CDNA CLONING AND EXPRESSION OF HIP, A NOVEL CELL-SURFACE HEPARAN SULFATE HEPARIN-BINDING PROTEIN OF HUMAN UTERINE EPITHELIAL-CELLS AND CELL-LINES/

Heparan sulfate proteoglycans and their corresponding binding sites ha ve been suggested to play an important role during the initial attachm ent of murine blastocysts to uterine epithelium and human trophoblasti c cell lines to uterine epithelial cell lines. Previous studies on RL9 5 cells, a human uterine epithelial cell line, had characterized a sin gle class of cell surface heparin/heparan sulfate (HP/HS)-binding site s. Three major HP/HS-binding peptide fragments were isolated from cell surfaces by tryptic digestion, and partial amino-terminal amino acid sequence for each peptide fragment was obtained (Raboudi, N., Julian, J., Rohde, L. H., and Carson, D. D. (1992) J. Biol. Chem. 267, 11930-1 1939). In the current study, using approaches of reverse transcription -polymerase chain reaction and cDNA library screening, we have cloned and expressed a novel, cell surface HP/HS-binding protein, named HP/HS interacting protein (HIP), from RL95 cells. The full-length cDNA of H IP encodes a protein of 159 amino acids with a calculated molecular ma ss of 17,754 Da and pI of 11.75. Transfection of HIP full-length cDNA into NIH 3T3 cells demonstrated cell surface expression and a size sim ilar to that of HIP expressed by human cells. Predicted amino acid seq uence indicates that HIP lacks a membrane spanning region and has no c onsensus sites for glycosylation. Northern blot analysis detected a si ngle transcript of 1.3 kilobases in both total RNA and poly(A(+)) RNA. Examination of human cell lines and normal tissues using both Norther n blot and Western blot analyses revealed that HIP is expressed at dif ferent levels in a variety of human cell lines and normal tissues but absent in some cell lines and some cell types of normal tissues examin ed. HIP has relatively high homology (similar to 80% both at the level s of nucleotide and protein sequence) to a rodent ribosomal protein L2 9. Thus, members of the L29 family may be displayed on cell surfaces w here they may participate in HP/HS binding events.