Subpopulations of cancer stem-like cells (CSC) are thought to drive tumor progression and posttreatment recurrence in multiple solid tumors. However, the mechanisms that maintain stable proportions of self-renewing CSC within heterogeneous tumors under homeostatic conditions remain poorly understood. Progastrin is a secreted peptide that exhibits tumorforming potential in colorectal cancer, where it regulates pathways known to modulate colon CSC behaviors. In this study, we investigated the role of progastrin in regulating CSC phenotype in advanced colorectal cancer. Progastrin expression and secretion were highly enriched in colon CSC isolated from human colorectal cancer cell lines and colon tumor biopsies.Progastrin expression promoted CSC self-renewal and survival, whereas its depletion by RNA interference-mediated or antibody-mediated strategies altered the homeostatic proportions of CSC cells within heterogeneous colorectal cancer tumors. Progastrin downregulation also decreased the frequency of ALDH high cells, impairing their tumor-initiating potential, and inhibited the high glycolytic activity of ALDH high CSC to limit their self-renewal capability. Taken together, our results show how colorectal CSC maintain their tumor-initiating and selfrenewal capabilities by secreting progastrin, thereby contributing to the tumor microenvironment to support malignancy.

No abstract

Myelodysplastic syndrome (MDS) is characterized by ineffective hematopoiesis with resultant cytopenias. Increased apoptosis and aberrantly functioning progenitors are thought to contribute to this phenotype. As is the case for other malignancies, overcoming apoptosis is believed to be important in progression toward acute myeloid leukemia (AML). Using the NUP98-HOXD13 (NHD13) transgenic mouse model of MDS, we previously reported that overexpression of the anti-apoptotic protein BCL2, blocked apoptosis and improved cytopenias, paradoxically, delaying leukemic progression. To further understand this surprising result, we examined the role of p53 and its pro-apoptotic effectors, PUMA and NOXA in NHD13 mice. The absence of p53 or PUMA but not NOXA reduced apoptosis and expanded the numbers of MDS-repopulating cells. Despite a similar effect on apoptosis and cell numbers, the absence of p53 and PUMA had diametrically opposed effects on progression to AML: absence of p53 accelerated leukemic progression, while absence of PUMA significantly delayed progression. This may be explained in part by differences in cellular responses to DNA damage. The absence of p53 led to higher levels of γ-H2AX (indicative of persistent DNA lesions) while PUMA-deficient NHD13 progenitors resolved DNA lesions in a manner comparable to wild-type cells. These results suggest that targeting PUMA may improve the cytopenias of MDS without a detrimental effect on leukemic progression thus warranting further investigation. Cell Death and Differentiation (2016) 23, 1049-1059 doi:10.1038/cdd.2015; published online 8 January 2016Myelodysplastic syndromes (MDS) are a genetically and clonally heterogeneous group of myeloid malignancies, likely arising from the hematopoietic stem cell. 1-3 Despite their genetic heterogeneity, they share common phenotypic features including low peripheral blood counts (cytopenias) in spite of a hypercellular bone marrow (ineffective hematopoiesis), dysplasia and a variable propensity for transformation to acute myeloid leukemia (AML). 4 Programmed cell death or apoptosis of white blood cells is a common feature, and is thought to contribute to the cytopenias particularly in early stages of the disease. The basis of ineffective hematopoiesis in MDS may also lie in the dysfunction of hematopoietic progenitors and their inability to support adequate bone marrow function. Apoptosis can be triggered by extrinsic factors, such as FAS ligand or TNF-α, or by cell-intrinsic factors such as ribosomal stress or increased reactive oxygen species. A cell extrinsic mechanism for apoptosis in MDS has been favored for many years; 5 however, recent evidence suggests a cell-intrinsic trigger, especially in del(5q) MDS for which there is evidence for activation of the tumor suppressor p53 by ribosomal dysfunction. 6,7 More aggressive stages of MDS have less apoptosis than earlier stages, 8 supporting the paradigm that acquired resistance to apoptosis of malignant progenitors is an important step in cancer progression. 9 Among hematological...

<div>Abstract<p>Subpopulations of cancer stem–like cells (CSC) are thought to drive tumor progression and posttreatment recurrence in multiple solid tumors. However, the mechanisms that maintain stable proportions of self-renewing CSC within heterogeneous tumors under homeostatic conditions remain poorly understood. Progastrin is a secreted peptide that exhibits tumor-forming potential in colorectal cancer, where it regulates pathways known to modulate colon CSC behaviors. In this study, we investigated the role of progastrin in regulating CSC phenotype in advanced colorectal cancer. Progastrin expression and secretion were highly enriched in colon CSC isolated from human colorectal cancer cell lines and colon tumor biopsies. Progastrin expression promoted CSC self-renewal and survival, whereas its depletion by RNA interference–mediated or antibody-mediated strategies altered the homeostatic proportions of CSC cells within heterogeneous colorectal cancer tumors. Progastrin downregulation also decreased the frequency of ALDH^high cells, impairing their tumor-initiating potential, and inhibited the high glycolytic activity of ALDH^high CSC to limit their self-renewal capability. Taken together, our results show how colorectal CSC maintain their tumor-initiating and self-renewal capabilities by secreting progastrin, thereby contributing to the tumor microenvironment to support malignancy. <i>Cancer Res; 76(12); 3618–28. ©2016 AACR</i>.</p></div>

<div>Abstract<p>Subpopulations of cancer stem–like cells (CSC) are thought to drive tumor progression and posttreatment recurrence in multiple solid tumors. However, the mechanisms that maintain stable proportions of self-renewing CSC within heterogeneous tumors under homeostatic conditions remain poorly understood. Progastrin is a secreted peptide that exhibits tumor-forming potential in colorectal cancer, where it regulates pathways known to modulate colon CSC behaviors. In this study, we investigated the role of progastrin in regulating CSC phenotype in advanced colorectal cancer. Progastrin expression and secretion were highly enriched in colon CSC isolated from human colorectal cancer cell lines and colon tumor biopsies. Progastrin expression promoted CSC self-renewal and survival, whereas its depletion by RNA interference–mediated or antibody-mediated strategies altered the homeostatic proportions of CSC cells within heterogeneous colorectal cancer tumors. Progastrin downregulation also decreased the frequency of ALDH^high cells, impairing their tumor-initiating potential, and inhibited the high glycolytic activity of ALDH^high CSC to limit their self-renewal capability. Taken together, our results show how colorectal CSC maintain their tumor-initiating and self-renewal capabilities by secreting progastrin, thereby contributing to the tumor microenvironment to support malignancy. <i>Cancer Res; 76(12); 3618–28. ©2016 AACR</i>.</p></div>

<p>Legend for Supplemental Figures S1-S6.</p>

<p>Description of additional methods and procedures used in the study.</p>

<p>shRNA-mediated down regulation of progastrin in vitro and in vivo.</p>