A153 PYCRL LACTYLATION AS A POTENTIAL REGULATOR OF CANCER STEM CELL METABOLISM IN ESOPHAGEAL SQUAMOUS CELL CARCINOMA (ESCC)

Background

Patients with esophageal malignancy have a 5-year survival rate of only 14% in Canada. This high mortality rate is due to three factors: late diagnosis, difficulty in surgically removing the tumor because of its localization, and treatment resistance. Resistance can be developed after prolonged exposure to anti-cancer drugs and/or radiation. Indeed 30% of patients will not respond to treatment or will relapse. Resistance has been mainly ascribed to the presence of cancer stem cells (CSCs) inside the tumor. However, no treatment specifically directed against CSCs is available to patients.

Purpose

Thus, targeting CSCs is a promising strategy to improve the survival of patients with esophageal squamous cell carcinoma (ESCC), the most common type of esophageal cancer worldwide. Therefore, a better understanding of the molecular mechanisms occurring during long-term exposure to cancer treatments is imperative.

Method

Herein, we developed an unbiased approach to identify new players in chemotherapy and radiotherapy resistance development in ESCC. We established radio- (R), chemo- (C), and radiochemo-resistant (RC) human ESCC cell lines using prolonged exposure to radiation and/or chemotherapeutic agent 5-FU, respectively.

Result(s)

The enrichment in CSCs in all treated cell lines was demonstrated by an increase of ALDH1^high cells and CD24^high/CD44^high cells in flow cytometry. We then used a proteomic approach to identify new players in treatment resistance. Interestingly, pathway analysis pointed out to alterations in energy metabolism as well as amino acid metabolism. Seahorse assays showed that resistant cell lines have a lower respiration rate than control cells, while glycolysis remains unchanged. To further characterize these metabolic changes, we performed an unbiased metabolomic study and confirmed a decrease in amino acid levels such as proline, in resistant cell lines. Recently, metabolic regulation has been linked to a new post-translational modification, lactylation. Proteomic data were re-analyzed looking for lactylated protein and found, amongst others, PYCRL, an enzyme implicated in proline biosynthesis, as one of the most differentially lactylated proteins in treated cell lines compared to control. PYCRL lactylation was confirmed using immuno-fluorescence colocalization and immuno-precipitation. Lastly, using AlphaFold, preliminary results point toward the importance of PYCRL lactylation impairing PYCRL homomultimerization.

Conclusion(s)

To conclude, our results suggest an important role of proline metabolism following long-term treatment in ESCC. This study is a first step toward the identification of new targets to fight treatment resistance in ESCC patients.

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CAG, CIHR, Other

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Disclosure of Interest

None Declared

A16 ESOPHAGEAL ORGANOID PROLIFERATION AND DIFFERENTIATION ARE ALTERED BY LOSS OF MSH2

Background

The stratified epithelium of the esophagus includes Krt15+ basal stem cells that display self-renewing and regenerative capacity, and multipotency. However, the mechanisms that specifically control their functions remain unknown. Interestingly, RNA sequencing and GSEA revealed an enrichment of a gene set associated with DNA repair in Krt15+ cells vs Krt15- cells. We also observed that Msh2 (DNA mismatch repair pathway) is the most significantly upregulated gene in Krt15+ stem cells.

Aims

To determine the effect of Msh2 loss on self-renewal and differentiation of esophageal organoids.

Methods

Esophageal epithelial cells were isolated from a wild-type mouse. Using flow cytometry, esophageal Krt15+ (GFP+) and Krt15- (GFP-) cells were sorted from Krt15-CrePR1 (R26^mT/mG) mice. All cell populations were grown as organoids and Msh2 was depleted using a CRISPR/Cas9 approach. Impact of Msh2 loss on self-renewal and differentiation in esophageal epithelial organoids was evaluated through organoid formation assays, WST-1 proliferation assays and histological analysis.

Results

At baseline, organoids depleted for Msh2 formed more poorly differentiated and less well-differentiated organoids than controls. Lower expression of differentiation gene Krt13 was also observed in Msh2-depleted organoids, confirming an altered differentiation pattern. Furthermore, these organoids showed a higher organoid formation rate and proliferation by WST-1 assay, suggesting that self-renewal capacity and viability are increased when Msh2 is depleted. Interestingly, following radiation, organoids depleted for Msh2 showed higher residual levels of p-H2AX (DNA damage marker), suggesting that their capacity to cope with DNA damages is altered. As mentioned above, we previously reported that Msh2 is the most upregulated gene in Krt15+ vs Krt15- cells. Therefore, to determine if Msh2 role is distinct in both populations, we depleted Msh2 in Krt15+ and Krt15- cells-derived organoids. Interestingly, our preliminary results suggest that Msh2 deletion led to increased p-H2AX and decreased Krt13 levels in Krt15+ organoids but not in Krt15- organoids.

Conclusions

Our results show that Msh2 is potentially a key contributor of esophageal stemness in homeostatic and injured conditions.

