The emerging role of MMP14 in brain tumorigenesis and future therapeutics

Glioblastoma is a malignant brain tumor of glial origin. These tumors are thought to be derived from astrocytic cells that undergo malignant transformation. A growing body of evidence suggests that upregulation of MMP expression plays a significant role in promoting glioma pathogenesis. Elevated expression of MMP14 not only promotes glioma invasion and tumor cell proliferation but also plays a role in angiogenesis. Despite the fact that levels of MMP14 correlate with breast cancer progression, the controversial role of MMP14 in gliomagenesis needs to be elucidated. In the present review, we discuss the role of MMP14 in glioma progression as well as the mechanisms of MMP14 regulation in the context of future therapeutic manipulations.     

Role of hyaluronan in glioma invasion

Gliomas are the most common primary intracranial tumors. Their distinct ability to infiltrate into the extracellular matrix (ECM) of the brain makes it impossible to treat these tumors using surgery and radiation therapy. A number of different studies have suggested that hyaluronan (HA), the principal glycosaminoglycan (GAG) in the ECM of the brain, is the critical factor for glioma invasion. HA-induced glioma invasion was driven by two important molecular events: matrix metalloproteinase (MMP) secretion and upregulation of cell migration. MMP secretion was triggered by HA-induced focal adhesion kinase (FAK) activation, which transmits its signal through ERK activation and nuclear factor kappa B (NFκB) translocation. Another important molecular event is osteopontin (OPN) expression. OPN expression by AKT activation triggers cell migration. These results suggest that HA-induced glioma invasion is tightly regulated by signaling mechanisms, and a detailed understanding of this molecular mechanism will provide important clues for glioma treatment.Key words: hyaluronan, matrix metalloproteinase, osteopontin, emodin, invasion, gliomaMalignant gliomas are highly invasive and infiltrative tumors that have a poor prognosis with a median survival of only one year.^1,2 A major barrier to effective malignant glioma treatment is the invasion of these cells into brain parenchyma. Because of this fact, local therapies such as surgery or radiation therapy are not effective.³ Glioma cells invade through the ECM of the brain by activating a number of coordinated cellular programs, which include those necessary for migration and invasion.³ Therefore, a detailed understanding of the mechanisms underlying this invasive behavior is essential for the development of novel effective therapies.During glioma invasion, tumor cells closely interact with the ECM. Although brain tumor cells may share some of the invasive characteristics with tumors that arise outside of the central nerve system (CNS), the particular structure and composition of the brain ECM suggest the existence of unique invasive mechanisms for brain tumors.⁴Brain ECM is composed of typical ECM proteins and a HA scaffold with associated glycoproteins and proteoglycans.⁵ Typical ECM proteins such as laminin, type-IV collagen and fibronectin have been implicated in the invasion of other tumors by regulating cell adhesion and migration.⁶ However HA, which is associated with proteoglycans and GAGs, is especially abundant in the brain parenchyma compared to other tissues.⁷ Furthermore, malignant gliomas contain higher amounts of HA than normal brain tissue.⁷ These facts raise the possibility that HA might play an important role in glioma invasion, a process that is distinct from other non-CNS derived tumors.     

Microregional extracellular matrix heterogeneity in brain modulates glioma cell invasion

The invasion of neoplastic cells into healthy brain tissue is a pathologic hallmark of gliomas and contributes to the failure of current therapeutic modalities (surgery, radiation and chemotherapy). Transformed glial cells share the common attributes of the invasion process, including cell adhesion to extracellular matrix (ECM) components, cell locomotion, and the ability to remodel extracellular space. However, glioma cells have the ability to invade as single cells through the unique environment of the normal central nervous system (CNS). The brain parenchyma has a unique composition, mainly hyaluronan and is devoid of rigid protein barriers composed of collagen, fibronectin and laminin. The integrins and the hyaluronan receptor CD44 are specific adhesion receptors active in glioma-ECM adhesion. These adhesion molecules play a major role in glioma cell-matrix interactions because the neoplastic cells use these receptors to adhere to and migrate along the components of the brain ECM. They also interact with the proteases secreted during glioma progression that degrade ECM allowing tumor cells to spread and diffusely infiltrate the brain parenchyma. The plasminogen activators (PAs), matrix metalloproteinases (MMPs) and lysosomal cysteine peptidases called cathepsins are also induced during the invasive process. Understanding the mechanisms of tumor cell invasion is critical as it plays a central role in glioma progression and failure of current treatment due to tumor recurrence from micro-disseminated disease. This review will focus on the impact of microregional heterogeneity of the ECM on glioma invasion in the normal adult brain and its modifications in tumoral brain.     

