Heparin/heparan sulfate interacting protein expression and functions in human breast cancer cells and normal breast epithelia.
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Heparin/heparan sulfate interacting protein (HIP) is a recently identified protein expressed by many normal epithelia and epithelial cell lines. In the present study, we examined expression and potential functions of this protein in a series of human breast cancer cells and in sections of normal and malignant human breast tissue. Four of the five breast cancer cell lines studied (MCF-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 studies demonstrated that HIP was expressed on the cell surface. However, HIP expression did not correlate with the number of cell surface [3H]heparin (HP) binding sites. The K(Dapp)s for cell surface HP binding sites were similar in all breast cancer cell lines studied and ranged from 112 to 298 nM. In contrast, cell surface HP binding capacity varied 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 ability to bind to a heparan sulfate (HS)-binding synthetic peptide motif of HIP in a HP-inhibitable fashion. Binding to this motif was not inhibited by other glycosaminoglycans including hyaluronic acid, chondroitin sulfates, or keratan sulfate. Furthermore, cell binding to HIP peptide was almost completely lost when intact cells were predigested with heparinases 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 surface components to directly interact. HIP was detected in both normal breast epithelia and breast tumors in situ. It is suggested that HIP mediates aspects of HS-dependent interactions of both normal and malignant breast epithelia with other cells and extracellular matrix components.
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