HEPARIN HEPARAN SULFATE INTERACTING PROTEIN EXPRESSION AND FUNCTIONS IN HUMAN BREAST-CANCER CELLS AND NORMAL BREAST EPITHELIAL/

Heparin/heparan sulfate interacting protein (HIP) is a recently identi fied protein expressed by many normal epithelia and epithelial cell li nes, In the present study, we examined expression and potential functi ons of this protein in a series of human breast cancer cells and in se ctions of normal and malignant human breast tissue, Four of the five b reast cancer cell lines studied (MCP-7, T-47D, MDA-MB468, and BT-549) expressed HIP protein and mRNA at similar levels. In contrast, MDA-MB- 231 cells failed to display reactivity with HIP-specific probes in any assay, Cell aggregation assays and cell surface antibody binding stud ies demonstrated that HIP was expressed on the cell surface, However, HIP expression did not correlate with the number of cell surface [H-3] heparin (HP) binding sites. The K(Dapp)s for cell surface HP binding s ites were similar in all breast cancer cell lines studied and ranged f rom 112 to 298 nM, In contrast, cell surface HP binding capacity varie d greatly, ranging from 2.3 x 10(5) (MDA-MB-231 and MDA-MB-468) to 99 x 10(5) sites/cell (BT-549), All cell lines tested displayed the abili ty to bind to a heparan sulfate (HS)-binding synthetic peptide moth of HIP in a HP-inhibitable fashion, Binding to this motif was not inhibi ted by other glycosaminoglycans including hyaluronic acid, chondroitin sulfates, or keratan sulfate, Furthermore, cell binding to HIP peptid e was almost completely lost when intact cells were predigested with h eparinases but not chondroitinases. Cell surface HS from breast cancer cells as well as normal human breast epithelia binded to HIP peptide in a HP-inhibitable fashion, demonstrating the ability of these cell s urface components to directly interact, HIP was detected in both norma l breast epithelia and breast tumors in situ. It is suggested that HIP mediates aspects of HS-dependent interactions of both normal and mali gnant breast epithelia with other cells and extracellular matrix compo nents.