Human Cytomegalovirus Gene Expression in Long-Term Infected Glioma Stem Cells

The most common adult primary brain tumor, glioblastoma (GBM), is characterized by fifteen months median patient survival and has no clear etiology. We and others have identified the presence of human cytomegalovirus (HCMV) gene products endogenously expressed in GBM tissue and primary cells, with a subset of viral genes being consistently expressed in most samples. Among these viral genes, several have important oncomodulatory properties, regulating tumor stemness, proliferation, immune evasion, invasion and angiogenesis. These findings lead us to hypothesize that a specific HCMV gene signature may be associated with GBM pathogenesis. To investigate this hypothesis, we used glioma cell lines and primary glioma stem-like cells (GSC) infected with clinical and laboratory HCMV strains and measured relative viral gene expression levels along several time points up to 15 weeks post-infection. While HCMV gene expression was detected in several infected glioma lines through week 5 post-infection, only HCMV-infected GSC expressed viral gene products 15 weeks post-infection. Efficiency of infection across time was higher in GSC compared to cell lines. Importantly, HCMV-infected GSC outlived their uninfected counterparts, and this extended survival was paralleled by increased tumorsphere frequency and upregulation of stemness regulators, such as SOX2, p-STAT3, and BMX (a novel HCMV target identified in this study). Interleukin 6 (IL-6) treatment significantly upregulated HCMV gene expression in long-term infected glioma cultures, suggesting that pro-inflammatory signaling in the tumor milieu may further augment HCMV gene expression and subsequent tumor progression driven by viral-induced cellular signaling. Together, our data support a critical role for long-term, low-level HCMV infection in promoting survival, stemness, and proliferation of GSC that could significantly contribute to GBM pathogenesis.     

c‐Cbl regulates glioma invasion through matrix metalloproteinase 2

c‐Cbl, a multifunctional adaptor and an E3 ubiquitin ligase, plays a role in such cytoskeleton‐mediated events as cell adhesion and migration. Invasiveness of human glioma is dependent on cell adhesion, migration, and degradation of extracellular matrix (ECM). However, the function of c‐Cbl in glioma invasion has never been investigated. We report here, for the first time, that c‐Cbl plays a positive role in the invasion of ECM by SNB19 glioma cells. RNAi‐mediated depletion of c‐Cbl decreases SNB19 cell invasion and expression of matrix metalloproteinase 2 (MMP2). Consistent with these findings, SNB19 cells expressing wild‐type, but not mutant c‐Cbl show increased invasion and MMP2 expression. We demonstrate that the observed role of c‐Cbl in invasion of SNB19 cells is not mediated by the previously shown effects of c‐Cbl on cell adhesion and migration or on EGFR signaling. Together, our results suggest that c‐Cbl promotes glioma invasion through up‐regulation of MMP2. J. Cell. Biochem. 111: 1169–1178, 2010. © 2010 Wiley‐Liss, Inc.     

CD44 adhesion molecule and neuro-glial proteoglycan NG2 as invasive markers of glioma

Glioma invasion into the CNS involves the interaction of tumor cells with the host’s cells and extracellular matrix (ECM) molecules. In this study, the expression of ECM-associated and cell-associated proteins such as the transmembrane CD44 adhesion molecule and neuro-glial proteoglycan 2 (NG2), a member of the chondroitin sulfate proteoglycan family, were evaluated during glioma progression, in vitro and in vivo, using a model of a highly invasive and aggressive intracerebral mouse G-26 glioma. We found a marked increase in CD44 and NG2 expression in brain tissue containing glioma. The glioma levels of these proteins gradually increased over time to reach 3–15 times the levels in the contralateral control. NG2 and CD44 expression paralleled progression of the glioma, being higher on days 14 and 21 than on day 2 post-glioma implant. In addition, when invading glioma crossed the midline in the advanced tumor stage, levels of each of these proteins in the contralateral tissue were elevated, but were still significantly lower than in the ipsilateral, tumor-bearing hemisphere. Immunohistochemistry of advanced stage G-26 glioma (day 21) showed CD44 expression to be most prominent at the front of the glioma invasion line, sharply separated from normal brain parenchyma which expressed glial fibrillary acidic protein (GFAP). However, single CD44 positive cells that escaped the tumor mass penetrated between the astrocytes that encased the tumor at its periphery. In contrast, NG2 was expressed on nearly all glioma cells within the tumor mass but less so at the leading edge of the tumor. The NG2 positive cells were clearly demarcated and morphologically distinguishable from GFAP positive cells and only sporadic, small groups of NG2 positive cells were seen in the GFAP positive zone of the neuropil. Taken together, these data show that during glioma progression in the brain, the level and pattern of glioma-associated molecules such as CD44 and NG2 may aid in tracing and targeting the invading glioma cells.     

