Nadia Coltella

MET Overexpression Turns Human Primary Osteoblasts into Osteosarcomas

The MET oncogene was causally involved in the pathogenesis of a rare tumor, i.e., the papillary renal cell carcinoma, in which activating mutations, either germline or somatic, were identified. MET activating mutations are rarely found in other human tumors, whereas at higher frequencies, MET is amplified and/or overexpressed in sporadic tumors of specific histotypes, including osteosarcoma. In this work, we provide experimental evidence that overexpression of the MET oncogene causes and sustains the full-blown transformation of osteoblasts. Overexpression of MET, obtained by lentiviral vector-mediated gene transfer, resulted in the conversion of primary human osteoblasts into osteosarcoma cells, displaying the transformed phenotype in vitro and the distinguishing features of human osteosarcomas in vivo. These included atypical nuclei, aberrant mitoses, production of alkaline phosphatase, secretion of osteoid extracellular matrix, and striking neovascularization. Although with a lower tumorigenicity, this phenotype was superimposable to that observed after transfer of the MET gene activated by mutation. Both transformation and tumorigenesis were fully abrogated when MET expression was quenched by short-hairpin RNA or when signaling was impaired by a dominant-negative MET receptor. These data show that MET overexpression is oncogenic and that it is essential for the maintenance of the cancer phenotype.

Role of the MET/HGF receptor in proliferation and invasive behavior of osteosarcoma

Signal transduction downstream HGF receptor (MET) activation involves multiple pathways that account for mitogenesis, motility and morphogenesis in a cell type‐dependent fashion. MET receptor is aberrantly expressed in almost 100% of human osteosarcomas. We analyzed the effect of the MET receptor activation in five human osteosarcoma cell lines evaluating the levels of HGF‐dependent activation of MAPK and PKB/AKT as biochemical readouts of mitogenic and invasive responses, respectively. All the cell lines tested expressed high levels of the MET proto‐oncogene. Four cell lines showed activation of the MAPK cascade upon HGF stimulation, suggesting that this growth factor serves a common proliferative function in osteosarcomas. Two lines showed activation of PKB/AKT, that is known to be involved in migration mediated by HGF receptor. Accordingly, cell lines where MAPK cascade was activated responded to HGF with increased proliferation, while induction and inhibition of PKB/AKT activity corresponded to acquisition or block of the invasive‐motile response to HGF, respectively. Both the HGF dependent responses were reverted by the specific MET inhibitor K252a. These data show that HGF activates both the mitogen and motogen machinery in osteosarcoma cells and suggest that HGF might promote their malignant behavior by concomitant activation of different pathways and biological functions.

The Therapeutic Potential of Hepatocyte Growth Factor to Sensitize Ovarian Cancer Cells to Cisplatin and Paclitaxel In vivo

Purpose: Advanced ovarian cancers are initially responsive to combinatorial chemotherapy with platinum drugs and taxanes but, in most cases, develop drug resistance. We recently showed that, in vitro, hepatocyte growth factor (HGF) enhances death of human ovarian cancer cell lines treated with cisplatin (CDDP) and paclitaxel. The present study addresses whether in vivo HGF makes ovarian carcinoma cells more responsive to these chemotherapeutics. Experimental Design: Using Lentiviral vectors carrying the HGF transgene, we transduced SK-OV-3 and NIH:OVCAR-3 ovarian carcinoma cell lines to obtain stable autocrine and paracrine HGF receptor activation. In vitro, we assayed growth, motility, invasiveness, and the response to CDDP and paclitaxel of the HGF-secreting bulk unselected cell populations. In vivo, we tested the cytotoxic effects of the drugs versus s.c. tumors formed by the wild-type and HGF-secreting cells in immunocompromised mice. Tumor-bearing mice were treated with CDDP (i.p.) and paclitaxel (i.v.), combined in different schedules and doses. Results:In vitro, HGF-secreting cells did not show altered proliferation rates and survival but were strongly sensitized to the death triggered by CDDP and paclitaxel, alone or in combination. In vivo, we found a therapeutic window in which autocrine/paracrine HGF made tumors sensitive to low doses of the drugs, which were ineffective on their own. Conclusions: These data provide the proof-of-concept that in vivo gene therapy with HGF might be competent in sensitizing ovarian cancer cells to conventional chemotherapy.

