Multilineage differentiation of cloned HRA-19 cells in serum-free medium: a model of human colorectal epithelial differentiation

Molecular glue triggers degradation of PHGDH by enhancing the interaction between DDB1 and PHGDH

Cancer stem cells (CSCs) play a pivotal role in tumor initiation, proliferation, metastasis, drug resistance, and recurrence. Consequently, targeting CSCs has emerged as a promising avenue for cancer therapy. Recently, 3-phosphoglycerate dehydrogenase (PHGDH) has been identified as being intricately associated with the regulation of numerous cancer stem cells. Yet, reports detailing the functional regulators of PHGDH that can mitigate the stemness across cancer types are limited. In this study, the novel "molecular glue" LXH-3-71 was identified, and it robustly induced degradation of PHGDH, thereby modulating the stemness of colorectal cancer cells (CRCs) both in vitro and in vivo. Remarkably, LXH-3-71 was observed to form a dynamic chimera, between PHGDH and the DDB1-CRL E3 ligase. These insights not only elucidate the anti-CSCs mechanism of the lead compound but also suggest that degradation of PHGDH may be a more viable therapeutic strategy than the development of PHGDH inhibitors. Additionally, compound LXH-3-71 was leveraged as a novel ligand for the DDB1-CRL E3 ligase, facilitating the development of new PROTAC molecules targeting EGFR and CDK4 degradation.

CSN6-TRIM21 axis instigates cancer stemness during tumorigenesis

Background

Cancer stem cells (CSCs) are responsible for tumour initiation, metastasis and recurrence. However, the mechanism of CSC formation, maintenance and expansion in colorectal cancer (CRC) remains poorly characterised.

Methods

The role of COP9 signalosome subunit 6 (CSN6) in regulating cancer stemness was evaluated by organoid formation and limited dilution analysis. The role of CSN6–TRIM21–OCT1–ALDH1A1 axis in CSC formation was evaluated in vitro and in vivo. The association of CSN6, TRIM21 and ALDH1A1 expression was validated by a tissue microarray with 267 CRC patients.

Results

The results showed that CSN6 is critical for sphere formation and maintaining the growth of patient-derived organoids (PDOs). We characterised the role of CSN6 in regulating cancer stemness, which involves the TRIM21 E3 ubiquitin ligase, transcription factor POU class 2 homeobox 1 (OCT1) and cancer stem cell marker aldehyde dehydrogenase 1 A1 (ALDH1A1). Our data showed that CSN6 facilitates ubiquitin-mediated degradation of TRIM21, which in turn decreases TRIM21-mediated OCT1 ubiquitination and subsequently stabilises OCT1. Consequently, OCT1 stabilisation leads to ALDH1A1expression and promotes cancer stemness. We further showed that the protein expression levels of CSN6, TRIM21 and ALDH1A1 can serve as prognostic markers for human CRC.

Conclusions

In conclusion, we validate a pathway for cancer stemness regulation involving ALDH1A1 levels through the CSN6–TRIM21 axis, which may be utilised as CRC molecular markers and be targeted for therapeutic intervention in cancers.

Stem cell dynamics in homeostasis and cancer of the intestine

Intestinal stem cells (ISCs) and colorectal cancer (CRC) biology are tightly linked in many aspects. It is generally thought that ISCs are the cells of origin for a large proportion of CRCs and crucial ISC-associated signalling pathways are often affected in CRCs. Moreover, CRCs are thought to retain a cellular hierarchy that is reminiscent of the intestinal epithelium. Recent studies offer quantitative insights into the dynamics of ISC behaviour that govern homeostasis and thereby provide the necessary baseline parameters to begin to apply these analyses during the various stages of tumour development.

A stochastic model for cancer stem cell origin in metastatic colon cancer

Human cancers have been found to include transformed stem cells that may drive cancer progression to metastasis. Here, we report that metastatic colon cancer contains clonally derived tumor cells with all of the critical properties expected of stem cells, including self-renewal and the ability to differentiate into mature colon cells. Additionally, when injected into mice, these cells initiated tumors that closely resemble human cancer. Karyotype analyses of parental and clonally derived tumor cells expressed many consistent (clonal) along with unique chromosomal aberrations, suggesting the presence of chromosomal instability in the cancer stem cells. Thus, this new model for cancer origin and metastatic progression includes features of both the hierarchical model for cancerous stem cells and the stochastic model, driven by the observation of chromosomal instability.

