• 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 Osteopontin in Prostate Cancer Progression

      Robertson, Brian W.; Chellaiah, Meenakshi A. (2009)
      Our research investigates the relationship between the local environment of bone and how it influences the proliferation and metastasis of prostate cancer. Our focus centers on the bone extracellular matrix protein Osteopontin (OPN), which has previously been demonstrated to be an autocrine motility factor secreted by both osteoclasts and osteoblasts. In order to investigate the role of OPN in prostate cancer progression, we primarily employ PC3 prostate cancer cells derived from bony metastasis, but also look at the role of OPN in DU145 prostate cancer cells, and the lowly tumorigenic prostate cancer cell line LNCaP. OPN has been shown to activate Akt, and here we thoroughly define the OPN induced Akt cell survival pathway. Investigating the downstream players of activated Akt, we show that OPN induces an Akt-mediated increase in β-Catenin. Here we reveal a novel role for OPN, in inducing increased transcription of the TCF/LEF family of genes, of which β-catenin enhances as a co-factor after nuclear import. In an effort to more fully understand the role of OPN in prostate cancer progression, we investigated its role in MAPK signaling. Over-expression of OPN in PC3 cells resulted in the induced activation of the Erk1/2 pathway. Recently the field has determined that the metastatic potential of tumors or cancer cell lines can be measured through the scope of an Epithelial to Mesenchymal Transition(EMT). An EMT is typically characterized by a loss of E-Cadherin, an increase in N-Cadherin, and an increase in Vimentin. In order to more fully characterize the role of OPN in prostate cancer cell motility and metastasis, we probed the levels of EMT associated proteins. Surprisingly we found that OPN induces the opposite of an MET, a Mesenchymal to Epithelial Transition (MET), which is characterized by a more epithelial phenotype. Our results demonstrate that OPN can play many roles in prostate cancer progression, OPN increases survival of prostate cancer cells, OPN increases the expression of proteins important for cancer progression, and OPN helps to provide a means in which cancerous cells can aggregate and colonize a site of distant metastasis.