SIGLEC12, a human-specific segregating (pseudo)gene, encodes a signaling molecule expressed in prostate carcinomas

Nivedita Mitra, Kalyan Banda, Tasha K. Altheide, Lana Schaffer, Teresa L. Johnson-Pais, Joke Beuten, Robin J. Leach, Takashi Angata, Nissi Varki, Ajit Varki

Research output: Contribution to journalArticlepeer-review

44 Scopus citations


The primate SIGLEC12 gene encodes one of the CD33-related Siglec family of signaling molecules in immune cells. We had previously reported that this gene harbors a human-specific missense mutation of the codon for an Arg residue required for sialic acid recognition. Here we show that this R122C mutation of the Siglec-XII protein is fixed in the human population, i.e. it occurred prior to the origin of modern humans. Additional mutations have since completely inactivated the SIGLEC12 gene in somebut not all humans. The most common inactivating mutation with a global allele frequency of 58% is a single nucleotide frameshift that markedly shortens the open reading frame. Unlike other CD33-related Siglecs that are primarily found on immune cells, we found that Siglec-XII protein is expressed not only on some macrophages but also on various epithelial cell surfaces in humans and chimpanzees. We also found expression on certain human prostate epithelial carcinomas and carcinoma cell lines. This expression correlates with the presence of the nonframeshifted, intact SIGLEC12 allele. Although SIGLEC12 allele status did not predict prostate carcinoma incidence, restoration of expression in a prostate carcinoma cell line homozygous for the frameshift mutation induced altered regulation of several genes associated with carcinoma progression. These stably transfected Siglec-XII-expressing prostate cancer cells also showed enhanced growth in nude mice. Finally, monoclonal antibodies against the protein were internalized by Siglec-XII-expressing prostate carcinoma cells, allowing targeting of a toxin to such cells. Polymorphic expression of Siglec-XII in humans thus has implications for prostate cancer biology and therapeutics.

Original languageEnglish (US)
Pages (from-to)23003-23011
Number of pages9
JournalJournal of Biological Chemistry
Issue number26
StatePublished - Jul 1 2011

ASJC Scopus subject areas

  • Molecular Biology
  • Biochemistry
  • Cell Biology


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