HIF-1α regulates the interaction of chronic lymphocytic leukemia cells with the tumor microenvironment

Hypoxia-inducible transcription factors (HIFs) regulate a wide array of adaptive responses to hypoxia and are often activated in solid tumors and hematologic malignancies due to intratumoral hypoxia and emerging new layers of regulation. We found that in chronic lymphocytic leukemia (CLL), HIF-1α is a novel regulator of the interaction of CLL cells with protective leukemia microenvironments and, in turn, is regulated by this interaction in a positive feedback loop that promotes leukemia survival and propagation. Through unbiased microarray analysis, we found that in CLL cells, HIF-1α regulates the expression of important chemokine receptors and cell adhesion molecules that control the interaction of leukemic cells with bone marrow and spleen microenvironments. Inactivation of HIF-1α impairs chemotaxis and cell adhesion to stroma, reduces bone marrow and spleen colonization in xenograft and allograft CLL mouse models, and prolongs survival in mice. Of interest, we found that in CLL cells, HIF-1α is transcriptionally regulated after coculture with stromal cells. Furthermore, HIF-1α messenger RNA levels vary significantly within CLL patients and correlate with the expression of HIF-1α target genes, including CXCR4, thus further emphasizing the relevance of HIF-1α expression to CLL pathogenesis.

Genes regulated by hepatocyte growth factor as targets to sensitize ovarian cancer cells to cisplatin

Advanced ovarian cancers are initially responsive to chemotherapy with platinum drugs but develop drug resistance in most cases. We showed recently that hepatocyte growth factor (HGF) enhances death of human ovarian cancer cell lines treated with cisplatin (CDDP) and that this effect is mediated by the p38 mitogen-activated protein kinase. In this work, we integrated genome-wide expression profiling, in silico data survey, and functional assays to identify transcripts regulated in SK-OV-3 ovarian cancer cells made more responsive to CDDP by HGF. Using oligonucleotide microarrays, we found that HGF pretreatment changes the transcriptional response to CDDP. Quantitative reverse transcription-PCR not only validated all the 15 most differentially expressed genes but also confirmed that they were primarily modulated by the combined treatment with HGF and CDDP and reversed by suppressing p38 mitogen-activated protein kinase activity. Among the differentially expressed genes, we focused functional analysis on two regulatory subunits of the protein phosphatase 2A, which were down-modulated by HGF plus CDDP. Decrease of each subunit by RNA interference made ovarian cancer cells more responsive to CDDP, mimicking the effect of HGF. In conclusion, we show that HGF and CDDP modulate transcription in ovarian cancer cells and that this transcriptional response is involved in apoptosis regulation. We also provide the proof-of-concept that the identified genes might be targeted to either increase the efficacy of chemotherapeutics or revert chemotherapy resistance. [Mol Cancer Ther 2006;5(5):1126–35]

HIF factors cooperate with PML-RARα to promote acute promyelocytic leukemia progression and relapse

Acute promyelocytic leukemia (APL) is epitomized by the chromosomal translocation t(15;17) and the resulting oncogenic fusion protein PML‐RARα. Although acting primarily as a transcriptional repressor, PML‐RARα can also exert functions of transcriptional co‐activation. Here, we find that PML‐RARα stimulates transcription driven by HIF factors, which are critical regulators of adaptive responses to hypoxia and stem cell maintenance. Consistently, HIF‐related gene signatures are upregulated in leukemic promyelocytes from APL patients compared to normal promyelocytes. Through in vitro and in vivo studies, we find that PML‐RARα exploits a number of HIF‐1α‐regulated pro‐leukemogenic functions that include cell migration, bone marrow (BM) neo‐angiogenesis and self‐renewal of APL blasts. Furthermore, HIF‐1α levels increase upon treatment of APL cells with all‐trans retinoic acid (ATRA). As a consequence, inhibiting HIF‐1α in APL mouse models delays leukemia progression and exquisitely synergizes with ATRA to eliminate leukemia‐initiating cells (LICs).

Pml Represses Tumour Progression Through Inhibition of mTOR

The promyelocytic leukaemia gene PML is a pleiotropic tumour suppressor. We have recently demonstrated that PML opposes mTOR‐HIF1α‐VEGF signalling in hypoxia. To determine the relevance of PML‐mTOR antagonism in tumourigenesis, we have intercrossed Pml null mice with Tsc2 heterozygous mice, which develop kidney cysts and carcinomas exhibiting mTOR upregulation. We find that combined inactivation of Pml and Tsc2 results in aberrant TORC1 activity both in pre‐tumoural kidneys as well as in kidney lesions. Such increase correlates with a marked acceleration in tumour progression, impacting on both the biology and histology of kidney carcinomas. Also, Pml inactivation decreases the rate of loss of heterozygosity (LOH) for the wt Tsc2 allele. Interestingly, however, aberrant TORC1 activity does not accelerate renal cystogenesis in Tsc2/Pml mutants. Our data demonstrate that activation of mTOR is critical for tumour progression, but not for tumour initiation in the kidney.

