Divergent Dynamics and Functions of ERK MAP Kinase Signaling in Development, Homeostasis and Cancer: Lessons from Fluorescent Bioimaging

The extracellular signal-regulated kinase (ERK) signaling pathway regulates a variety of biological processes including cell proliferation, survival, and differentiation. Since ERK activation promotes proliferation of many types of cells, its deregulated/constitutive activation is among general mechanisms for cancer. Recent advances in bioimaging techniques have enabled to visualize ERK activity in real-time at the single-cell level. Emerging evidence from such approaches suggests unexpectedly complex spatiotemporal dynamics of ERK activity in living cells and animals and their crucial roles in determining cellular responses. In this review, we discuss how ERK activity dynamics are regulated and how they affect biological processes including cell fate decisions, cell migration, embryonic development, tissue homeostasis, and tumorigenesis

HOXA5 Counteracts Stem Cell Traits by Inhibiting Wnt Signaling in Colorectal Cancer

Hierarchical organization of tissues relies on stem cells, which either self-renew or produce committed progenitors predestined for lineage differentiation. Here we identify HOXA5 as an important repressor of intestinal stem cell fate in vivo and identify a reciprocal feedback between HOXA5 and Wnt signaling. HOXA5 is suppressed by the Wnt pathway to maintain stemness and becomes active only outside the intestinal crypt where it inhibits Wnt signaling to enforce differentiation. In colon cancer, HOXA5 is downregulated, and its re-expression induces loss of the cancer stem cell phenotype, preventing tumor progression and metastasis. Tumor regression by HOXA5 induction can be triggered by retinoids, which represent tangible means to treat colon cancer by eliminating cancer stem cells

Biomaterials for intestinal organoid technology and personalized disease modelling

Recent advances in intestinal organoid technologies have paved the way for in vitro recapitulation of the homeostatic renewal of adult tissues, tissue or organ morphogenesis during development, and pathogenesis of many disorders. In vitro modelling of individual patient diseases using organoid systems have been considered key in establishing rational design of personalized treatment strategies and in improving therapeutic outcomes. In addition, the transplantation of organoids into diseased tissues represents a novel approach to treat currently incurable diseases. Emerging evidence from intensive studies suggests that organoid systems’ development and functional maturation depends on the presence of an extracellular matrix with suitable biophysical properties, where advanced synthetic hydrogels open new avenues for theoretical control of organoid phenotypes and potential applications of organoids in therapeutic purposes. In this review, we discuss the status, applications, challenges and perspectives of intestinal organoid systems emphasising on hydrogels and their properties suitable for intestinal organoid culture. We provide an overview of hydrogels used for intestinal organoid culture and key factors regulating their biological activity. The comparison of different hydrogels would be a theoretical basis for establishing design principles of synthetic niches directing intestinal cell fates and functions

Antagonistic Interactions between Extracellular Signal-Regulated Kinase Mitogen-Activated Protein Kinase and Retinoic Acid Receptor Signaling in Colorectal Cancer Cells

Deregulated activation of RAS/extracellular signal-regulated kinase (ERK) signaling and defects in retinoic acid receptor (RAR) signaling are both implicated in many types of cancers. However, interrelationships between these alterations in regulating cancer cell fates have not been fully elucidated. Here, we show that RAS/ERK and RAR signaling pathways antagonistically interact with each other to regulate colorectal cancer (CRC) cell fates. We show that RAR signaling activation promotes spontaneous differentiation of CRC cells, while ERK activation suppresses it. Our microarray analyses identify genes whose expression levels are upregulated by RAR signaling. Notably, one of these genes, MKP4, encoding a member of dual-specificity phosphatases for mitogen-activated protein (MAP) kinases, mediates ERK inactivation upon RAR activation, thereby promoting the differentiation of CRC cells. Moreover, our results also show that RA induction of RAR target genes is suppressed by the ERK pathway activation. This suppression results from the inhibition of RAR transcriptional activity, which is shown to be mediated through an RIP140/histone deacetylase (HDAC)-mediated mechanism. These results identify antagonistic interactions between RAS/ERK and RAR signaling in the cell fate decision of CRC cells and define their underlying molecular mechanisms

ERK MAP Kinase Signaling Regulates RAR Signaling to Confer Retinoid Resistance on Breast Cancer Cells

Retinoic acid (RA) and its synthetic derivatives, retinoids, have been established as promising anticancer agents based on their ability to regulate cell proliferation and survival. Clinical trials, however, have revealed that cancer cells often acquire resistance to retinoid therapy. Therefore, elucidation of underlying mechanisms of retinoid resistance has been considered key to developing more effective use of retinoids in cancer treatment. In this study, we show that constitutive activation of ERK MAP kinase signaling, which is often caused by oncogenic mutations in RAS or RAF genes, suppresses RA receptor (RAR) signaling in breast cancer cells. We show that activation of the ERK pathway suppresses, whereas its inhibition promotes, RA-induced transcriptional activation of RAR and the resultant upregulation of RAR-target genes in breast cancer cells. Importantly, ERK inhibition potentiates the tumor-suppressive activity of RA in breast cancer cells. Moreover, we also reveal that suppression of RAR signaling and activation of ERK signaling are associated with poor prognoses in breast cancer patients and represent hallmarks of specific subtypes of breast cancers, such as basal-like, HER2-enriched and luminal B. These results indicate that ERK-dependent suppression of RAR activity underlies retinoid resistance and is associated with cancer subtypes and patient prognosis in breast cancers

Identification of Aging-Associated Gene Expression Signatures That Precede Intestinal Tumorigenesis.

Aging-associated alterations of cellular functions have been implicated in various disorders including cancers. Due to difficulties in identifying aging cells in living tissues, most studies have focused on aging-associated changes in whole tissues or certain cell pools. Thus, it remains unclear what kinds of alterations accumulate in each cell during aging. While analyzing several mouse lines expressing fluorescent proteins (FPs), we found that expression of FPs is gradually silenced in the intestinal epithelium during aging in units of single crypt composed of clonal stem cell progeny. The cells with low FP expression retained the wild-type Apc allele and the tissues composed of them did not exhibit any histological abnormality. Notably, the silencing of FPs was also observed in intestinal adenomas and the surrounding normal mucosae of Apc-mutant mice, and mediated by DNA methylation of the upstream promoter. Our genome-wide analysis then showed that the silencing of FPs reflects specific gene expression alterations during aging, and that these alterations occur in not only mouse adenomas but also human sporadic and hereditary (familial adenomatous polyposis) adenomas. Importantly, pharmacological inhibition of DNA methylation, which suppresses adenoma development in Apc-mutant mice, reverted the aging-associated silencing of FPs and gene expression alterations. These results identify aging-associated gene expression signatures that are heterogeneously induced by DNA methylation and precede intestinal tumorigenesis triggered by Apc inactivation, and suggest that pharmacological inhibition of the signature genes could be a novel strategy for the prevention and treatment of intestinal tumors