Background:
Several years ago, we have identified a number of genes that are differentially regulated in response to androgens and had enriched expression in the prostate, a major target organ for androgens. Two of the genes that we identified in this work are Six TrAnsMembrane Protein of prostate 1 and 2 (STAMP1 and STAMP2) (Korkmaz et al., 2002, 2005; Wellen et al., 2007; Wang et al., 2010; Lindstad et al., 2010(Jin et al., 2015)).
Confocal immunoflourescence microscopy and live cell imaging techniques have shown that STAMPs fused to Green Fluorescent Protein (GFP) are localized in the Golgi/ER and shuttle between these organelles and the plasma membrane. In addition, STAMPs are targeted to the endocytic pathway and may be receptors for a ligand. Furthermore, STAMP1 is highly enriched to prostate for expression and is expressed only in AR positive prostate cancer cell lines whereas STAMP2 is more widely expressed, but its expression is exquisitely androgen regulated. Consistent with a role in cancer development, both STAMP1 and STAMP2 expression is increased in prostate cancer compared with normal prostate. Overexpression of STAMPs in prostate cancer cells increases their proliferation whereas siRNA-mediated knockdown decreases cell growth. Furthermore, both STAMP1 and STAMP2 inhibit apoptosis in prostate cancer cells. Interestingly, STAMP2 knockout mice spontaneously develop all the hallmarks of the metabolic syndrome on a regular diet indicating that it has an important role in regulating metabolism (Wellen et al., 2007; Lindstad et al., 2010). Consistently, STAMP2 also affects metabolic pathways in prostate cancer cells. Futhermore, STAMP2 is involved in regulating macrophage inflammatory responses and atherosclerosis in mouse models (ten Freyhaus et al., 2012). Interestingly, nanoliposomal STAMP2 specific siRNA delivery in mice results in dramatic tumor regression in two independent models of prostate cancer (Figure 1). These findings warrant more detailed analysis of STAMP function in normal cells, as well as under pathological conditions.
In parallel to functional characterization of STAMPs, we have discovered that androgen signaling significantly regulates the endoplasmic reticulum (ER) stress pathways and the response to it, the unfolded protein response (UPR) ((Sheng et al., 2015)). We found that androgen receptor (AR) directly activated one of the canonical arms of the UPR, inositol-requiring enzyme 1 (IRE1) pathway (Figure 2). Consistent with the importance of IRE1 signaling in prostate cancer, its genetic or pharmacological inhibition dramatically inhibited prostate cancer growth in vitro and in vivo (Sheng et al., 2015).In keeping with these observations IRE1 expression, and its gene signature, are deregulated in human prostate cancer specimens. Further characterization of IRE1 in prostate cancer progression is in progress.
Projects:
Various lines of investigation are under way regarding the STAMPs and stress signaling using similar approaches. For each project, the incoming MSc student will work with a postdoctoral fellow and/or a Ph.D. candidate. The two different areas are summarized below:
Project 1. Characterization of the interacting partners of STAMPs and the respective signaling pathways. The knowledge of the interacting partners of any protein is important to delineate their function in the cell. We have thus used the yeast two-hybrid assay and identified several potential STAMP interactors. The validation of the interactors for STAMPs and their functional consequence(s), if any, is in progress, and has already been established for some of the interactors. The different lines of investigation in this project is to carry these forward, validate them in prostate cancer cells, and determine if they have functional consequences in vivo. To that end, several approaches are being used. First, coimmunoprecipitation assays are utilized to study the interactions in vivo. Second, GST-pulldown assays are used to complement the coimmunoprecipitations and study interactions in more detail. Third, possible colocalization in cells is determined by immunoflourescence microscopy. Foruth, functional interactions are assessed based by using a variety of assays based on the interacting protein involved.
Project 2. Functional analysis of ER stress pathways in prostate cancer cells. As noted above, we have strong evidence for the involvement of ER stress and IRE1 signaling on prostate cancer cell biology. Building on our current findings, we are investigating the possible mechanisms through which AR-IRE1 signaling axis increases proliferation and inhibits apoptosis. The goal of the studies in this project is to use both cell lines in vitro, as well as xenografts in vivo, to determine the exact molecular mechanisms that are involved. We have established both genetic manipulation as well as pharmacological targeting of this pathway to evaluate its potential as a therapeutic target in prostate cancer.
For questions and more information, please contact Fahri Saatcioglu at 22854569, fahris@ibv.uio.no, Rm. 3611. We are especially interested in those students who are already considering a career in science and would like to work in an internationally competitive laboratory. For more detailed information on the projects and the lab, please see our website
References:
Jin, Y., Qu, S., Wang, L., Kristian, A., Maelandsmo, G.M., Jeronimo, C., Teixeira, M.R., Tekedereli, I., Sood, A., Lopez-Berestein, G., Ozpolat, B., Danielsen, H., and Saatcioglu, F. (2013). Kallikrein 4 integrates androgen and mTOR signalling in prostate cancer. Proc. Nat. Acad. Sci. USA 110(28):E2572-81.
Jin, Y., Wang, L., Qu, S., Kristian, A., Mælandsmo, G.M., Yuca, E., Tekedereli, I., Gorgulu, K., Alpay, N., Sood, A., Lopez-Berestein, G., Fazli, L., Rennie, P., Risberg, B., Wæhre, H., Danielsen, H.D., Ozpolat, B.,and Fahri Saatcioglu (2015). STAMP2 increases oxidative stress and is critical for prostate cancer. EMBO Mol Med, 7(3):315-31
Klokk, T.I., Kilander, A., Xi, Z., Wæhre, H., Risberg, B., Danielsen, H.E., and Saatcioglu, F. (2007). Kallikrein 4 is a proliferative factor that is overexpressed in prostate cancer. Cancer Res. 67, 5221-5230.
Korkmaz, K., Elbi, C., Korkmaz, C., Kurys, P., Hager, G., Loda, M., and Saatcioglu, F. (2002). Cloning and characterization of STAMP1--A highly prostate restricted six transmembrane protein overexpressed in prostate cancer. J. Biol. Chem. 277, 36689-96696.
Korkmaz, C., Korkmaz, K., Kurys, P., Elbi, C., Klokk, T.I., Hammarstrom, C. Svindland, A., Hager, G., and Saatcioglu, F. (2005). Molecular cloning and characterization of STAMP2, an androgen regulated six-trans-membrane protein that is overexpressed in a subset of prostate cancers. Oncogene 24, 4934-4945.
Lindstad, T., Jin, Y., Wang, L., Qu, S., Saatcioglu, F. (2010). STAMPs at the crossroads of cancer and nutrition. Nutr Cancer 62:891-895.
Sikkeland, J., and Saatcioglu, F. (2013). Differential regulation and function of STAMP family proteins during adipogenesis. PloS One 8(7):e68249.
Sheng, X., Arnoldussen, Y.W., Storm, M., Tesikova, M., Jin, Y., Nenseth, H.Z., Sen Zhao, S., Mills, I.G., Fazli, L., Rennie, P., Risberg, B., Wæhre, H., Danielsen, H.E. Hotamisligil, G.S., and Saatcioglu, F. (2015). Divergent androgen regulation of unfolded protein response pathways drives prostate cancer. EMBO Mol Med, e201404509.
Wellen, K.E., Fucho, R., Gregor, M.F., Furuhashi, M., Morgan, C., Lindstad, T., Gorgun, C., Vaillencourt, C., Saatcioglu, F., and Hotamisligil, G.S. (2007). Coordinated regulation of nutrient and inflammatory responses by STAMP2 is essential for metabolic homeostasis. Cell 129, 537-548.