Recombinant CBD-HepII polypeptide of fibronectin inhibits alphavbeta3 signaling and hematogenous metastasis of tumor

The interaction of integrin αvβ3 and its ligands are crucial for tumor metastasis. Recombinant CBD-HepII polypeptide of fibronectin, designated as CH50, suppressed the binding of tumor cells to ECM molecules, and abolished the promoting effect of soluble fibronectin and fibrinogen on tumor cell adhesion to ECM molecules. The underlying mechanisms involve the blockade and downregulation of αvβ3 and its co-receptor syndecan 1 by CH50. The activation of FAK, upregulation of cdc2, the production and activation of MMP-2 and MMP-9 by ECM molecules-stimulated tumor cells were inhibited by CH50. CH50 reduced the tumor cell arrest during blood flow, and also inhibited the invasive ability of tumor cells. The in vivo expressed CH50 suppressed the lung metastasis of circulating tumor cells, and prolonged the survival of mice after tumor cell inoculation. These findings suggest a prospective utility of CH50 in the gene therapy for prevention of tumor metastasis.     

Long noncoding RNA FOXD2-AS1 promotes glioma malignancy and tumorigenesis via targeting miR-185-5p/CCND2 axis

Glioma is the most aggressive malignant tumor in the adult central nervous system. Abnormal long noncoding RNA (lncRNA) FOXD2-AS1 expression was associated with tumor development. However, the possible role of FOXD2-AS1 in the progression of glioma is not known. In the present study, we used in vitro and in vivo assays to investigate the effect of abnormal expression of FOXD2-AS1 on glioma progression and to explore the mechanisms. FOXD2-AS1 was upregulated in glioma tissue, cells, and sphere subpopulation. Upregulation of FOXD2-AS1 was correlated with poor prognosis of glioma. Downregulation of FOXD2-AS1 decreased cell proliferation, migration, invasion, stemness, and epithelial-mesenchymal transition (EMT) in glioma cells and inhibited tumor growth in transplanted tumor. We also revealed that FOXD2-AS1 was mainly located in cytoplasm and microRNA (miR)-185-5p both targeted FOXD2-AS1 and CCND2 messenger RNA (mRNA) 3′-untranslated region (3′-UTR). miR-185-5p was downregulated in glioma tissue, cells, and sphere subpopulation. Downregulation of miR-185-5p was closely correlated with poor prognosis of glioma patients. In addition, miR-185-5p mimics decreased cell proliferation, migration, invasion, stemness, and EMT in glioma cells. CCND2 was upregulated in glioma tissue, cells, and sphere subpopulation. Upregulation of CCND2 was closely correlated with poor prognosis of glioma patients. CCND2 knockdown decreased cell proliferation, migration, invasion, and EMT in glioma cells. In glioma tissues, CCND2 expression was negatively associated with miR-185-5p, but positively correlated with FOXD2-AS1. FOXD2-AS1 knockdown and miR-185-5p mimics decreased CCND2 expression. Inhibition of miR-185-5p suppressed FOXD2-AS1 knockdown-induced decrease of CCND2 expression. Overexpression of CCND2 suppressed FOXD2-AS1 knockdown-induced inhibition of glioma malignancy. Taken together, our findings highlight the FOXD2-AS1/miR-185-5p/CCND2 axis in the glioma development.     

