Intestinal Epithelial HuR Modulates Distinct Pathways of Proliferation and Apoptosis and Attenuates Small Intestinal and Colonic Tumor Development

Abstract

HuR is a ubiquitous nucleocytoplasmic RNA binding protein that exerts pleiotropic effects on cell growth and tumorigenesis. In this study, we explored the impact of conditional, tissue-specific genetic deletion of HuR on intestinal growth and tumorigenesis in mice. Mice lacking intestinal expression of HuR (Hur IKO mice) displayed reduced levels of cell proliferation in the small intestine and increased sensitivity to doxorubicin-induced acute intestinal injury, as evidenced by decreased villus height and a compensatory shift in proliferating cells. In the context of ApcMin mice, a transgenic model of intestinal tumorigenesis, intestinal deletion of the HuR gene caused a 3-fold decrease in tumor burden characterized by reduced proliferation, increased apoptosis and decreased expression of transcripts encoding anti-apoptotic HuR target RNAs. Similarly, Hur IKO mice subjected to an inflammatory colon carcinogenesis protocol (AOM-DSS administration) exhibited a 2-fold decrease in tumor burden. Hur IKO mice showed no change in ileal Asbt expression, fecal bile acid excretion or enterohepatic pool size that might explain the phenotype. Moreover, none of the HuR targets identified in Apc Min/+Hur IKO were altered in AOM-DSS treated Hur IKO mice, the latter of which exhibited increased apoptosis of colonic epithelial cells where elevation of a unique set of HuR-targeted pro-apoptotic factors was documented. Taken together, our results promote the concept of epithelial HuR as a contextual modifier of pro-apoptotic gene expression in intestinal cancers, acting independently of bile acid metabolism to promote cancer. In the small intestine, epithelial HuR promotes expression of pro-survival transcripts that support Wnt-dependent tumorigenesis, whereas in the large intestine epithelial HuR indirectly downregulates certain pro-apoptotic RNAs to attenuate colitis-associated cancer.

Delivery of Therapeutics Targeting the mRNA-Binding Protein HuR Using 3DNA Nanocarriers Suppresses Ovarian Tumor Growth

“…Our previous studies in preclinical pancreatic cancer models (33)(34)(35)(36)(37)(38), as well as studies by others (17,19,20,24,(39)(40)(41), provided the rationale for investigating HuR inhibition in ovarian tumors We first established that suppression of HuR expression reduces proliferation, anchorage-independent growth, and invasion of ovarian cancer cells in vitro. We further demonstrate HuR inhibitionmediated reduction in tumor growth rate, delay in ascites development, and extension of lifespan by nearly 1.5-fold in two different ovarian cancer mouse models, a xenograft model and an orthotopic model in which mice bear tumors throughout the peritoneum.…”

“…The role of HuR in posttranscriptional regulation of multiple genes that promote survival of ovarian tumor cells provides an opportunity to develop an alternative strategy that targets multiple core signaling pathways at once. Indeed, proof-of-concept studies using HuR knockout mice and intracranial injection of mice with genetically silenced HuR primary glioblastoma cells have shown a reduction in colon tumor and glioblastoma growth, respectively (19,20). One approach to inhibit HuR is through targeted delivery of functional siRNA.…”

Characterization of Colorectal Cancer Development in Apc min/+ Mice

“…Measure fecal bile acid output from stool (collected for 72 h from individually housed mouse) [15] if desired. This step is optional.…”

“…Determine bile acid pool size from total content of small intestine, gallbladder, and liver following sacrifice (optional) if desired [15]. …”

HuR Enhances Early Restitution of the Intestinal Epithelium by Increasing Cdc42 Translation

“…HuR is crucial for the maintenance of hematopoietic stem cells (27), the selection and chemotaxis of T cells (24), and B-cell development and activation/differentiation following an antigen encounter (28). Our previous study (29) and findings from others (30) have shown that conditional deletion of HuR in intestinal epithelial cells (IECs) inhibits mucosal growth in the small intestine and reduces tumor development by targeting multiple genes including the Wnt coreceptor Lrp6. Here, we study the role of HuR in the regulation of intestinal mucosal repair after acute injury and demonstrate that HuR enhances early epithelial restitution by activating translation of the mRNA that encodes the small GTP-binding protein Cdc42.…”