Dietary Pectin Increases Intestinal Crypt Stem Cell Survival following Radiation Injury.

Gastrointestinal (GI) mucosal damage is a devastating adverse effect of radiation therapy. We have recently reported that expression of Dclk1, a Tuft cell and tumor stem cell (TSC) marker, 24h after high dose total-body gamma-IR (TBI) can be used as a surrogate marker for crypt survival. Dietary pectin has been demonstrated to possess chemopreventive properties, whereas its radioprotective property has not been studied. The aim of this study was to determine the effects of dietary pectin on ionizing radiation (IR)-induced intestinal stem cell (ISC) deletion, crypt and overall survival following lethal TBI. C57BL/6 mice received a 6% pectin diet and 0.5% pectin drinking water (pre-IR mice received pectin one week before TBI until death; post-IR mice received pectin after TBI until death). Animals were exposed to TBI (14 Gy) and euthanized at 24 and 84h post-IR to assess ISC deletion and crypt survival respectively. Animals were also subjected to overall survival studies following TBI. In pre-IR treatment group, we observed a three-fold increase in ISC/crypt survival, a two-fold increase in Dclk1+ stem cells, increased overall survival (median 10d vs. 7d), and increased expression of Dclk1, Msi1, Lgr5, Bmi1, and Notch1 (in small intestine) post-TBI in pectin treated mice compared to controls. We also observed increased survival of mice treated with pectin (post-IR) compared to controls. Dietary pectin is a radioprotective agent; prevents IR-induced deletion of potential reserve ISCs; facilitates crypt regeneration; and ultimately promotes overall survival. Given the anti-cancer activity of pectin, our data support a potential role for dietary pectin as an agent that can be administered to patients receiving radiation therapy to protect against radiation-induces mucositis.

cDNA cloning, DNA binding, and evolution of mammalian transcription factor IIIA.

cDNA for rat transcription factor IIIA (TFIIIA) was cloned by degenerate PCR and rapid amplification of cDNA ends. This cDNA coded for a protein with nine Cys(2)His(2) zinc fingers and a non-finger C-terminal tail; 63% amino acid (aa) sequence identity was observed with the Xenopus TFIIIA zinc finger region. Recombinant rat protein containing only the nine fingers afforded DNase I protection of the identical nucleotides protected by Xenopus laevis native TFIIIA on the Xenopus 5S RNA gene internal control region. A putative mouse TFIIIA clone was identified in an expressed sequence tag database by sequence similarity to rat TFIIIA. Recombinant nine-finger protein from this clone afforded DNase I protection of the Xenopus 5S rRNA gene like the native frog protein as did a recombinant nine-finger form of a putative human TFIIIA clone. These DNA binding results demonstrate that these clones code for the respective mammalian TFIIIAs. Rodent and human TFIIIAs share about 87% aa sequence identity in their zinc finger regions and have evolved to about the same extent as X. laevis and Xenopus borealis TFIIIAs. A monoclonal antibody against human p53 tumor suppressor bound to rat and mouse TFIIIA but not to human TFIIIA in Western blots. The N-terminal regions of rodent and human TFIIIA do not contain the oocyte-specific initiating Met and accompanying conserved residues found in fish and amphibian TFIIIAs. In their non-finger C-terminal tails, mammalian and amphibian TFIIIAs share a conserved transcription activation domain as well as conserved nuclear localization and nuclear export signals.