• Identifying the key players in osteopontin/alpha(v)beta(3)-mediated migration and invasion of metastatic prostate cancer cells

      Desai, Bhavik; Chellaiah, Meenakshi A. (2008)
      Advanced stages of prostatic carcinoma have a high incidence of metastases to the bones. Our research examines the mechanisms that can facilitate local invasion of prostate cancer (PC) cells inside the extracellular matrix (ECM) of bone. PC3 is a stable cancer cell line derived from bony metastasis of prostate cancer. Osteopontin (OPN), which is an autocrine motility factor secreted by both osteoclasts and osteoblasts, is an important component of the ECM in bone. PC3 cells degrade ECM by secretion of matrix metalloproteinases (MMP-s), primarily through secretion of active MMP-9. Experimental approaches that employed both an over expression and knockdown of endogenous OPN in PC3 cells demonstrated that OPN regulates migration of PC3 cells by increasing active MMP-9 secretion. OPN-mediated upregulation of MMP-9 expression and secretion occurs in response to activation of the hyaluronan receptor CD44. Bisphosphonate-mediated inhibition of Rho kinase, which is an upstream activator of CD44, attenuated the stimulatory effects of OPN on both migration and secretion of MMP-9. In addition to a standard form, multiple CD44 isoforms exist in several cell systems. We have identified CD44 isoforms, which exist in PC3 cells. At the cellular level, migration is a consequence of increased MMP activity in conjunction with changes in the actin cytoskeleton. PC3 cells exhibited punctate evaginations (similar to invadopodia), enriched in actin, which could degrade the underlying gelatin matrix. MMP-9 activity was essential for the invasiveness of invadopodia, but had no role in their formation. The WAVE protein family member WASP was observed to have a role in actin polymerization in PC3 cells. Active MMP-9 was demonstrated to be associated with WASP, thereby pointing out to a mechanistic possibility of WASP's association to MMP-9, with or without an intervening adaptor protein. OPN increased the incidence of invadopodia formation as well as WASP co-localization with invadopodia. The contiguous activation from OPN, CD44, and MMP-9 to WASP and dynamic actin changes provides deeper insight into OPN-mediated PC3 cell invasion and paves the way for therapeutically targeting this pathway in future.
    • The Role of Semaphorin 4D (Sema4D) in Bone Metastasis

      Buhamrah, Asma; Basile, John R. (2014)
      The Role of Semaphorin 4D (Sema4D) in Bone Metastasis Background: Bone metastasis is a catastrophic endpoint of many neoplastic diseases, but especially for patients with advanced breast cancer. Despite the continuous advances in pharmacological and cancer research, bone loss and subsequent bone complications are seen in 70% of females diagnosed with breast cancer. Semaphorin 4D (Sema4D), a protein originally described to regulate the immune response, is now known to have a novel role in bone regulation. Sema4D is also found to be highly expressed by many tumor cells including those of breast cancer. In this study we focus on the role of Sema4D produced by tumor cells on their ability to metastasize to bone. Materials and methods: The osteoblast cell line MC3T3 was treated under different osteogenic conditions to examine the effects of Sema4D on bone differentiation in vitro. We also used tumor cells with silenced Sema4D to investigate the effects of tumor-derived Sema4D on their ability to metastasize to bone in vivo. Results: Sema4D produced by the breast cancer cell line MDA-231 inhibited bone matrix formation and mineralization in vitro. In vivo, however, MDA-231 tend to spread to bone only when Sema4D was highly expressed by these cells and not when it was silenced. Conclusion: Over-expression of Sema4D by breast cancer cells inhibits bone formation in vitro and tends to increase the ability of these cells to metastasize to bone in vivo and establish osteolytic lesions characterized by this tumor type. Our findings may serve as a solid starting point to investigate the role of anti-Sema4D therapy in tumor metastasis. Further in vivo studies are strongly encouraged to clinically determine their effects.