IRF2-ferroptosis related gene is associated with prognosis and EMT in gliomas

Ferroptosis is a new type of programmed cell death that has excellent anti-tumor potential in different tumors. However, the research on ferroptosis in glioma is still incomplete. In this study, we aimed to revealed the relationship between ferroptosis-related genes (FRGs) and glioma. We collected gene expression profiles of glioma patients from the TCGA and CGGA databases. All glioma samples were classified into five subtypes using the R software ConsensusClusterPlus. Subsequently, we performed single sample gene set enrichment analysis (ssGSEA) to explore the correlation between different subtypes and immune status and ferroptosis. Then co-expression modules were constructed via weighted gene co-expression network analysis (WGCNA). A Gene Ontology (GO) analysis was conducted to analyze the potential biological functions of the genes in the modules. Finally, we identified 10 hub genes using the PPI network. The in vitro experiments were used to validate our predictions. We found that the expression level of IRF2 is positively correlated with the grade of glioma. The overexpression of IRF2 could protect glioma cells from ferroptosis and enhance the invasive and migratory abilities. Silence of IRF2 had the opposite effect. In conclusion, we demonstrated a novel ferroptosis-related signature for predicting prognosis, and IRF2 could be a potential biomarker for diagnosis and treatment in glioma.     

PTH-related protein enhances LoVo colon cancer cell proliferation, adhesion, and integrin expression

Parathyroid hormone-related protein (PTHrP) has been localized in human colon cancer tissue and cell lines. Tumor cell adhesion to extracellular matrix (ECM) proteins plays a major role in the invasion and metastasis of tumor cells, and is mediated via integrin subunits. The LoVo human colon cancer cell line was used as a model system to study the effects of PTHrP on cell proliferation and adhesion to ECM proteins found in normal liver. Clones of LoVo cells engineered to overexpress PTHrP by stable transfection with a PTHrP cDNA showed enhanced cell proliferation vs. control (empty vector-transfected) cells. PTHrP-overexpressing cells also showed significantly higher adhesion to collagen type I, fibronectin, and laminin, and enhanced expression of the [symbol: see text] integrin subunits. These results indicate that PTHrP may play a role in colon cancer invasion and metastasis by increasing cell proliferation and adhesion to the ECM via upregulation of proinvasive integrin expression.     

Osteopontin stimulates tumor growth and activation of promatrix metalloproteinase-2 through nuclear factor-kappa B-mediated induction of membrane type 1 matrix metalloproteinase in murine melanoma cells

Matrix metalloproteinases (MMPs) degrade the extracellular matrix (ECM) and play critical roles in tissue repair, tumor invasion, and metastasis. MMPs are regulated by different cytokines, ECM proteins, and other factors. However, the molecular mechanisms by which osteopontin (OPN), an ECM protein, regulates ECM invasion and tumor growth and modulates MMP activation in B16F10 cells are not well defined. We have purified OPN from human milk and shown that OPN induces pro-MMP-2 production and activation in these cells. Moreover, our data revealed that OPN-induced membrane type 1 (MT1) MMP expression correlates with translocation of p65 (nuclear factor-kappaB (NF-kappaB)) into the nucleus. However, when the super-repressor form of IkappaBalpha (inhibitor of NF-kappaB) was transfected into cells followed by treatment with OPN, no induction of MT1-MMP expression was observed, indicating that OPN activates pro-MMP-2 via an NF-kappaB-mediated pathway. OPN also enhanced cell migration and ECM invasion by interacting with alpha(v)beta(3) integrin, but these effects were reduced drastically when the MMP-2-specific antisense S-oligonucleotide was used to suppress MMP-2 expression. Interestingly, when the OPN-treated cells were injected into nude mice, the mice developed larger tumors, and the MMP-2 levels in the tumors were significantly higher than in controls. The proliferation data indicate that OPN increases the growth rate in these cells. Both tumor size and MMP-2 expression were reduced dramatically when anti-MMP-2 antibody or antisense S-oligonucleotide-transfected cells were injected into the nude mice. To our knowledge, this is the first report that MMP-2 plays a direct role in OPN-induced cell migration, invasion, and tumor growth and that demonstrates that OPN-stimulated MMP-2 activation occurs through NF-kappaB-mediated induction of MT1-MMP.     