Funding Agencies

CIHRCanada Research Chair

A17 TRP53 REGULATES ESLF-RENEWAL AND CELL DIFFERENTIATION IN KRT15+ INTESTINAL STEM CELLS

Background

Different pools of stem cells assure the intestinal epithelium homeostasis and regeneration. We recently reported that Krt15+ intestinal cells harbor self-renewal, multipotent and regenerative capacities, characteristics consistent with a stem cell population. p53 has been associated with the development of various types of cancer, and recent studies suggested it also regulates adult stem cell behavior in some tissues. However, its role in the maintenance of intestinal stem cells has not been explicitly covered. Therefore, we hypothesize that Trp53 loss specifically in Krt15+ intestinal stem cells will perturb the epithelial homeostasis and differentiation.

Aims

Identify the role of Trp53 in the regulation of intestinal stem cell and intestinal homeostasis

Methods

To induce Trp53 loss specifically in Krt15+ cells, we generated Krt15 CrePR1;Trp53fl/fl ( Krt15△Trp53) mice and induced Cre recombination by injecting RU486 (PR agonist). Mice were euthanized after Cre recombination at different time points. Organoid cultures were established from control and experimental mice.

Results

Two-month post Cre recombination, we observed no major morphological changes in the intestinal epithelium. However, we observed that crypts isolated from Krt15△Trp53 mice died rapidly and had difficulties forming organoids. When hyperactivating the Wnt/beta-catenin pathway through CHIR treatment, we observed that budding capacity was maintained in experimental organoids while control organoids formed mainly cysts as expected. We also observed an increased in Paneth cell-specific genes, suggesting an enrichment in Paneth cells. Interestingly, the expression of EpHB2 receptor and its target genes was decreased in organoids derived from Krt15△Trp53 mice. Ephrin signaling plays a crucial role in intestinal homeostasis by regulating cell position and migration, and previous studies suggest that ephrin receptors are a target of p53. Indeed, twelve-month post Cre recombination, altered architecture of crypt and villi was noted in the small intestinal epithelium of Krt15△Trp53 mice. Differentiation towards secretory cell types, specifically Paneth, goblet, and tuft cells, are significantly increased in Krt15△Trp53 mice. Interestingly, we also observed crypt cells expressing both goblet and Paneth cell markers suggesting dysfunction in the cell fate decision. Finally, decreased Notch pathway activation was also observed supporting that Trp53 loss, specifically in Krt15+ cells, leads to a dysregulation of secretory cell fate.

Conclusions

Loss of Trp53 specifically in Krt15+ cells affects the small intestinal homeostasis and secretory cell differentiation. Decreased Notch and ephrin signaling support the possible role of Trp53 in cell fate decision and self-renewal.

Funding Agencies

None

A3 TARGETING PROLINE METABOLISM TO OVERCOME TREATMENT RESISTANCE IN ESOPHAGEAL CANCER

Background

Patients with esophageal malignancy have a 5-year survival rate of only 14% in Canada. This high mortality rate is due to three factors: late diagnosis, difficulty to surgically remove the tumor due to its localization and treatment resistance. Treatment resistance has been ascribed to the presence of cancer stem cells (CSCs) inside the tumor. However, no treatment specifically directed against CSCs is available to patients. Therefore, targeting CSCs is a promising strategy to improve survival of patients with esophageal squamous cell carcinoma (ESCC), the most common type of esophageal cancer worldwide.

Aims

Herein, we developed an unbiased approach to identify new players in chemotherapy and radiotherapy resistance in ESCC.

Methods

We established radioresistant (RR), chemoresistant (CR) and radiochemoresistant (RCR) human ESCC cell lines using weekly radiation and/or continuous treatment with increasing doses of chemotherapeutic agent 5-FU. We validated that the process of resistance acquisition correlates with enrichment in CSCs as revealed by higher ALDH1 expression, and increased proportion of ALDH1^high cells and CD24^high/CD44^high cells in flow cytometry. We then used a proteomic approach to identify new players in treatment resistance.

Results

Interestingly, pathway analysis demonstrated enrichment in energy metabolism as well as amino acid metabolism. Seahorse assays showed a more quiescent metabolism in all three types of resistant cells compared to the control cell line. More precisely, resistant cell lines have a lower respiration rate than control cell line, while glycolysis remains unchanged. Surprisingly, our results show a metabolic rewiring very different from the well-known Warburg effect. To further characterise these metabolic changes, we performed an unbiased metabolomic pilot study and confirmed a decrease in amino acid levels such as proline, in resistant cell lines. Preliminary data show that when cultured in DMEM with proline addition, CD44^high/CD24^high cell proportion is decreased in control and RR cell lines suggesting that proline is a key regulator of CSC population in ESCC.

Conclusions

To conclude, our results suggest an important role of metabolism in ESCC treatment resistance. This study is a first step towards the identification of new targets to fight treatment resistance in ESCC patients.

