title: Somatostatin signaling via SSTR1 contributes to the quiescence of colon cancer stem cells.
abstract: Neuroendocrine cells (NECs) reside adjacent to colonic stem cells (SCs) in the crypt stem cell (SC) niche, but how NECs are involved in regulation of SCs is unclear. We investigated NECs expressing somatostatin (SST) and somatostatin receptor type 1 (SSTR1) because SST inhibits intestinal proliferation.
  
  
  
  SSTR1 cells maintain SCs in a quiescent state, and aberrant SST signaling contributes to SC overpopulation in colorectal cancer (CRC).
  
  
  
  The proportion of SCs to NECs cells was quantified, by flow cytometry, in CRC cell lines and primary normal/tumor tissues based on cellular ALDH and SSTR1 levels, respectively. Doubling time and sphere-formation was used to evaluate cell proliferation and stemness. CRC cell lines were treated with exogenous SST and SST inhibitor cyclosomatostatin (cycloSST) and analyzed for changes in SCs and growth rate. Paracrine signaling between NECs and SCs was ascertained using transwell cultures of ALDH+ and SSTR1+ cells.
  
  
  
  In CRC cell lines, the proportion of ALDH+ cells inversely correlates with proportion of SSTR1+ cells and with rate of proliferation and sphere-formation. While primary normal tissue shows SST and SSTR1 expression, CRC shows only SSTR1 expression. Moreover, ALDH+ cells did not show SST or SSTR1 expression. Exogenous SST suppressed proliferation but not ALDH+ population size or viability. Inhibition of SSTR1 signaling, via cycloSST treatment, decreased cell proliferation, ALDH+ cell population size and sphere-formation. When co-cultured with SSTR1+ cells, sphere-formation and cell proliferation of ALDH+ cells was inhibited.
  
  
  
  That each CRC cell line has a unique ALDH+/SSTR1+ ratio which correlates with its growth dynamics, suggests feedback mechanisms exist between SCs and NECs that contribute to regulation of SCs. The growth suppression by both SST and cycloSST treatments suggests that SST signaling modulates this feedback mechanism. The ability of SSTR1+ cells to decrease sphere formation and proliferation of ALDH+ cells in transwell cultures indicates that the ALDH subpopulation is regulated by SSTR1 via a paracrine mechanism. Since ALDH+ cells lack SST and SSTR1 expression, we conjecture that SST signaling controls the rate of NEC maturation as SCs mature along the NEC lineage, which contributes to quiescence of SCs and inhibition of proliferation.
authors.affiliation: Department of Biological Sciences, University of Delaware, 118 Wolf Hall, Newark, DE, 19716, USA.|Center for Translational Cancer Research, Helen F. Graham Cancer Center and Research Institute, 4701 Ogletown-Stanton Rd, Newark, DE, 19713, USA.
authors.forename: Shirin R
authors.initials: SR
authors.lastname: Modarai
authors.affiliation: Department of Biological Sciences, University of Delaware, 118 Wolf Hall, Newark, DE, 19716, USA.|Center for Translational Cancer Research, Helen F. Graham Cancer Center and Research Institute, 4701 Ogletown-Stanton Rd, Newark, DE, 19713, USA.
authors.forename: Lynn M
authors.initials: LM
authors.lastname: Opdenaker
authors.affiliation: Department of Biological Sciences, University of Delaware, 118 Wolf Hall, Newark, DE, 19716, USA.
authors.forename: Vignesh
authors.initials: V
authors.lastname: Viswanathan
authors.affiliation: CATX Inc., Gladwyne, PA, 19035, USA.
authors.forename: Jeremy Z
authors.initials: JZ
authors.lastname: Fields
authors.affiliation: Department of Biological Sciences, University of Delaware, 118 Wolf Hall, Newark, DE, 19716, USA. brucemboman@gmail.com.|Center for Translational Cancer Research, Helen F. Graham Cancer Center and Research Institute, 4701 Ogletown-Stanton Rd, Newark, DE, 19713, USA. brucemboman@gmail.com.
authors.forename: Bruce M
authors.initials: BM
authors.lastname: Boman
mesh_terms: D000444:Aldehyde Dehydrogenase / Q000235:genetics / Q000378:metabolism; D045744:Cell Line, Tumor; D049109:Cell Proliferation; D003106:Colon / Q000378:metabolism; D003110:Colonic Neoplasms / Q000235:genetics / Q000378:metabolism* / Q000473:pathology; D015972:Gene Expression Regulation, Neoplastic; D006801:Humans; D007413:Intestinal Mucosa / Q000378:metabolism / Q000473:pathology; D014411:Neoplastic Stem Cells / Q000187:drug effects / Q000378:metabolism*; D017481:Receptors, Somatostatin / Q000378:metabolism*; D016192:Resting Phase, Cell Cycle; D015398:Signal Transduction; D013004:Somatostatin / Q000378:metabolism* / Q000494:pharmacology
chemical_list: D017481:Receptors, Somatostatin; C101130:somatostatin receptor type 1; D013004:Somatostatin; D000444:Aldehyde Dehydrogenase