Abstract P5-07-08: Identification and characterization of a new TIMP-1 binding protein
Authors: Moreira José M , Høeberg Mikkel , Ulrik Lademann Ulrik , Viuff Birgitte , Jensen Lena V , Stenvang Jan , Nygård Sune B , Ørum-Madsen Maj S , Vistesen Mette V , Fuglsang Anja T , Liu Siqi , Brünner Nils 
Published: May 2015

Abstract
Tissue inhibitor of metalloproteinases 1 (Timp-1), is one of the four known endogenous inhibitors of matrix metalloproteinases (MMPs); in recent years, Timp-1 has become increasingly recognized as a multifunctional protein that, independently of its MMP inhibitory activity, is able to regulate core cellular processes such as cell proliferation and apoptosis. Consistent with this pro-survival function, Timp-1 expression was shown to be able to protect cancer cells from epirubicin or paclitaxel-mediated cytotoxicity. Consistent with this effect, clinical studies have shown high Timp-1 tumor levels to be predictive of resistance to adjuvant anthracycline-based chemotherapy in metastatic breast cancer patients. In spite of abundant evidence directly involving Timp-1 in regulation of cell growth and apoptosis, the downstream mechanisms of Timp-1–mediated cell signaling underlying these effects, and its biological consequences, have remained unclear. In order to address this issue, we aimed to identify cellular binding partners for Timp-1, which may be able to induce signaling. Therefore, we performed yeast two hybrid screening using a mammary gland cDNA library. We report here the identification of a novel Timp-1 interactor, CD74. CD74, also known as MHC class II invariant chain (li), was mainly thought to function as an MCH class II chaperone promoting the exit of MHC class II molecules from the endoplasmic reticulum (ER). However, a fraction of cellular CD74 has been found to traffic to the plasma membrane where it functions as an accessory-signaling molecule, being quickly recycled back into the endosomal pathway.
The interaction between TIMP-1 and CD74 was confirmed by co-immunoprecipitation studies in the triple negative breast cancer cell line MDA-MB-231, and we showed that CD74 is necessary for Timp-1 cellular internalization and Timp-1-mediated activation of Akt signaling. To determine the applicability of our findings to a broader context, we analyzed a breast cancer patient cohort for expression of CD74, CD63 and Timp-1 by immunohistochemistry (IHC) and in situ hybridization (ISH). We found that cancer cells which were negative for TIMP-1 mRNA but positive for Timp-1 protein, indicating an active transport of Timp-1 into the cells. These results raise the possibility that CD74 may be a useful target for effecting Timp-1 mediated chemoresistance.
Citation Format: José M Moreira, Mikkel Høeberg, Ulrik Ulrik Lademann, Birgitte Viuff, Lena V Jensen, Jan Stenvang, Sune B Nygård, Maj S Ørum-Madsen, Mette V Vistesen, Anja T Fuglsang, Siqi Liu, Nils Brünner. Identification and characterization of a new TIMP-1 binding protein [abstract]. In: Proceedings of the Thirty-Seventh Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2014 Dec 9-13; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2015;75(9 Suppl):Abstract nr P5-07-08.