Abstract 923: Human embryonic stem cells exhibit altruistic cell death that release death signals having potent anti-cancer activity
Bibliographic record
Abstract
Abstract Background: We recently described the altruistic stem cell (ASC) phenotype in human embryonic stem cells (hESCs) as well as in mesenchymal stem cells (1, 2). The ASC phenotype was characterized by altered state of p53/MDM2 feedback system that permitted the cells to transiently acquire an unstable state of low p53 allowing the cells to survive in extreme microenvironment (1). Interestingly, we noted that ASCs spontaneously returned to its basal state of high p53 after a period of two weeks (1, 2). In this study, we speculate that this return of p53 levels to basal state could be a safety mechanism to prevent malignant transformation of ASCs. We also speculate that ASCs may release soluble factors like high mobility group protein B1 (HMGB-1) that could selectively target the cells exhibiting abnormal p53 e.g. cancer cells. Here, we further characterized ASC phenotype and its fate. Methods: hESC, BG01 cells were exposed to extreme hypoxia followed by reoxygenation and then ABCG2+/SSEA3+ cells were flow cytometry sorted. This specific subpopulation is enriched in ASCs and could be cultured in vitro for two weeks (1). The post- hypoxia treated ABCG2+/SSEA3+ cells were maintained in serum free media, and subjected to apoptosis, and senescence assays. The conditioned media (CM) of these cells and subjected to HMGB-1 measurement by ELISA. To measure bystander apoptosis, teratocarcinoma cells (Tera-2) were treated with the CM followed by measurement of apoptosis. Results: Here we confirmed that p53 and MDM2 in ABCG2+/SSEA3+ cells exhibited return of oscillation between days 19-24. This was associated increase in apoptosis, and senescence of these cells. Apoptosis/senescence was decreased when treated with either Pifithrin α, an inhibitor of p53, or by siRNA silencing of p53, suggesting p53-dependent apoptosis. Additionally, treatment with Nutlin-3, an inhibitor of MDM2 (1) led to a 10-fold increase in apoptosis indicating that high MDM2 was required to prevent the apoptosis of ASCs. Thus, ASCs underwent spontaneous apoptosis (altruistic cell death) due to the return of p53/MDMD2 oscillation. We suggest that this return of p53 and associated apoptosis could be a safety mechanism to prevent malignant transformation of ASCs. Next, we found that the CM of ABCG2+/SSEA3+ cells contained high levels of HMGB-1 compared to the parental BG01 cells. Importantly, CM treatment led to p53 dependent apoptosis of Tera-2 cells. Furthermore, CM treatment also inhibited the growth of Tera-2 xenografts in NOD/SCID mice. Conclusion: Our results indicate that ASCs undergoes altruistic cell death, and releases death signal mediated by HMGB1 that can target neighboring cells exhibiting abnormal p53 including cancer cells. We suggest that this unique property of ASCs could be exploited as a novel cancer therapeutic. 1. Das B et al, Stem Cells, 2012; 30(8):1685-95. 2. Pal B et al, Cancer Research, 2016; Volume 76, Issue 14 Supplement, pp. 251 Note: This abstract was not presented at the meeting. Citation Format: Bidisha Pal, Seema Bhuyan, Jaishree Garhyan, Herman Yeger, Bikul Das. Human embryonic stem cells exhibit altruistic cell death that release death signals having potent anti-cancer activity [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 923. doi:10.1158/1538-7445.AM2017-923
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.002 | 0.001 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".