Whole-body irradiation at the minimal lethal dose causes bone marrow failure and death within 12–18 days. To identify the principal components of the hematopoietic system that are radioprotective, we transplanted lethally irradiated mice with purified progenitors: common myeloid progenitors (CMPs), megakaryocyte/erythrocyte-restricted progenitors (MEPs), or granulocyte/monocyte-restricted progenitors (GMPs). Transplanted CMPs gave rise to cells both of the granulocyte/monocyte (GM) series and the megakaryocyte/erythrocyte series, whereas GMPs or MEPs showed reconstitution of only GM or ME cells, respectively. CMPs and MEPs but not GMPs protected mice in a dose-dependent manner, suggesting that erythrocytes, platelets, or both are the critical effectors of radioprotection. Accordingly, CMPs and MEPs formed robust colonies in recipient bone marrow and spleen, whereas GMPs formed small colonies that rapidly disappeared. Direct comparisons of spleen CFU (CFU-S) potentials among each progenitor subset showed that MEPs contain the vast majority of day 8 CFU-S activity, suggesting that day 8 CFU-S are the precursors of radioprotective cell subsets. All animals radioprotected for 30 days subsequently survived for at least 6 months post-transplant, and showed only host-derived hematopoiesis after 30 days. These findings suggest that rare hematopoietic stem cells survive myeloablation that can eventually repopulate irradiated hosts if myeloerythroid-restricted progenitors transiently rescue ablated animals through the critical window of bone marrow failure.
Thanyaphong Na Nakorn, David Traver, Irving L. Weissman, Koichi Akashi
TGF-βs play diverse and complex roles in many biological processes. In tumorigenesis, they can function either as tumor suppressors or as pro-oncogenic factors, depending on the stage of the disease. We have developed transgenic mice expressing a TGF-β antagonist of the soluble type II TGF-β receptor:Fc fusion protein class, under the regulation of the mammary-selective MMTV-LTR promoter/enhancer. Biologically significant levels of antagonist were detectable in the serum and most tissues of this mouse line. The mice were resistant to the development of metastases at multiple organ sites when compared with wild-type controls, both in a tail vein metastasis assay using isogenic melanoma cells and in crosses with the MMTV-neu transgenic mouse model of metastatic breast cancer. Importantly, metastasis from endogenous mammary tumors was suppressed without any enhancement of primary tumorigenesis. Furthermore, aged transgenic mice did not exhibit the severe pathology characteristic of TGF-β null mice, despite lifetime exposure to the antagonist. The data suggest that in vivo the antagonist may selectively neutralize the undesirable TGF-β associated with metastasis, while sparing the regulatory roles of TGF-βs in normal tissues. Thus this soluble TGF-β antagonist has potential for long-term clinical use in the prevention of metastasis.
Yu-an Yang, Oksana Dukhanina, Binwu Tang, Mizuko Mamura, John J. Letterio, Jennifer MacGregor, Sejal C. Patel, Shahram Khozin, Zi-yao Liu, Jeffrey Green, Miriam R. Anver, Glenn Merlino, Lalage M. Wakefield
In gastrointestinal epithelium, metaplastic conversion between predominant cell types is associated with an increased risk of neoplasia. However, the mechanisms regulating metaplastic transitions in adult epithelia are largely undefined. Here we show that matrix metalloproteinase-7 (MMP-7) is expressed not only in the majority of human pancreatic ductal adenocarcinoma specimens, but also in human pancreatic intraepithelial neoplasia and metaplastic duct lesions in human and mouse. In a mouse model of pancreatic acinar-to-ductal metaplasia, MMP-7 progressively accumulates during the metaplastic transition, resulting in a concomitant increase in solubilization of Fas ligand (FasL). Under identical conditions, mice either deficient in MMP-7 or carrying an inactive FasL gene are severely inhibited in development of progressive metaplasia and acinar cell apoptosis. Thus, MMP-7 and FasL influence the initiation and maintenance of metaplastic events in pancreatic epithelium, explaining the observed link between metaplasia and apoptosis in pancreas and other gastrointestinal tissues.
Howard C. Crawford, Charles R. Scoggins, M. Kay Washington, Lynn M. Matrisian, Steven D. Leach
Terminal epithelial cell differentiation is a crucial step in development. In the kidney, failure of terminal differentiation causes dysplasia, cystogenesis, and cancer. The present study provides multiple lines of evidence implicating the tumor suppressor protein p53 in terminal differentiation of the renal epithelium. In the developing kidney, p53 is highly enriched in epithelial cells expressing renal function genes (RFGs), such as receptors for vasoactive hormones, the sodium pump, and epithelial sodium and water channels. In comparison, proliferating renal progenitors express little if any p53 or RFGs. p53 binds to and transactivates the promoters of RFGs. In contrast, expression of a dominant negative mutant form of p53 inhibits endogenous RFG expression. Moreover, binding of endogenous p53 to the promoters of RFGs coincides with the differentiation process and is attenuated once renal epithelial cells are fully differentiated. Finally, p53-null pups exhibit a previously unrecognized aberrant renal phenotype and spatial disorganization of RFGs. Interestingly, the p53-related protein p73 is unable to functionally compensate for the loss of p53 and fails to efficiently activate RFG transcription. We conclude that p53 promotes the biochemical and morphological differentiation of the renal epithelium. Aberrations in p53-mediated terminal differentiation may therefore play a role in the pathogenesis of nephron dysgenesis and dysfunction.