TGF-β promotes glioma cell growth via activating Nodal expression through Smad and ERK1/2 pathways

While there were certain studies focusing on the mechanism of TGF-β promoting the growth of glioma cells, the present work revealed another novel mechanism that TGF-β may promote glioma cell growth via enhancing Nodal expression. Our results showed that Nodal expression was significantly upregulated in glioma cells when TGF-β was added, whereas the TGF-β-induced Nodal expression was evidently inhibited by transfection Smad2 or Smad3 siRNAs, and the suppression was especially significant when the Smad3 was downregulated. Another, the attenuation of TGF-β-induced Nodal expression was observed with blockade of the ERK1/2 pathway also. Further detection of the proliferation, apoptosis, and invasion of glioma cells indicated that Nodal overexpression promoted the proliferation and invasion of tumor cells and inhibited their apoptosis, resembling the effect of TGF-β addition. Downregulation of Nodal expression via transfection Nodal-specific siRNA in the presence of TGF-β weakened the promoting effect of the latter on glioma cells growth, and transfecting Nodal siRNA alone in the absence of exogenous TGF-β more profoundly inhibited the growth of glioma cells. These results demonstrated that while both TGF-β and Nodal promoted glioma cells growth, the former might exert such effect by enhancing Nodal expression, which may form a new target for glioma therapy.     

ZEB1上调神经细胞黏附分子促进胶质瘤细胞侵袭与转移

胶质瘤是一种较为常见的颅内恶性肿瘤,其侵袭转移能力强,影响临床疗效。探讨胶质瘤发生侵袭转移的分子机制,寻找新的靶点干预胶质瘤侵袭转移是目前亟待解决的重大课题。我们前期研究中发现,神经细胞黏附分子（neuronal cell adhesion molecule, NRCAM）在各种胶质瘤细胞中的表达量均显著高于其在人正常星形胶质细胞(NHA)中的表达量（NRCAM在胶质瘤A172和T98G中的表达量分别是其在NHA中的2.15和17.63倍）;且根据人类蛋白质组学数据库信息及qRT-PCR结果证实,NRCAM在胶质瘤组织中的表达量也显著高于其在正常组织中的表达。Kaplan-Meier分析提示,高表达的NRCAM与胶质瘤患者较差的预后正相关。在此基础上,通过生物信息学预测的方法结合双荧光素酶报告基因实验证实,转录因子锌指E盒结合蛋白1(ZEB1)能够增加NRCAM启动子活性,上调NRCAM mRNA和蛋白质水平的表达量。通过Transwell实验证实,在过表达ZEB1的胶质瘤细胞A172中,沉默NRCAM将抑制该细胞的侵袭能力。而在敲低ZEB1的胶质瘤细胞T98G中,过表达NRCAM将增加该细胞的侵袭能力。总之,NRCAM在胶质瘤中显著高表达且与患者较差的预后正相关。ZEB1转录上调NRCAM来增加胶质瘤细胞侵袭能力。     

Regulation of human trophoblast migration and invasiveness

The human placenta is an invasive structure in which highly proliferative, migratory, and invasive extravillous trophoblast (EVT) cells migrate and invade the uterus and its vasculature. Using in vitro propagated normal first-trimester EVT cells and immortalized EVT cells, which share all of the phenotypic and functional characteristics of the normal EVT cells, it has been shown that migration/invasion of human EVT cells is stringently regulated by many growth factors, their binding proteins, extracellular matrix (ECM) components, and some adhesion molecules in an autocrine/paracrine manner at the fetal-maternal interface in human pregnancy. Transforming growth factor beta (TGF-beta), decorin (a proteoglycan in the ECM), and melanoma cell adhesion molecule (Mel-CAM) inhibit, and insulin-like growth factor II (IGF-II), IGF-binding protein 1 (IGFBP-1), and endothelin 1 (ET-1) stimulate EVT cell migration/invasion. Inhibition of EVT cell migration by TGF-beta has been suggested to be due to upregulation of integrins, which make the cells more adhesive to the ECM. Its antiinvasive action is due to an upregulation of tissue inhibitor of matrix metalloprotease 1 (TIMP-1) and plasminogen activator inhibitor (PAI-1) and a downregulation of urokinase-type plasminogen activator (uPA). Molecular mechanisms of inhibition of migration/invasion of EVT cells by decorin and Mel-CAM remain to be identified. IGF-II action has been shown to be mediated by IGF type I receptors (IGF-RII) independently of IGF type I receptors (IGF-RI) and IGFBPs. This action of IGF-II appears to involve inhibitory G proteins and phosphorylation of mitogen-activated protein kinase (MAPK) (extracellular signal-regulated protein kinases 1 and 2 (ERK-1 and ERK-2)). IGFBP-1 stimulation of EVT cell migration appears to occur by binding its Arg-Gly-Asp (RGD) domain to alpha5beta1 integrin, leading to phosphorylation of focal adhesion kinase (FAK) and MAPK (ERK-1 and ERK-2). These studies may improve our understanding of diseases related to abnormal placentation, viz. hypoinvasiveness in preeclampsia and hyperinvasiveness in trophoblastic neoplasms.     

