Testisin, a new human serine proteinase expressed by premeiotic testiculargerm cells and lost in testicular germ cell tumors

We have cloned and characterized a cDNA encoding a new human serine protein ase, testisin, that is abundantly expressed only in the testis and is lost in testicular tumors. The testisin cDNA was identified by homology cloning using degenerate primers directed at conserved sequence moths within the ca talytic regions of serine proteinases, It is 1073 nucleotides long, includi ng 942 nucleotides of open reading frame and a 113-nucleotide 3' untranslat ed sequence. Northern and dot blot analyses of RNA from a range of normal h uman tissues revealed a 1.4-kb mRNA species that was present only in testis , which was not detected in eight of eight testicular tumors. Testisin cDNA is predicted to encode a protein of 314 amino acids, which consists of a 1 9-amino acid (aa) signal peptide, a 22-aa proregion, and a 273-aa catalytic domain, including a unique 17-aa COOH-terminal hydrophobic extension that is predicted to function as a membrane anchor. The deduced amino acid seque nce of testisin shows 44% identity to prostasin and contains features that are typical of serine proteinases with trypsin-like substrate specificity, Antipeptide antibodies directed against the testisin polypeptide detected a n immunoreactive testisin protein of M-r 35,000-39,000 in cell lysates from COS-7 cells that were transiently transfected with testisin cDNA, Immunost aining of normal testicular tissue showed that testisin was expressed in th e cytoplasm and on the plasma membrane of premeiotic germ cells. No stainin g was detected in eight of eight germ cell-derived testicular tumors. In ad dition, the testisin gene was localized by fluorescence irt situ hybridizat ion to the short arm of human chromosome! 16 (16p13.3), a region that has b een associated with allellic imbalance and loss of heterozygosity in sporad ic testicular tumors. These findings demonstrate a new cell surface serine proteinase, loss of which may have a direct or indirect role in the progres sion of testicular tumors of germ cell origin.