BACKGROUND & AIMS Reserve intestinal stem cells (rISCs) are quiescent/slowly cycling under homeostatic conditions, allowing for their identification with label-retention assays. rISCs mediate epithelial regeneration after tissue damage by converting to actively proliferating stem cells (aISCs) that self renew and demonstrate multipotency, which are defining properties of stem cells. Little is known about the genetic mechanisms that regulate the production and maintenance of rISCs. High expression levels of the transcription factor Sox9 (Sox9high) are associated with rISCs. This study investigates the role of SOX9 in regulating the rISC state. METHODS We used fluorescence-activated cell sorting to isolate cells defined as aISCs (Lgr5high) and rISCs (Sox9high) from Lgr5EGFP and Sox9EGFP reporter mice. Expression of additional markers associated with active and reserve ISCs were assessed in Lgr5high and Sox9high populations by single-cell gene expression analyses. We used label-retention assays to identify whether Sox9high cells were label-retatining cells (LRCs). Lineage-tracing experiments were performed in Sox9-CreERT2 mice to measure the stem cell capacities and radioresistance of Sox9-expressing cells. Conditional SOX9 knockout mice and inducible-conditional SOX9 knockout mice were used to determine whether SOX9 was required to maintain LRCs and rISC function. RESULTS Lgr5high and a subset of crypt-based Sox9high cells co-express markers of aISC and rISC (Lgr5. Bmi1. Lrig1, and Hopx). LRCs express high levels of Sox9 and are lost in SOX9-knockout mice. SOX9 is required for epithelial regeneration after high-dose irradiation. Crypts from SOX9-knockout mice have increased sensitivity to radiation, compared with control mice, which could not be attributed to impaired cell-cycle arrest or DNA repair. CONCLUSIONS SOX9 limits proliferation in LRCs and imparts radiation resistance to rISCs in mice.

Lysophosphatidic acid (LPA) is a bioactive lipid that promotes cancer cell proliferation and motility through activation of cell surface G protein -coupled receptors. Here, we provide the first evidence that LPA reduces the cellular abundance of the tumor suppressor p53 in A549 lung carcinoma cells, which express endogenous LPA receptors. The LPA effect depends on increased proteasomal degradation of p53 and it results in a corresponding decrease in p53-mediated transcription. Inhibition of phosphatidylinositol 3-kinase protected cells from the LPA-induced reduction of p53, which implicates this signaling pathway in the mechanism of LPA-induced loss of p53. LPA partially protected A549 cells from actinomycin D induction of both apoptosis and increased p53 abundance. Expression of LPA 1 , LPA 2 , and LPA 3 receptors in HepG2 hepatoma cells, which normally do not respond to LPA, also decreased p53 expression and p53-dependent transcription. In contrast, neither inactive LPA 1 (R124A) nor another G i -coupled receptor, the M 2 muscarinic acetylcholine receptor, reduced p53-dependent transcription in HepG2 cells. These results identify p53 as a target of LPA action and provide a new dimension for understanding how LPA stimulates cancer cell division, protects against apoptosis, and thereby promotes tumor progression.

Epigenetic in vitro and in vivo studies suggest that suppressor of cytokine signaling-2 (SOCS2) may normally limit tumorigenesis in the intestine; however, this theory has not been directly tested. We hypothesized that SOCS2 deficiency promotes spontaneous intestinal tumorigenesis in Apc(Min/+) mice. Therefore, we quantified tumor number, size, and load in the small intestine and colon using SOCS2(+/+)/Apc(Min/+), SOCS2(+/-)/Apc(Min/+), and SOCS2(-/-)/Apc(Min/+) mice and assayed hematocrit as an indirect marker of disease severity. Biochemical and histological assays were used to assess mechanisms. Heterozygous and homozygous disruption of SOCS2 alleles promoted 166 and 441% increases in tumor load in the small intestine, respectively, accelerated development of colon tumors, and caused severe anemia. SOCS2 deletion promoted significant increases in intestinal insulin-like growth factor-I mRNA but did not affect plasma insulin-like growth factor-I. Western blots and immunohistochemical analysis demonstrated that tumor and nontumor intestinal tissue of SOCS2(-/-)/Apc(Min/+) mice had increased serine 727 phosphorylation of signal transducer and activator of transcription 3 compared with SOCS2(+/+)/Apc(Min/+) mice. Moreover, electromobility shift assays showed that SOCS2 deletion did not alter signal transducer and activator of transcription 3 DNA binding. However, tumors and small intestine from SOCS2(-/-)/Apc(Min/+) showed dramatic increases in activator protein-1 (AP-1) DNA binding, and SOCS2 overexpression in vitro reduced levels of AP-1. These studies indicate that SOCS2 deletion promotes the spontaneous development of intestinal tumors driven by mutations in the adenomatous polyposis coli/beta-catenin pathway and activates AP-1. Therefore, reduced expression or epigenetic silencing of SOCS2 may serve as a useful biomarker for colorectal cancer risk.

No abstract

Insulin‐like growth factor I (IGF‐I) and epidermal growth factor (EGF) increase risk and promote pathogenesis of colon cancer in humans. Studies suggest that these pathways may interact to promote synergistic effects on colon cancer cells. We tested the hypothesis that combined IGF‐I and EGF treatment will additively or synergistically increase proliferation of intestinal epithelial cells and activate tumor‐promoting pathways, such as the β‐catenin pathway. IEC‐6 cells, a non‐transformed intestinal epithelial cell line, were treated with IGF‐I and EGF, alone or in combination. DNA synthesis was assayed using H3‐thymidine. EGF stimulated DNA synthesis more potently than IGF‐I, but combined IGF and EGF treatment synergistically increased DNA synthesis. EGF pretreatment, followed by IGF‐I treatment increased IGF‐IR tyrosine phosphorylation. EGF alone increased total IGF‐IR and this was enhanced by EGF pretreatment and subsequent IGF‐I treatment. EGF increased nuclear β‐catenin and synergistically enhanced IGF‐I‐induced nuclear β‐catenin. Ongoing studies will determine whether inhibition of both IGF‐IR and EGFR signaling decreases tumorigenesis, in vivo. These studies suggest that interactions between IGF‐I and EGF may reduce the effectiveness of anti‐cancer therapies that specifically target these pathways in colon cancer. [NIH‐DK40274‐16 RO1 and NIH‐DK44769‐10 CCFA].

No abstract

No abstract