Cloning and characterization of MN, a human tumor-associated protein with a domain homologous to carbonic anhydrase and a putative helix-loop-helix DNA binding segment

Oncogene. 1994 Oct;9(10):2877-88.


MN is a transmembrane glycoprotein that has been detected in HeLa cells and in some human carcinomas. The expression of MN protein in HeLa cells is regulated by cell density. In HeLa x fibroblast cell hybrids its expression correlates with tumorigenicity. Using a specific monoclonal antibody we have identified a cDNA clone coding for MN. Analysis of the deduced amino acid sequence revealed strong structural homology between the central region of the MN protein and carbonic anhydrases (CA). MN sequence retains the conserved zinc-binding site as well as the enzyme's active center. In accord with these findings, MN protein from HeLa cells was found to bind zinc and to have carbonic anhydrase activity. The N-terminal region of MN shares some similarity with DNA binding proteins of the helix-loop-helix (HLH) family, and the protein was found to have affinity for DNA by DNA-cellulose chromatography. The region between the CA-like domain and the putative HLH domain is rich in imperfect repeats of serine, proline, glycine and acidic residues with few hydrophobic amino acids, resembling thus an activation region of transcription factors. The fact that MN protein is detectable in several types of human carcinomas, but not in corresponding non-cancerous tissues, suggests its possible role in neoplasia. In addition, the analysis of biological consequences of MN expression of NIH3T3 cells provides the evidence in favour of MN protein involvement in control of cell proliferation and transformation.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • 3T3 Cells
  • Amino Acid Sequence
  • Animals
  • Antigens, Neoplasm*
  • Base Sequence
  • Carbonic Anhydrase IX
  • Carbonic Anhydrases / chemistry*
  • Cloning, Molecular
  • DNA, Neoplasm
  • DNA-Binding Proteins / chemistry
  • DNA-Binding Proteins / genetics*
  • Glycosylation
  • HeLa Cells
  • Helix-Loop-Helix Motifs*
  • Humans
  • Mice
  • Molecular Sequence Data
  • Neoplasm Proteins / chemistry
  • Neoplasm Proteins / genetics*
  • Protein Biosynthesis
  • RNA, Messenger / genetics
  • Sequence Homology, Amino Acid
  • Zinc / metabolism


  • Antigens, Neoplasm
  • DNA, Neoplasm
  • DNA-Binding Proteins
  • Neoplasm Proteins
  • RNA, Messenger
  • CA9 protein, human
  • Carbonic Anhydrase IX
  • Carbonic Anhydrases
  • Zinc

Associated data

  • GENBANK/X66839