Funding Agencies

CAG, CIHRCanada research chair TIER 2

A27 MSH2 CONTRIBUTES TO SELF-RENEWAL OF ESOPHAGEAL ORGANOIDS

Background

The esophagus is lined by a stratified epithelium in which basal cells can proliferate and undergo differentiation while migrating towards the lumen. In the basal layer, we also find Krt15+ stem cells that are multipotent, self-renewing and that have regenerative capacity. However, mechanisms that specifically control their functions remain unknown. Interestingly, RNA sequencing and gene set enrichment analysis (GSEA) revealed an enrichment of a gene set associated with DNA repair in Krt15+ cells in comparison to Krt15- cells. We also observed that Msh2 (MutS homolog 2), a gene associated with the DNA mismatch repair (MMR) mechanism, is the most significantly upregulated gene in Krt15+ stem cells.

Aims

To determine the impact of Msh2 loss on self-renewal of esophageal organoids under normal and stress conditions.

Methods

Esophageal epithelial cells were isolated from a wild type mouse and grown as organoids, a 3D culture model that supports stem cell growth and morphologically reproduces the tissue of origin. To determine Msh2 role in esophageal epithelium, this gene was deleted through a CRISPR/Cas9 approach in mouse esophageal organoids. Invalidation was confirmed by Western Blot and immunofluorescence. Impact of Msh2 loss on self-renewal was measured under normal condition and following radiation.

Results

At baseline, loss of Msh2 decreases the organoid formation rate of esophageal organoids. Furthermore, following high-dose radiation, Msh2 deficient cells form less organoids than control cells. These results suggest that self-renewal capacity is reduced when Msh2 is depleted. Interestingly, following radiation, organoids depleted for Msh2 show higher residual levels of p-H2AX, a DNA damage marker, and p-ATM, a key kinase in DNA damage response, suggesting that their capacity to cope with DNA damages is reduced.

Conclusions

Our results suggest that Msh2 contributes to maintaining genomic integrity in esophageal cells and that contributes to maintaining self-renewal capacity of basal cells and possibly esophageal stem cells.

Funding Agencies

Canada Research Chair.

A149 TRP53 LOSS IN KRT15+ INTESTINAL STEM CELLS SEVERELY AFFECTS SECRETORY CELL FATE AND SELF-RENEWAL

Background

Intestinal epithelium homeostasis is maintained by two main populations of stem cells: Lgr5+ and reserve stem cells. Under injury, cell plasticity has been observed in progenitor and differentiated cells. We recently reported that Krt15+ cells are present in small intestinal and colon epithelia, and harbor self-renewal, multipotent and regenerative capacities. As in Lgr5+and reserve stem cells, hyperactivation of Wnt/b-catenin pathway in Krt15+ stem cells lead to tumor formation in the intestinal epithelium. While these intestinal stem cell populations can act as tumor-initiating cells in sporadic colon cancer, little is known about the cell-of-origin of colitis-associated colon cancer (CAC). TP53 alteration is reported as an early event in CAC. Therefore, we hypothesize that Trp53 loss specifically in Krt15+ stem cells will perturb the epithelial homeostasis and lead to tumor formation.

Aims

Identify if Krt15+ cells may act as the cell-of-origin in colitis-associated colorectal cancer

Methods

To induce Trp53 loss specifically in Krt15+ cells, we generated Krt15-CrePR1;Trp53fl/fl (Krt15△Trp53) mice, induced Cre recombination by injecting RU486 (PR agonist) and euthanized the mice at different time points following recombination.

Results

Results

Twelve-month following Cre recombination, adenoma formation was observed in a small proportion of Krt15△Trp53 mice. Though, Trp53 loss in Krt15+ cells severely perturbed the small intestinal morphology in every mouse studied. Increased crypt length and villi width was observed in Krt15△Trp53 vs control mice without any changes in cell proliferation. We also observed an increased number of Tuft cells and goblet cells in the villi of experimental mice. In the crypt, higher number of Paneth cells and aberrant presence of goblet cells were noted in Krt15△Trp53mice. Interestingly, we also observed crypt cells expressing goblet and Paneth cell markers and decreased Notch pathway activation suggesting dysregulation of secretory cell fate. Krt15△Trp53 mice display higher number of fibroblasts in the villi and the submucosa, as well as thickening of the muscularis layer. Interestingly, similar observations (accumulation of secretory cells and fibrosis) have been reported in IBD patients, supporting the possible role of Krt15+ cells in CAC. Furthermore, crypts isolated from Krt15△Trp53 mice rapidly die when seeded as organoids vs crypts from control mice, suggesting that the alterations observed in vivo in Paneth cells might interfere with the stem cell niche and therefore reduce self-renewal of Krt15+ cells.

Conclusions

Trp53 loss specifically in Krt15+ cells impaired cell fate decision, induced secretory cell hyperplasia, affected self-renewal ability, and initiated adenoma formation supporting the possible role of Krt15+ cells in gut inflammation and cancer.

Funding Agencies

Canada Research Chair, Cancer Research Society, CFI