Our recent studies have shown that annexin II, expressed on the cell surface of osteoblasts, plays an important role in the adhesion of hematopoietic stem cells (HSCs) to the endosteal niche. NVP-AUY922 arrest-specific 6 (GAS6) receptors AXL, Sky, and Mer, which, in the hematopoietic system, induce dormancy. In addition, GAS6 produced by osteoblasts prevents PCa proliferation and protects PCa from chemotherapy-induced apoptosis. Our results suggest that the activation of GAS6 receptors on PCa in the bone marrow environment may play a critical NVP-AUY922 role as a molecular switch, establishing metastatic tumor cell dormancy. Introduction Nearly 10% of patients whose conditions are diagnosed as PCa initially present with bone metastasis and almost all patients who die of prostate cancers (PCas) have skeletal involvement [1]. Therefore, identifying the mechanisms that control bone metastasis is usually of great consequence to facilitate the design of therapeutics aimed at decreasing metastatic risk and/or their complications. The metastatic process is usually comparable to homing behavior of hematopoietic stem cells (HSCs) to the bone marrow. In marrow, NVP-AUY922 HSCs reside in an area that is usually defined as the stem cell niche. Identification of the HSC niche in marrow has been an active area of investigation. Works in this field have exhibited that several molecules expressed by osteoblasts [2C6] and endothelial cells [7] play critical roles in niche selection. Recently, it was shown that 1) the engraftment of HSCs in lethally irradiated animals during experimental bone marrow transplantation and 2) PCa metastasis to the marrow are dependent on many of the same molecules [8,9]. Several studies have shown that disseminated cells shed from a primary tumor may lay dormant in distant tissues for long periods before they can be activated to form metastases [10C12]. At present, there is usually little information on how dormancy is usually induced or what leads to the activation of the dormant cells. One hypothesis worth considering is usually that molecules that induce HSC dormancy are likely to induce dormancy of metastatic PCa cells. Where adhesion molecules and secreted factors derived from the HSC niche are thought to regulate HSC self-renewal, proliferation, and differentiation [13]. One protein in high large quantity in the marrow is usually annexin II (Anxa2) [14]. Our recent work Rabbit polyclonal to DARPP-32.DARPP-32 a member of the protein phosphatase inhibitor 1 family.A dopamine-and cyclic AMP-regulated neuronal phosphoprotein. has shown that Anxa2 expressed by osteoblasts and endothelial cells plays a critical role in HSC niche selection [15]. More recently, we found that Anxa2 and the Anxa2 receptor (Anxa2r) axis plays a crucial role in establishing bone metastases of PCa [9] by regulating PCa migration, adhesion, and growth in the bone marrow [9]. Blocking Anxa2 or Anxa2r limited short-term and long-term localization of human PCa in murine models, further demonstrating the role of this axis [9]. To further explore the role that Anxa2 plays in the interactions of both PCa and HSCs and the endosteal niche, we added purified Anxa2 protein to PCa cells or uncontrolled) was enhance in PCa after exposure to Anxa2 (unpublished observations). AXL binds to and is usually activated by the growth factor growth arrest-specific 6 (GAS6) NVP-AUY922 [16]. In many systems, including HSCs, GAS6 inhibits cellular proliferation and enhances cell survival [17C22]. Intriguingly, GAS6 expressed by stromal cells slows the cell cycling of HSCs [21]. In the present report, it is usually exhibited that the engagement of Anxa2rs on PCa stimulates the expression of AXL receptors. In contrast with previous reports, we found that GAS6 inhibits PCa proliferation, a situation more closely mimicking that of HSCs. These findings suggest that GAS6 may participate in the induction of tumor cell dormancy so that disseminated cells shed from a primary tumor may lay dormant for prolonged periods in marrow. These observations suggest further parallels between the regulation of HSC function in their endosteal niche and the formation of PCa bone metastases. Materials and Methods Cell Culture PC3 (CRL-1435), DU145 (HTB-81), and LNCaP (CRL-1740) PCa cell lines were obtained from the American Type Culture Collection (Rockville, MD). The metastatic subline LNCaP C4-2B was originally isolated from a lymph node of a patient with disseminated bony and lymph node involvement [23]. SaOS2 (HTB-85) and MG63 (CRL-1427) osteosarcoma cell lines were also obtained from the American Type Culture Collection. PCa cell lines and osteosarcoma cell lines were cultured in RPMI 1640 (Invitrogen, Carlsbad, CA) and Dulbecco’s modified Eagle medium(Invitrogen), respectively. All cultures were supplemented.