Interaction of uteroglobin with lipocalin-1 receptor suppresses cancer cell motility and invasion.

Cellular migration and invasion are critical for important biological processes including cancer metastasis. We previously reported that uteroglobin (UG), a multifunctional secreted protein, binds to several cell types inhibiting migration and invasion [G.C. Kundu, A.K. Z. Zhang Mandal, G. Mantile-Selvaggi, A.B. Mukherjee (1998) Uteroglobin (UG) suppresses extracellular matrix invasion by normal and cancer cells that express the high affinity UG-binding proteins. J Biol Chem. 273: 22819-22824]. More recently, we reported that HTB-81 adenocarcinoma cells, which do not bind UG, are refractory to UG-mediated inhibition of migration and invasion [Z. Zhang, G.C. Kundu, D. Panda, A.K. Mandal et al. (1999) Loss of transformed phenotype in cancer cells by overexpression of the uteroglobin gene. Proc Natl Acad Sci U S A. 96, 3963-3968]. Since UG shares several biological properties with lipocalin-1 that mediates some of its biological effects via its receptor (Lip-1R), we sought to determine whether UG might interact with Lip-1R and inhibit migration and invasion of HTB-81 cells. To address this question, we first transfected COS-1 cells, which do not bind UG, with a Lip-1R-cDNA construct and performed binding assays using 125I-human UG (hUG). The results show that hUG binds Lip-1R on these cells with high specificity. Further, transfection of HTB-81 cells with the same construct yielded 125I-hUG binding with high affinity (Kd=18 nM) and specificity. The hUG-Lip-1R interaction was further confirmed by transfecting HTB-81, HTB-30 and HTB-174 cells, which are refractory to UG-binding, with a green fluorescent protein (GFP)-Lip-1R-cDNA construct and testing for Lip-1R-hUG colocalization by fluorescence microscopy. Finally, we demonstrate that Lip-1R-hUG interaction on Lip-1R transfected HTB-81 cells renders them fully responsive to hUG-mediated inhibition of migration and invasion. Taken together, these results suggest that Lip-1R is at least one of the UG-binding proteins through which UG exerts anti-motility and anti-invasive effects.