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Calcium Signaling Is Impaired in PTEN-Deficient T Cell Acute Lymphoblastic Leukemia
Saran Pankaew1,2, Delphine Potier1, Clémence Grosjean1
1Aix Marseille Univ, CNRS, INSERM, CIML, Marseille, France.
Abstract:
PTEN (Phosphatase and TENsin homolog) is a well-known tumor suppressor involved in numerous types of cancer, including T-cell acute lymphoblastic leukemia (T-ALL). In human, loss-of-function mutations of PTEN are correlated to mature T-ALL expressing a T-cell receptor (TCR) at their cell surface. In accordance with human T-ALL, inactivation of Pten gene in mouse thymocytes induces TCRαβ+ T-ALL development. Herein, we explored the functional interaction between TCRαβ signaling and PTEN. First, we performed single-cell RNA sequencing (scRNAseq) of PTEN-deficient and PTEN-proficient thymocytes. Bioinformatic analysis of our scRNAseq data showed that pathological Ptendel thymocytes express, as expected, Myc transcript, whereas inference of pathway activity revealed that these Ptendel thymocytes display a lower calcium pathway activity score compared to their physiological counterparts. We confirmed this result using ex vivo calcium flux assay and showed that upon TCR activation tumor Ptendel blasts were unable to release calcium ions (Ca2+) from the endoplasmic reticulum to the cytosol. In order to understand such phenomena, we constructed a mathematical model centered on the mechanisms controlling the calcium flux, integrating TCR signal strength and PTEN interactions. This qualitative model displays a dynamical behavior coherent with the dynamics reported in the literature, it also predicts that PTEN affects positively IP3 (inositol 1,4,5-trisphosphate) receptors (ITPR). Hence, we analyzed Itpr expression and unraveled that ITPR proteins levels are reduced in PTEN-deficient tumor cells compared to physiological and leukemic PTEN-proficient cells. However, calcium flux and ITPR proteins expression are not defective in non-leukemic PTEN-deficient T cells indicating that beyond PTEN loss an additional alteration is required. Altogether, our study shows that ITPR/Calcium flux is a part of the oncogenic landscape shaped by PTEN loss and pinpoints a putative role of PTEN in the regulation of ITPR proteins in thymocytes, which remains to be characterized.
Insights
PTEN loss in T-ALL impairs calcium signaling by reducing inositol trisphosphate receptors (ITPRs). This defect is crucial for T-cell acute lymphoblastic leukemia development, highlighting PTEN
Area of Science:
- Oncology
- Immunology
- Cell Biology
Background:
- PTEN is a critical tumor suppressor gene implicated in various cancers, including T-cell acute lymphoblastic leukemia (T-ALL).
- Loss-of-function mutations in PTEN are associated with mature T-ALL expressing T-cell receptors (TCRs).
- Pten inactivation in mouse thymocytes recapitulates human T-ALL, leading to TCRαβ+ T-ALL.
Purpose of the Study:
- To investigate the functional interplay between TCR signaling and PTEN in T-ALL pathogenesis.
- To elucidate the role of PTEN in regulating calcium flux and its downstream effectors in thymocytes.
- To identify potential therapeutic targets by understanding the PTEN-TCR-calcium signaling axis.
Main Methods:
- Single-cell RNA sequencing (scRNAseq) of PTEN-deficient and PTEN-proficient thymocytes.
- Bioinformatic analysis to infer pathway activity, focusing on calcium signaling.
- Ex vivo calcium flux assays to measure intracellular calcium ion (Ca2+) release.
- Mathematical modeling of calcium flux mechanisms integrating TCR signaling and PTEN interactions.
- Analysis of inositol 1,4,5-trisphosphate receptor (ITPR) expression at the mRNA and protein levels.
Main Results:
- PTEN-deficient thymocytes exhibited reduced Myc transcript levels and significantly lower calcium pathway activity compared to PTEN-proficient cells.
- Ex vivo assays confirmed that PTEN-deficient T-ALL cells are unable to release Ca2+ from the endoplasmic reticulum upon TCR activation.
- Mathematical modeling predicted a positive regulatory role of PTEN on ITPR activity.
- Reduced ITPR protein levels were observed in PTEN-deficient T-ALL cells, correlating with impaired calcium flux.
- Normal calcium flux and ITPR expression in non-leukemic PTEN-deficient T cells suggest that additional alterations are necessary for T-ALL development.
Conclusions:
- PTEN loss contributes to T-ALL oncogenesis by disrupting the ITPR/calcium flux pathway.
- PTEN positively regulates ITPR expression/function in thymocytes, impacting calcium homeostasis.
- Impaired calcium signaling due to PTEN deficiency is a key feature of T-ALL, but requires cooperating events for leukemogenesis.
- PTEN's role in regulating ITPR protein levels in thymocytes warrants further investigation.
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