KAI1

CD82
Kangai (chinese for anticancer) 1
Leukocyte surface antigen R2 (SAR2), R2 leukocyte antigen
Suppressor of tumorigenicity 6 (ST6)

Gene: maps to 11p11.2 (Dong J.T. et al., 1995). About 80 kb of DNA was identified as the KAI1 gene, which contains 8 kb of 5'-region, 10 exons, 9 introns, and 8 kb of DNA following exon 10. The coding region starts in exon 3 and ends in exon 10. The size of intron 1 is 29 kb, which almost equals the sizes of all other introns combined. A CpG island is present in the 5'-promoter region and extends to exon 1 and intron 1. The promoter region has no TATA or CCAAT box but has many putative binding motifs for various transcription factors, including nine Sp1 sites and five AP2 sites. These results suggest a diverse regulatory mechanism for the expression of the KAI1 gene in human tissues. The transcription initiation site of the KAI1 gene is located 181 bp upstream of the first nucleotide of the translation initiation codon. Comparisons of gene structures between KAI1 and seven other members of the transmembrane 4 superfamily revealed that the splicing sites relative to the different structural domains of the predicted proteins are well conserved, suggesting that these genes are evolutionarily related and that they arose through gene duplication and divergent evolution (Dong J.T. et al., 1997).
mRNA: size: ~2.0 kb.
Protein: a tetraspanin containing 267 amino acids, with 4 hydrophobic and presumably transmembrane domains and 1 large extracellular hydrophilic domain with 3 potential N-glycosylation sites. Tetraspanins are proteins from the transmembrane 4 superfamily (TM4SF); they form membrane complexes with integrin receptors and are implicated in integrin-mediated cell migration. KAI1 is evolutionarily conserved, is expressed in many human tissues, and encodes a member of a structurally distinct family of leukocyte surface glycoproteins. Decreased expression of this gene may be involved in the malignant progression of prostate and other cancers.

Cell lines:

Tumors:
- Quantitative RT-PCR analysis was performed to evaluate the expression of KAI1 in 109 breast tumors. 65 tumors were KAI1/CD82 negative. The disease-free survival rate of patients with KAI1/CD82-negative tumors appeared significantly lower than that of patients with KAI1/CD82-positive tumors (Huang C.I. et al., 1998).

Dong J.T. et al. (1995) KAI1, a metastasis suppressor gene for prostate cancer on human chromosome 11p11.2. Science 268, 884-886.
Dong J.T. et al. (1997) Genomic organization of the human KAI1 metastasis-suppressor gene. Genomics 41, 25-32.
Huang C.I. et al. (1998) Correlation of reduction in MRP-1/CD9 and KAI1/CD82 expression with recurrences in breast cancer patients. Am. J. Pathol. 153, 973-983.