Zubaida Saifudeen, Susana Dipp, Samir S. El-Dahr
Myb34.5 is a herpes simplex virus 1 (HSV-1) mutant deleted in the gene for ribonucleotide reductase (ICP6). It also carries a version of γ134.5 (a viral gene product that promotes the dephosphorylation of eIF-2α) that is under control of the E2F-responsive cellular B-myb promoter, rather than of its endogenous promoter. Myb34.5 replication in tumor cells results in their destruction (oncolysis). γ134.5 expression by HSV-1 subverts an important cell defense mechanism against viral replication by preventing shutoff of protein synthesis after viral infection. Infection of colon carcinoma cells with Myb34.5 results in greater eIF-2α dephosphorylation and viral replication compared with infection with HSV-1 mutants completely defective in γ134.5 expression. In contrast, infection of normal hepatocytes with Myb34.5 results in low levels of eIF-2α dephosphorylation and viral replication that are similar to those observed with HSV-1 mutants completely defective in γ134.5 and ICP6. When administered intravascularly into mice with diffuse liver metastases, Myb34.5 has greater antineoplastic activity than HSV-1 mutants with completely defective γ134.5 expression and more restricted biodistribution compared with HSV-1 mutants with wild-type γ134.5 expression. Myb34.5 displays reduced virulence and toxicity compared to HSV-1 mutants with wild-type γ134.5 expression. Portal venous administration of Myb34.5 significantly reduces liver tumor burden in and prolongs the life of mice with diffuse liver metastases. Preexisting Ab’s to HSV-1 do not reduce the antitumor efficacy of Myb34.5 in vivo.
Hideo Nakamura, Hideki Kasuya, John T. Mullen, Sam S. Yoon, Timothy M. Pawlik, Soundararajalu Chandrasekhar, James M. Donahue, E. Antonio Chiocca, Richard Y. Chung, Kenneth K. Tanabe
Tumors have been thought to initiate as avascular aggregates of malignant cells that only later induce vascularization. Recently, this classic concept of tumor angiogenesis has been challenged by the suggestion that tumor cells grow by co-opting preexisting host vessels and thus initiate as well-vascularized tumors without triggering angiogenesis. To discriminate between these two mechanisms, we have used intravital epifluorescence microscopy and multi-photon laser scanning confocal microscopy to visualize C6 microglioma vascularization and tumor cell behavior. To address the mechanisms underlying tumor initiation, we assessed the expression of VEGF, VEGF receptor-2 (VEGFR-2), and angiopoietin-2 (Ang-2), as well as endothelial cell proliferation. We show that multicellular aggregates (<< 1 mm3) initiate vascular growth by angiogenic sprouting via the simultaneous expression of VEGFR-2 and Ang-2 by host and tumor endothelium. Host blood vessels are not co-opted by tumor cells but rather are used as trails for tumor cell invasion of the host tissue. Our data further suggest that the established microvasculature of growing tumors is characterized by a continuous vascular remodeling, putatively mediated by the expression of VEGF and Ang-2. The results of this study suggest a new concept of vascular tumor initiation that may have important implications for the clinical application of antiangiogenic strategies.
Peter Vajkoczy, Mohammad Farhadi, Andreas Gaumann, Regina Heidenreich, Ralf Erber, Andreas Wunder, Jörg C. Tonn, Michael D. Menger, Georg Breier
We studied the role of protein kinase C isoform PKCδ in ceramide (Cer) formation, as well as in the mitochondrial apoptosis pathway induced by anticancer drugs in prostate cancer (PC) cells. Etoposide and paclitaxel induced Cer formation and apoptosis in PKCδ-positive LNCaP and DU145 cells but not in PKCδ-negative LN-TPA or PC-3 cells. In contrast, these drugs induced mitotic cell cycle arrest in all PC cell lines. Treatment with Rottlerin, a specific PKCδ inhibitor, significantly inhibited drug-induced Cer formation and apoptosis in LNCaP cells, as did overexpression of dominant negative–type PKCδ. Overexpression of wild-type PKCδ had an opposite effect in PC-3 cells. Notably, etoposide induced biphasic Cer formation in LNCaP cells. The early and transient Cer increase resulted from de novo Cer synthesis, while the late and sustained Cer accumulation was derived from sphingomyelin hydrolysis by neutral sphingomyelinase (nSMase). Cer, in turn, induced mitochondrial translocation of PKCδ and stimulated the activity of this kinase, promoting cytochrome c release and caspase-9 activation. Furthermore, the specific caspase-9 inhibitor LEHD-fmk significantly inhibited etoposide-induced nSMase activation, Cer accumulation, and PKCδ mitochondrial translocation. These results indicate that PKCδ plays a crucial role in activating anticancer drug–induced apoptosis signaling by amplifying the Cer-mediated mitochondrial amplification loop.
Makoto Sumitomo, Motoi Ohba, Junichi Asakuma, Takako Asano, Toshio Kuroki, Tomohiko Asano, Masamichi Hayakawa
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