The cancer stem cell hypothesis suggests that malignant growth depends on a subset of tumor cells with stem cell-like properties of self-renewal. Because hedgehog (Hh) signaling regulates progenitor cell fate in normal development and homeostasis, aberrant pathway activation might be involved in the maintenance of such a population in cancer. Indeed, mutational activation of the Hh pathway is associated with medulloblastoma and basal cell carcinoma; pathway activity is also critical for growth of other tumors lacking such mutations, although the mechanism of pathway activation is poorly understood. Here we study the role and mechanism of Hh pathway activation in multiple myeloma (MM), a malignancy with a well defined stem cell compartment. In this model, rare malignant progenitors capable of clonal expansion resemble B cells, whereas the much larger tumor cell population manifests a differentiated plasma cell phenotype that pathologically defines the disease. We show that the subset of MM cells that manifests Hh pathway activity is markedly concentrated within the tumor stem cell compartment. The Hh ligand promotes expansion of MM stem cells without differentiation, whereas the Hh pathway blockade, while having little or no effect on malignant plasma cell growth, markedly inhibits clonal expansion accompanied by terminal differentiation of purified MM stem cells. These data reveal that Hh pathway activation is heterogeneous across the spectrum of MM tumor stem cells and their more differentiated progeny. The potential existence of similar relationships in other adult cancers may have important biologic and clinical implications for the study of aberrant Hh signaling.cancer stem cells ͉ cancer therapy ͉ cyclopamine

Background & Aims-The molecular mechanism underlying epithelial metaplasia in Barrett's esophagus remains unknown. Recognizing that Hedgehog signaling is required for early esophageal development, we sought to determine if the Hedgehog pathway is reactivated in Barrett's esophagus, and if genes downstream of the pathway could promote columnar differentiation of esophageal epithelium.

Medulloblastoma is an embryonal tumor thought to arise from the granule cell precursors (GCPs) of the cerebellum. PATCHED (PTCH), an inhibitor of Hedgehog signaling, is the best-characterized tumor suppressor in medulloblastoma. However, <20% of medulloblastomas have mutations in PTCH. In the search for other tumor suppressors, interest has focused on the deletion events at the 17p13.3 locus, the most common genetic defect in medulloblastoma. This chromosomal region contains HYPERMETHYLATED IN CANCER 1 (HIC1), a transcriptional repressor that is a frequent target of epigenetic gene silencing in medulloblastoma. Here we use a mouse model of Ptch1 heterozygosity to reveal a critical tumor suppressor function for Hic1 in medulloblastoma. When compared with Ptch1 heterozygous mutants, compound Ptch1/Hic1 heterozygotes display a fourfold increased incidence of medulloblastoma. We show that Hic1 is a direct transcriptional repressor of Atonal Homolog 1 (Atoh1), a proneural transcription factor essential for cerebellar development, and show that ATOH1 expression is required for human medulloblastoma cell growth in vitro. Given that Atoh1 is also a putative target of Hh signaling, we conclude that the Hic1 and Ptch1 tumor suppressors cooperate to silence Atoh1 expression during a critical phase in GCP differentiation in which malignant transformation may lead to medulloblastoma.[Keywords: HIC1; PTCH; ATOH1; Math1; medulloblastoma] Supplemental material is available at http://www.genesdev.org.

Transplantation of human fetal neural stem cells (hNSCs) previously demonstrated significant functional recovery after spinal cord contusion in rats. Other studies indicated that human mesenchymal stem cells (hMSCs) can home to areas of damage and cross the blood–brain barrier. The purpose of this article is to determine if combined administration of mesenchymal stem cells and neuronal stem cells improves functional outcomes in rats. The study design was a randomized controlled animal trial. Female adult Long-Evans hooded rats underwent laminectomy at T10 level. Moderate spinal cord contusion at T10 level was induced by the MASCIS Impactor. Four groups were identified. The MSC + NSC group received hMSCs intravenously (IV) immediately after spinal cord injury (acute) and returned 1 week later (subacute) for injection of hNSC directly at site of injury. The MSC-only group received hMSC IV acutely and cell media subacutely. The NSC-only group received cell media IV acutely and hNSC subacutely. The control group received cell media IV acutely and subacutely. Subjects were assessed for 6 weeks using Basso, Beattie, Bresnahan Locomotor Rating Score. Twenty-four subjects were utilized, six subjects in each group. Statistically significant functional improvement was seen in the MSC + NSC group and the NSC-only group versus controls (p = 0.027, 0.042, respectively). The MSC-only group did not demonstrate a significant improvement over control (p = 0.145). Comparing the MSC + NSC group and the NSC-only group, there was no significant difference (p = 0.357). Subacute transplantation of hNSCs into contused spinal cord of rats led to significant functional recovery when injected either with or without acute IV administration of hMSCs. Neither hMSCs nor addition of hMSC to hNSC resulted in significant improvement.