Identification of two subunit A isoforms of the vacuolar H(+)-ATPase in human osteoclastoma.
Subunit A is thought to be the main component of the catalytic site of the vacuolar-type H(+)-ATPase. Screening of a cDNA library made from human osteoclastoma tumor tissue revealed the presence of two isoforms of subunit A. HO68 is a cDNA of 3.1 kilobase pairs, corresponding to a mRNA of approximately 3.4 kilobases in osteoclastoma only, encoding a protein of 615 amino acids with a predicted molecular mass of 68177 Da. A second subtype, VA68, corresponding to a mRNA of approximately 4.8 kilobases was present in all tissues analyzed, and codes for a predicted protein of 617 residues and theoretical molecular mass of 68264 Da. These clones share homology with previously published subunit A sequences, and this, together with the tissue distribution of the mRNA, suggests there are ubiquitous (VA68-type) and tissue-specific (HO68-type) isoforms. HO68 shows the closest sequence homology (95% at the amino acid level) to subunit A of a proton-secreting vacuolar-type H(+)-ATPase located in the apical membrane of midgut goblet cells of tobacco hornworm larva (Manduca sexta). We propose that HO68 could correspond to an isoform of subunit A specific for a vacuolar-type H(+)-ATPase located in the osteoclast plasma membrane.
van Hille
B
B
Research Department, Ciba-Geigy Ltd., Basel, Switzerland.
Richener
H
H
Evans
D B
DB
Green
J R
JR
Bilbe
G
G
D000251:Adenosine Triphosphatases / Q000096:biosynthesis* / Q000378:metabolism; D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D003001:Cloning, Molecular; D004273:DNA, Neoplasm; D005870:Giant Cell Tumors / Q000201:enzymology*; D006801:Humans; D008969:Molecular Sequence Data; D016133:Polymerase Chain Reaction; D017386:Sequence Homology, Amino Acid; D025262:Vacuolar Proton-Translocating ATPases; D014617:Vacuoles / Q000201:enzymology
D004273:DNA, Neoplasm; D000251:Adenosine Triphosphatases; D025262:Vacuolar Proton-Translocating ATPases