Chromosomal aberration arises during somatic reprogramming to pluripotent stem cells

Recurrence of Glioblastoma multiforme (GBM) seems to be the rule despite combination therapies. Cell invasion and cell proliferation are major reasons for recurrence of GBM. And insulin-like growth factor binding protein 5 (IGFBP5) is the most conserved of the IGFBPs and is frequently dysregulated in cancers and metastatic tissues. By studying the human glioma tissues, we find that IGFBP5 expression associate to the histopathological classification and highly expressed in GBM. Using IGFBP5 mutants we demonstrate that knockdown of IGFBP5 inhibited cell invasion, whereas promoting cell proliferation in GBM cells. Mechanistically, we observed that promoting GBM cell proliferation by inhibiting IGFBP5 was associated with stimulating Akt (Protein kinase B) phosphorylation. However, IGFBP5 promote GBM cell invasion was related to the epithelial-to-mesenchymal transition (EMT). Furthermore, the Chinese Glioma Genome Altas (CGGA) database show that IGFBP5 is significantly increased in recurrent glioma and it predicted worse survival. The obtained results indicate that IGFBP5 has two sides in GBM—inhibiting cell proliferation but promoting cell invasion.     

Numbl inhibits glioma cell migration and invasion by suppressing TRAF5-mediated NF-κB activation

The Notch signaling regulator Numblike (Numbl) is expressed in the brain, but little is known regarding its role in the pathophysiology of glial cells. In this paper, we report that Numbl expression was down-regulated in high-grade human glioma tissue samples and glioblastoma cell lines. To investigate the role of Numbl in glioma migration and invasion, we generated human glioma cell lines in which Numbl was either overexpressed or depleted. Overexpression of Numbl suppressed, while elimination of Numbl promoted, the migration and invasion of glioma cells. Numbl inhibited glioma migration and invasion by dampening NF-κB activity. Furthermore, Numbl interacted directly with tumor necrosis factor receptor-associated factor 5 (TRAF5), which signals upstream and is required for the activation of NF-κB, and committed it to proteasomal degradation by promoting K48-linked polyubiquitination of TRAF5. In conclusion, our data suggest that Numbl negative regulates glioma cell migration and invasion by abrogating TRAF5-induced activation of NF-κB.     

Parathyroid hormone-related protein upregulates integrin expression via an intracrine pathway in PC-3 prostate cancer cells

Parathyroid hormone-related protein (PTHrP) is expressed by human prostatic tissue and prostate cancer cell lines, and enhances prostate tumor cell growth both in vivo and in vitro. PTHrP expression also plays a role in the development of bone metastasis, which is a frequent complication in patients with prostate carcinoma. Tumor cell adhesion to extracellular matrix (ECM) components is mediated via integrin subunits, and plays a major role in the invasion and metastasis of tumor cells. We previously showed that PTHrP overexpression increases adhesion of the human prostate cancer cell line PC-3 to the ECM molecules collagen type I, fibronectin, and laminin. Increased adhesion is accompanied by upregulation in the expression of alpha1, alpha5, alpha6, and beta4 integrin subunits. We used the same cell line to study the mechanism via which PTHrP upregulates integrin expression. Clonal PC-3 cells were established overexpressing wild-type PTHrP or PTHrP mutated in the nuclear localization sequence (NLS). Mutation of the NLS negated the effects of PTHrP on alpha1, alpha5, alpha6, and beta4 integrin expression, indicating that these effects are mediated via an intracrine pathway requiring nuclear localization. Expression of the alpha2, alpha3, alphav, and beta1 integrin subunits were comparable in wild-type and NLS-mutated PTHrP transfectants. These findings indicate that PTHrP may play a role in prostate tumor invasion and metastasis by upregulating the expression of specific integrin subunits via an intracrine pathway.