Ribozyme‐targeting reveals the rate‐limiting role of pleiotrophin in glioblastoma

Abstract

Glioblastomas (GBMs) are the most frequent malignant brain tumors with very limited treatment options and nearly all GBM patients dying within 1 year. Pleiotrophin (PTN, HB-GAM, HBNF, OSF-1) is a secreted growth factor that shows mitogenic, chemotactic and transforming activity. While PTN expression is tightly regulated during embryogenesis and very limited in normal adult tissues, a marked PTN upregulation is seen in tumors including glioblastomas. Targeting of the PTN receptors, ALK and RPTP-zeta, indicates a contribution of PTN-activated signaling pathways in glioblastomas. However, the relevance of PTN expression itself is unknown especially since, besides PTN, at least one more growth factor, midkine (MK), signals through ALK and is expressed in glioblastoma. Here we demonstrate the biologic relevance of PTN in 2 glioblastoma cell lines in vitro and in vivo. We show that stable ribozyme-targeting leads to a robust reduction of PTN mRNA and protein levels. This results in decreased cell proliferation, cell migration and soft agar colony formation in vitro. Comparing clonal ribozyme-transfected cells with different residual PTN levels, we establish a PTN gene-dose effect of glioblastoma cell proliferation. In a subcutaneous tumor xenograft mouse model, in vivo growth is markedly reduced upon PTN depletion, which is paralleled by decreased PTN serum levels. Furthermore, the immunohistochemical analysis of the tumors shows reduced angiogenesis in PTN-depleted tumors. We conclude that PTN is a rate-limiting growth factor in glioblastoma. Since PTN is overexpressed in glioblastomas but rarely found in normal tissue, PTN may represent an attractive therapeutic target. ' 2005 Wiley-Liss, Inc.Key words: pleiotrophin; PTN; glioblastoma; ribozyme-targeting; tumor growth; tumor angiogenesis Gliomas are the most common primary CNS tumors in humans, which are subdivided according to the WHO into low-grade astrocytomas (grade 2), anaplastic astrocytomas (grade 3) and glioblastomas (GBMs; grade 4). Glioblastomas, which can arise de novo or progress from lower-grade gliomas, are the most frequent and most malignant brain tumors, with nearly all GBM patients dying within 1 year despite aggressive treatment.1 Clearly, an insight into the molecular basis of glioblastoma growth may provide new therapeutic strategies.Pleiotrophin (PTN), also referred to as heparin-binding growthassociated molecule (HB-GAM), heparin-binding growth factor 8, heparin-binding neurotrophic factor (HBNF), or osteoblast-specific protein-1 (OSF-1), is a 15.3 kDa secreted protein that was originally purified from human breast cancer cells, 2 bovine uterus, 3 as well as neonatal rat brain. 4,5 Based on its time-and tissuespecific expression pattern during rodent development, PTN represents a developmentally regulated cytokine whose expression gets increasingly restricted with progressing organ differentiation and drops after the perinatal phase. In the CNS, PTN expression is high in neuroepithelial progenitor cells as well as in glial cells and neurons du...

HARPΔ111-136 enhances radiation-induced apoptosis of U87MG glioblastoma by induction of the proapoptotic protein CHOP

“…These findings confirmed in vivo that the peptide HARPΔ111-136 sensitized U87MG cells to apoptosis. Discussion HARP has been described as a growth factor for several tumor types (3,15,33) and in a previous study using U87MG glioblastoma cell line as an experimental model, we demonstrated that the HARP inhibitor HARPΔ111-136 exerts antiproliferative and potent anti-angiogenic activities. The aim of the present study was to investigate the mechanism of HARPΔ111-136 biological action; a recombinant adenovirus was used to produce high levels of the inhibitor HARPΔ111-136 in the glioblastoma U87MG cell line.…”

“…Resistance to apoptosis is a well known feature of glioblastoma cells leading to a poor response to chemotherapy and radiation therapy (14). Since HARP has been considered as a growth and a survival factor for cancer cells (15,16), blocking the HARP pathway could be of particular interest.…”

Pleiotrophin, A Multifunctional Tumor Promoter Through Induction of Tumor Angiogenesis, Remodeling of the Tumor Microenvironment, and Activation of Stromal Fibroblasts

“…Of critical importance, different approaches to attenuate PTN's function in the tumor cells that in appropriately express Ptn was found to decrease tumor growth in vivo, thus constitutive PTN signaling is vital and a rate-limiting factor in the pathogenesis of these tumors. [50][51][52][53] …”

Anaplastic lymphoma kinase in human cancer

“…ALK receptor expression, originally documented in a variety of cancer lines, has been documented in many neuronal tumors , Miyake et al 2002, Stoica et al 2002, Osajima-Hakomori et al 2005, glioblastoma (Powers et al 2002, Shao et al 2002, Grzelinski et al 2005, Lu et al 2005, and mesenchymal neoplasms including melanoma (Dirks et al 2002) and rhabdomyosarcoma (Morris et al 1994, Falini et al 1998, Cessna et al 2002, Pillay et al 2002, Li et al 2004. In this context, ALK overexpression or gain of function mutations have been demonstrated to be tumorigenic.…”