM promoter contains several cis-acting elements including RELA (p65 NF-kB) binding motif. This motif has several CpG residues and it is highly methylated in breast cancer cells, resulting with loss of ALCAM expression (King et al., 2010). Hypermethylation of ALCAM promoter was also observed in preeclampsia placentas (Yeung et al., 2016).