Bone Marrow Endosteal Mesenchymal Progenitors Depend on HIF Factors for Maintenance and Regulation of Hematopoiesis

Summary Maintenance and differentiation of hematopoietic stem cells (HSCs) is regulated through cell-autonomous and non-cell-autonomous mechanisms within specialized bone marrow microenvironments. Recent evidence demonstrates that signaling by HIF-1α contributes to cell-autonomous regulation of HSC maintenance. By investigating the role of HIF factors in bone marrow mesenchymal progenitors, we found that murine endosteal mesenchymal progenitors express high levels of HIF-1α and HIF-2α and proliferate preferentially in hypoxic conditions ex vivo. Inactivation of either HIF-1α or HIF-2α dramatically affects their phenotype, propagation, and differentiation. Also, downregulation of HIF factors provokes an increase in interferon-responsive genes and triggers expansion and differentiation of hematopoietic progenitors by a STAT1-mediated mechanism. Interestingly, in conditions of demand-driven hematopoiesis HIF factors are specifically downregulated in mesenchymal progenitors in vivo. In conclusion, our findings indicate that HIF factors also regulate hematopoiesis non-cell-autonomously by preventing activation of a latent program in mesenchymal progenitors that promotes hematopoiesis.

Fumarase tumor suppressor gene and MET oncogene cooperate in upholding transformation and tumorigenesis

Loss of the fumarate hydratase (FH) tumor suppressor gene results in the development of benign tumors that rarely, but regrettably, progress to very aggressive cancers. Using mouse embryo fibroblasts (MEFs) to model transformation, we found that fh knockdown results in increased expression of the met oncogene‐encoded tyrosine kinase receptor through hypoxia‐inducible factor (hif) stabilization. MET‐in‐creased expression was alone able to stabilize hif, thus establishing a feed forward loop that might enforce tumor progression. The fh‐defective MEFs showed increased motility and protection from apoptosis. Motility, but not survival, relied on hif‐1α and was greatly enhanced by MET ligand hepatocyte growth factor. Met cooperated with a weakly oncogenic ras in making MEFs transformed and tumorigenic, as shown by in vitro and in vivo assays. Loss of fh was not equally effective by itself but enhanced the transformed and tumorigenic phenotype induced by ras and MET. Consistently, the rescue of fumarase expression abrogated the motogenic and transformed phenotype of fh‐defective MEFs. In conclusion, the data suggest that the progression of tumors where FH is lost might be boosted by activation of the MET oncogene, which is able to drive cell‐autonomous tumor progression and is a strong candidate for targeted therapy.—Costa, B., Dettori, D., Lorenzato, A., Bardella, C., Coltella, N., Martino, C., Cammarata, C., Carmeliet, P., Olivero, M., Di Renzo, M. F. Fumarase tumor suppressor gene and MET oncogene cooperate in upholding transformation and tumorigenesis. FASEB J. 24, 2680–2688 (2010). www.fasebj.org

PML promotes metastasis of triple-negative breast cancer through transcriptional regulation of HIF1A target genes

Elucidating the molecular basis of tumor metastasis is pivotal for eradicating cancer-related mortality. Triple-negative breast cancer (TNBC) encompasses a class of aggressive tumors characterized by high rates of recurrence and metastasis, as well as poor overall survival. Here, we find that the promyelocytic leukemia protein PML exerts a prometastatic function in TNBC that can be targeted by arsenic trioxide. We found that, in TNBC patients, constitutive HIF1A activity induces high expression of PML, along with a number of HIF1A target genes that promote metastasis at multiple levels. Intriguingly, PML controls the expression of these genes by binding to their regulatory regions along with HIF1A. This mechanism is specific to TNBC cells and does not occur in other subtypes of breast cancer where PML and prometastatic HIF1A target genes are underexpressed. As a consequence, PML promotes cell migration, invasion, and metastasis in TNBC cell and mouse models. Notably, pharmacological inhibition of PML with arsenic trioxide, a PML-degrading agent used to treat promyelocytic leukemia patients, delays tumor growth, impairs TNBC metastasis, and cooperates with chemotherapy by preventing metastatic dissemination. In conclusion, we report identification of a prometastatic pathway in TNBC and suggest clinical development toward the use of arsenic trioxide for TNBC patients.