User:Curtwarren

Perlecan and Reactive Stroma
A great conundrum dominates prostate cancer research: why do prostate cancer cells home to bone? Greater than 90% of prostate cancer metastases go to the bone marrow. This rapidly-turned-over tissue can change in response to prostate cancer invasion – the cells that are affected by this are termed “reactive stroma” (Edlund et al., 2004). Similarly, prostate cancer cells undergo certain changes, such as epithelial-to-mesenchymal transition, that correspond with progression, which itself corresponds with metastasis to bone (Hugo et al., 2007). One of the gene products upregulated during prostate cancer adaptation to survival in bone marrow is the heparan sulfate proteoglycan, perlecan (Savoré et al., 2005). Expression of perlecan is crucial to the tumorigenicity of bone-adapted prostate cancer cells (Savoré et al., 2005) and is the highest of all proteoglycans in the bone marrow microenvironment (Schofield et al., 1999). Something in the bone marrow microenvironment makes it ultimately favorable for the growth of osteoblastic prostate cancer cells; I will test the hypothesis that the presence of perlecan in the stroma contributes to this permissiveness.

Bone Metastasis of prostate cancer
The bone marrow microenvironment ultimately favors the growth of prostate cancer cells. This microenvironment facilitates transdifferentiation of prostate cancer cells including osteomimicry/EMT and neuroendocrine differentiation (NED) (Xu et al., 2006) – Figure 1. This phenomenon is in part a result of changes in the reactive bone marrow stromal cells upon cancer cell colonization of the stroma. Bone marrow or prostate stromal cells with direct interactions with cancer cells are classified as reactive stromal cells. Reactive stromal cells undergo a number of changes in gene expression (figure 1 – adapted from (Josson et al.). This bi-directional interaction between cancer cells and stromal cells certainly plays a key role in both priming the metastatic site (the bone) and the cancer cells for survival in distant sites in the bone.  Transdifferentiation of prostate cancer cells most often leads to what are referred to as “osteoblastic” lesions in the bone marrow (Koutsilieris et al., 1987) – these tumors create a signaling cascade that causes bone to form in a disorganized, unstable matrix of “woven” bone (Aoki et al., 1987).  This leads to increased incidence of fractures and bone pain, decreasing the quality of life for patients.  In addition to decreased quality of life, bone metastases are essentially untreatable – discovering a means for inhibiting the metastasis of prostate cancer to bone, or killing cells once they have colonized the bone, is the ultimate translational goal of prostate cancer research. This study will primarily focus on the response of the human bone marrow stromal cell lines, HS-5 and HS-27a to the presence of prostate cancer cells and to treatment with growth factors and cytokines which are important to prostate cancer progression and prevalent in the bone marrow microenvironment. These cell lines are accepted as the “gold standard” for representation of the in vivo population of bone marrow stromal cells (Torok-Storb et al., 1999). HS-5 is thought to represent the “secretory” population of stromal cells, releasing high levels of cytokines and growth factors, whereas HS-27a represents the “structural” population of stromal cells, supporting the characteristic “cobblestone” morphology of hematopoietic progenitor cells in co-culture (Torok-Storb et al., 1999). These cell lines express perlecan endogenously and have been used to model reactive stroma in culture (O'Connor et al., 2007). Perlecan and prostate cancer. During tumor growth, after the tumor has broken through the basement membrane of the prostate duct, reactive stromal cells in the prostate increase their expression of the heparan-sulfate proteoglycan, perlecan (figure 2). The role of perlecan in reactive stroma is unclear. In normal stroma and basement membrane the function of the intact core protein and N-and C-terminal heparan sulfate chains are many; individual fragments of perlecan can have separate functions upon degradation of the intact molecule (Bix et al., 2004). Heparan sulfate-mediated binding of growth factors in the extracellular matrix is crucial for delivery of various growth factors to their cellular receptors (Jiang and Couchman, 2003). For example, regulation of Sonic Hedgehog signaling by the heparan sulfate chains of perlecan are crucial to prostate cancer cell growth in vitro (Datta et al., 2006). Regardless of the reason for stromal cell activation of perlecan expression in reaction to tumorigenesis, at some point during tumor progression, perlecan expression becomes crucial to further growth of cancer cells. Knockdown of perlecan expression by ribozymes in C4-2B cells decreases tumor growth in mouse xenograft models and decreases the response to heparin-binding growth factors in vitro (Savoré et al., 2005). It is possible that the increase in TGF-β signaling in reactive stroma which leads to SMAD3-driven FGF-2 signaling (Yang et al., 2008) is what leads to upregulation of perlecan in reactive stroma. This signaling also may be part of the pathway pre-conditioning prostate cancer cells to metastasize to the bone marrow, an environment rich in both perlecan and TGF-β. Evidence strongly suggests that perlecan expression by both prostate cancer cells and stromal cells is part of the metastatic cascade leading to bone lesions in prostate cancer.