Alpha2beta1 integrin regulates lineage commitment in multipotent human colorectal cancer cells

The human colorectal epithelium is maintained by multipotent stem cells that give rise to absorptive, mucous, and endocrine lineages. Recent evidence suggests that human colorectal cancers are likewise maintained by a minority population of so-called cancer stem cells. We have previously established a human colorectal cancer cell line with multipotent characteristics (HRA-19) and developed a serum-free medium that induces endocrine, mucous and absorptive lineage commitment by HRA-19 cells in vitro. In this study, we investigate the role of the β1 integrin family of cell surface extracellular matrix receptors in multilineage differentiation by these multipotent human colorectal cancer cells. We show that endocrine and mucous lineage commitment is blocked in the presence of function-blocking antibodies to β1 integrin. Function-blocking antibodies to α2 integrin also blocked both HRA-19 endocrine lineage commitment and enterocytic differentiation by Caco-2 human colon cancer cells; both effects being abrogated by the MEK inhibitor, PD98059, suggesting a role for ERK signaling in α2-mediated regulation of colorectal cancer cell differentiation. To further explore the role of α2 integrin in multilineage differentiation, we established multipotent cells expressing high levels of wild-type α2 integrin or a non-signaling chimeric α2 integrin. Overexpression of wild-type α2 integrin in HRA-19 cells significantly enhanced endocrine and mucous lineage commitment, while cells expressing the non-signaling chimeric α2 integrin had negligible ability for either endocrine or mucous lineage commitment. This study indicates that the collagen receptor α2β1 integrin is a regulator of cell fate in human multipotent colorectal cancer cells.

Collagen IV synthesis is restricted to the enteroendocrine pathway during multilineage differentiation of human colorectal epithelial stem cells

The human large intestine is lined by a rapidly renewing epithelial monolayer where cell loss is precisely balanced with cell production. The continuous supply of new cells is produced by undifferentiated multipotent stem cells via a coordinated program of proliferation and differentiation yielding three epithelial lineages: absorptive, goblet and enteroendocrine. Cell-matrix interactions have been suggested to be regulators of the multilineage differentiation program of the colorectal crypt but the expression of matrix proteins or their receptors does not appear to have the subtlety expected for this task.

We have developed an in vitro model system of intestinal epithelial stem cells to facilitate the direct analysis of stem cells undergoing lineage commitment and differentiation. Using this culture system, we can now directly investigate the role of cell-matrix signalling in stem-cell decisions. In this study, collagen-IV synthesis has been followed in monolayers of multipotent cells that have been induced to differentiate into absorptive, goblet and enteroendocrine cells. Our experiments demonstrate that commitment to the enteroendocrine lineage is specifically accompanied by the expression of type-IV collagen that remains enteroendocrine-cell associated. Undifferentiated cells, absorptive cells and goblet cells do not express collagen IV. To confirm that the differential lineage-specific expression of collagen IV observed in the model system was representative of the in vivo situation, collagen-IV synthesis was analysed in isolated human colorectal crypts and tissue sections using immunocytochemistry and in situ hybridisation. These studies confirmed the in vitro findings, in that implementation of the enteroendocrine differentiation program involves synthesis and accumulation of a collagen-IV matrix. Thus, human colorectal enteroendocrine cells are unique in the colorectal crypt in that they assemble a cell-associated collagen-IV-rich matrix not observed on other colorectal epithelial cells.

This study provides the first evidence for differential matrix synthesis between colorectal epithelial lineages in human colorectal epithelium. The specialised pericellular environment of the enteroendocrine cells might explain some of the unique phenotypic characteristics of this cell lineage. Furthermore, these findings suggest a potential mechanism whereby individual epithelial cells could modulate their cell-matrix signalling even while rapidly migrating in heterogeneous sheets over a shared basement membrane.

Convergent effects of growth factors, hormones, and fibronectin are necessary for the enterocyte differentiation of a colon adenocarcinoma cell line (HT29-D4)

The aim of this work was to show in serum-free medium a convergent effect of physiological factors and extracellular matrix proteins on the differentiation process of enterocytes by taking as a model the HT29-D4 clone that has the feature of differentiating when subcultured in fetal bovine serum glucose-free medium. We show that triiodothyronine (T3) as well as insulin promotes limited cell growth and differentiation, whereas fibronectin or bovine serum albumin (BSA) induces cell growth and a low level of differentiation. However, insulin, T3, fibronectin, and BSA together with epidermal growth factor and transferrin promoted satisfactory growth and enterocyte morphology with epithelial electrophysiological properties in HT29-D4 cells. With these factors adequate protein targeting was achieved since cells apically expressed the carcinoembryonic antigen, and basolaterally transferrin and insulin receptors, beta 1 and alpha v beta 6 integrins, talin, vinculin, and focal adhesion kinase (FAK). Talin, vinculin, FAK, and alpha v beta 6 integrin, the fibronectin receptor, were clustered in focal contacts, which agrees with a possible role of fibronectin in final cell growth, the latter process mediating the final phase of differentiation. This level of differentiation can be maintained for a long time. Thus HT29-D4 cells appear to be a suitable model to study the implication of integrins in the differentiation process of human enterocytes.