Deubiquitylation of Rab35 by USP32 promotes the transmission of imatinib resistance by enhancing exosome secretion in gastrointestinal stromal tumours.

Imatinib is a tyrosine kinase inhibitor that is widely used to combat gastrointestinal stromal tumours (GISTs). However, secondary resistance to imatinib is an important challenge in GIST treatment. Recent studies have demonstrated that cancer-derived nanosized exosomes play a key role in intercellular communication, but little is known about the roles of exosomes in imatinib-resistant GISTs. Here, we reveal that exosomes released from imatinib-resistant GISTs transmit drug resistance to imatinib-sensitive tumours. By using iTRAQ technology, we demonstrate that Ras-related protein Rab-35 (Rab35) is upregulated differentially in imatinib-resistant GISTs. Loss of Rab35 decreases exosome secretion, thereby hampering the transmission of imatinib resistance to sensitive tumours. Mechanistically, we showed that the ubiquitin‒proteasome system is involved in elevated Rab35 expression and that ubiquitin-specific protease 32 (USP32), a deubiquitylating enzyme, is bound to Rab35. Further experiments demonstrate that this protease protects Rab35 from proteasomal degradation by reducing Lys48 (K48)-ubiquitination. Additionally, we found that the transcription factor ETV1, which is a lineage survival factor in GISTs, promotes USP32 expression. Collectively, our results reveal that exosomes transmit imatinib resistance in GISTs and that deubiquitylation plays a key role in regulating the transmission process. The USP32-Rab35 axis provides a potential target for interventions to reduce the occurrence of imatinib resistance in GISTs.

N6-methyladenosine-modified USP13 induces pro-survival autophagy and imatinib resistance via regulating the stabilization of autophagy-related protein 5 in gastrointestinal stromal tumors.

Secondary resistance to imatinib (IM) represents a major challenge for therapy of gastrointestinal stromal tumors (GISTs). Aberrations in oncogenic pathways, including autophagy, correlate with IM resistance. Regulation of autophagy-related protein 5 (ATG5) by the ubiquitin-proteasome system is critical for autophagic activity, although the molecular mechanisms that underpin reversible deubiquitination of ATG5 have not been deciphered fully. Here, we identified USP13 as an essential deubiquitinase that stabilizes ATG5 in a process that depends on the PAK1 serine/threonine-protein kinase and which enhances autophagy and promotes IM resistance in GIST cells. USP13 preferentially is induced in GIST cells by IM and interacts with ATG5, which leads to stabilization of ATG5 through deubiquitination. Activation of PAK1 promoted phosphorylation of ATG5 thereby enhancing the interaction of ATG5 with USP13. Furthermore, N6-methyladenosine methyltransferase-like 3 (METTL3) mediated stabilization of USP13 mRNA that required the m6A reader IGF2BP2. Moreover, an inhibitor of USP13 caused ATG5 decay and co-administration of this inhibitor with 3-methyladenine boosted treatment efficacy of IM in murine xenograft models derived from GIST cells. Our findings highlight USP13 as an essential regulator of autophagy and IM resistance in GIST cells and reveal USP13 as a novel potential therapeutic target for GIST treatment.

METTL3-Mediated ADAMTS9 Suppression Facilitates Angiogenesis and Carcinogenesis in Gastric Cancer.

The role of methyltransferase-like 3 (METTL3), which participates in catalyzing N-methyladenosine (m6A) RNA modification, in gastric cancer (GC) is unclear. Here, we found that METTL3 was overexpressed in human GC. Functionally, we verified that METTL3 promoted tumor cell proliferation and angiogenesis through a series of phenotypic experiments. Subsequently, ADAMTS9 was identified as the downstream effector of METTL3 in GC, which could be degraded by the YTHDF2-dependent pathway. Finally, the data suggested that METTL3 might facilitate GC progression through the ADAMTS9-mediated PI3K/AKT pathway. Our study unveiled the fundamental mechanisms of METTL3 in GC progression. The clinical value of METTL3 in GC deserves further exploration.

Substrate rigidity dictates colorectal tumorigenic cell stemness and metastasis via CRAD-dependent mechanotransduction.

Tumor physical microenvironment contributes greatly to the response of tumor cells. However, the mechanism of how extracellular substrate rigidity remodels colorectal cancer (CRC) cell fate and affects CRC progression remains elusive. Here, we show that F-actin regulator KIAA1211, also known as Capping protein inhibiting regulator of actin dynamics (CRAD), negatively correlates with CRC progression, stemness, and metastasis. Mechanistically, decreased CRAD in soft substrates induces Yes-associated protein (YAP) retention in the cytoplasm, restoring the repression effect on stemness markers NANOG and OCT4, thereby promoting CRC stemness and metastasis. Furthermore, CRAD deficiency promotes colorectal tumor cell softening and regulates epithelial-mesenchymal transition (EMT) states, contributing to its metastasis potential. Clinically, CRAD expression is correlated with malignant degrees and metastasis in CRC patients. Our work uncovers a role of CRAD in anticancer and mechanical signal transduction of the extracellular matrix in CRC.

N6-methyladenosine modification regulates imatinib resistance of gastrointestinal stromal tumor by enhancing the expression of multidrug transporter MRP1.

