Wnt signaling suppresses MAPK-driven proliferation of intestinal stem cells
Zahra Kabiri, … , Christopher M. Counter, David M. Virshup
Zahra Kabiri, … , Christopher M. Counter, David M. Virshup
Published July 30, 2018
Citation Information: J Clin Invest. 2018;128(9):3806-3812. https://doi.org/10.1172/JCI99325.
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Concise Communication Gastroenterology

Wnt signaling suppresses MAPK-driven proliferation of intestinal stem cells

Abstract

Intestinal homeostasis depends on a slowly proliferating stem cell compartment in crypt cells, followed by rapid proliferation of committed progenitor cells in the transit amplifying (TA) compartment. The balance between proliferation and differentiation in intestinal stem cells (ISCs) is regulated by Wnt/β-catenin signaling, although the mechanism remains unclear. We previously targeted PORCN, an enzyme essential for all Wnt secretion, and demonstrated that stromal production of Wnts was required for intestinal homeostasis. Here, a PORCN inhibitor was used to acutely suppress Wnt signaling. Unexpectedly, the treatment induced an initial burst of proliferation in the stem cell compartment of the small intestine, due to conversion of ISCs into TA cells with a loss of intrinsic ISC self-renewal. This process involved MAPK pathway activation, as the proliferating cells in the base of the intestinal crypt contained phosphorylated ERK1/2, and a MEK inhibitor attenuated the proliferation of ISCs and their differentiation into TA cells. These findings suggest a role for Wnt signaling in suppressing the MAPK pathway at the crypt base to maintain a pool of ISCs. The interaction between Wnt and MAPK pathways in vivo has potential therapeutic applications in cancer and regenerative medicine.

Authors

Zahra Kabiri, Gediminas Greicius, Hamed Zaribafzadeh, Amanda Hemmerich, Christopher M. Counter, David M. Virshup

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Figure 4

Suppressing MAPK signaling inhibits C59-induced proliferation of intestinal stem cells.

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Suppressing MAPK signaling inhibits C59-induced proliferation of intesti...
(A) Schematic time line of trametinib, C59, and vehicle (Veh) administration in mice. Trametinib was administered (3 mg/kg, QD) 32 hours prior to administration of vehicle or C59 (100 mg/kg, QD). A total of 4 doses of trametinib and 2 doses of C59 or vehicle were gavaged according to hourly time point (indicated by arrows) prior to euthanasia. (B) The combination of trametinib and C59 treatment blocked proliferation and impaired intestinal homeostasis. EdU was injected 2 hours prior to euthanasia into 4 groups of mice treated with either vehicle or C59 alone, or in combination with trametinib (Tram). Left panels show representative images of total EdU+ staining in jejunal crypts. Right panels show higher magnification of crypt as indicated. Scale bar, 25 μm. (C) Top graph shows the number of counts for EdU+ cells within 10 cells in the base of the crypt. NS, nonsignificant; *P < 0.05; ***P < 0.001, Kruskal-Wallis 1-way ANOVA test. (D) Trametinib blocks PORCN inhibition–induced burst of proliferation. The number of EdU+ cells per 10 cells of the crypt base was determined. C59 treatment increased the number of crypts with 4 or more EdU+ cells, and this was reversed by coadministration of trametinib. Vehicle, n = 7. Trametinib plus vehicle, n = 6. C59, n = 8. Trametinib plus C59, n = 6. Error bar indicates SEM; 2 experimental replicates.