N6-methyladenosine (m6A) is a frequently occurring mRNA modification, which regulates mRNA stability, splicing, and translation. However, its role in drug resistance of gastrointestinal stromal tumor (GIST) is not known. Here, we report that m6A modification levels are elevated in imatinib-resistant GIST cells and tissues, and that methyltransferase METTL3 is one of the main protein responsible for this aberrant modification. Increased METTL3 levels contributed to imatinib resistance and worse progression-free survival of GIST patients. Mechanistic studies revealed that METTL3-mediated m6A modification of the 5'UTR of the multidrug transporter MRP1 mRNA promoted drug resistance of GIST by stimulating MRP1 mRNA translation, via binding with YTHDF1 and eEF-1. Further, METTL3 transcription in imatinib resistant GIST cells was activated by ETV1, leading to the increased m6A methylation of MRP1 mRNA. This is the first report showing a novel regulatory mechanism whereby ETV1, METTL3, and the YTHDF1/eEF-1 complex mediate the translation of MRP1 mRNA in an m6A-dependent manner to regulate the intracellular concentration of imatinib and drug resistance of GIST. These findings highlight MRP1 as a new potential therapeutic target for imatinib resistance of GIST.

HIF-1α regulates cellular metabolism, and Imatinib resistance by targeting phosphogluconate dehydrogenase in gastrointestinal stromal tumors.

The pentose phosphate pathway (PPP) plays a critical role in maintaining cellular redox homeostasis in tumor cells and macromolecule biosynthesis. Upregulation of the PPP has been shown in several types of tumor. However, how the PPP is regulated to confer selective growth advantages on drug resistant tumor cells is not well understood. Here we show a metabolic shift from tricarboxylic acid cycle (TCA) to PPP after a long period induction of Imatinib (IM). One of the rate-limiting enzymes of the PPP-phosphogluconate dehydrogenase (PGD), is dramatically upregulated in gastrointestinal stromal tumors (GISTs) and GIST cell lines resistant to Imatinib (IM) compared with sensitive controls. Functional studies revealed that the overexpression of PGD in resistant GIST cell lines promoted cell proliferation and suppressed cell apoptosis. Mechanistic analyses suggested that the protein level of hypoxia inducible factor-1α (HIF-1α) increased during long time stimulation of reactive oxygen species (ROS) produced by IM. Importantly, we further demonstrated that HIF-1α also had positive correlation with PGD, resulting in the change of metabolic pathway, and ultimately causing drug resistance in GIST. Our findings show that long term use of IM alters the metabolic phenotype of GIST through ROS and HIF-1α, and this may contribute to IM resistance. Our work offers preclinical proof of metabolic target as an effective strategy for the treatment of drug resistance in GIST.

HMGA1 Regulates the Stem Cell-Like Properties of Circulating Tumor Cells from GIST Patients via Wnt/ß-Catenin Pathway.

BACKGROUND: Gastrointestinal stromal tumor (GIST) is the most common sarcoma of the digestive system. Circulating tumor cells (CTCs) have been proven to be critical in the recurrence and metastasis of diseases; however, the characteristics of CTCs of GIST are still unclear. METHODS: We sorted out and verified the validity of CTCs from peripheral blood of gastrointestinal stromal tumor (GIST) patients with or without heterochronous liver metastasis using flow cytometry (FCM). Differential genes were analyzed between the GIST patients with and without liver metastasis using next-generation sequencing (NGS). RESULTS: The preliminary study on the characteristics of CTCs revealed that CTCs of GIST patients with heterochronous liver metastasis had stronger stem cell-like properties (SC-like properties) than CTCs of those without liver metastasis. Furthermore, NGS followed with a series of assays revealed that HMGA1 played a critical role in regulating the SC-like properties of CTCs. Mechanistically, HMGA1 could activate Wnt/ß-catenin pathway in vitro and vivo. Moreover, we found that the expression level of HMGA1 in CTCs was an independent risk factor probably influencing the prognosis of GIST patients. CONCLUSION: Our findings indicate the significant role of HMGA1 in SC-like properties, IM resistance and eventually hepatic metastasis formation of CTCs. Targeting HMGA1 in CTCs may be a therapeutic strategy for GIST patients with hepatic metastasis.

Circulating tumor cells in whole process management of gastrointestinal stromal tumor in a real-life setting.

BACKGROUND/AIM: Liquid biopsy is changing the diagnosis and treatment strategies of various neoplasms. However, the circulating tumor cells (CTCs) of gastrointestinal stromal tumor (GIST) patients with different disease process are not clear. To better understand the dynamic change of CTCs in GIST patients, we conducted a real-life setting study. PATIENTS AND METHODS: One-hundred fifty GIST patients were included. The isolation by size of tumor cell (ISET) method was employed to detect the CTCs/circulating tumor microemboli (CTM). Imatinib (IM) plasma concentration was detected by liquid chromatography-mass spectrometry/mass spectrometry (LC-MS/MS). Multivariate and univariate analysis were used to analyze the effects of clinical characteristics on the positive rate of CTC and the number of CTCs/CTM. RESULTS: The positive rate of CTCs was 72%. The median number of CTCs and CTM was 4 and 0. Logistic multivariate regression analysis showed that tumor diameter was the only independent factor of the positive rate of CTCs (P < 0.05). The numbers of CTCs and CTM had intensive linear correlation (P < 0.001). Tumor diameter, Ki 67 expression and mitotic were related to the number of CTCs (P < 0.05). Patients with higher Ki 67 expression tend to have more CTM (P < 0.05). IM plasma concentration showed no influence to the CTCs/CTM (P > 0.05). CONCLUSIONS: : In the current study, we assessed the CTCs and CTM of GIST patients in various disease progressions and identified clinicopathological factors influencing the detection of CTCs and CTM. These results are instructive for clinicians to understand CTCs/CTM in GIST patients.