Proinsulin C-peptide inhibits high glucose-induced migration and invasion of ovarian cancer cells

RSL3 sensitizes glioma cells to ionizing radiation by suppressing TGM2-dependent DNA damage repair and epithelial-mesenchymal transition

RAS-selective lethal small molecule 3 (RSL3) is a small-molecule compound that triggers ferroptosis by inactivating glutathione peroxidase 4. However, its effect on the radioresistance of glioma cells and the underlying mechanisms remains unclear. In this study, we found that RSL3 sensitized glioma cells to ionizing radiation (IR) and enhanced IR-induced DNA double-strand breaks (DSBs). Inhibition of ferroptosis pathways partly prevented the clonogenic death caused by the IR/RSL3 combination but did not alleviate the DNA DSBs, indicating that RSL3 promotes IR-induced DNA DSBs via a non-ferroptotic mechanism. We demonstrated that transglutaminase 2 (TGM2) plays a vital role in the radiosensitization effect of RSL3 on glioma cells. Treatment with RSL3 downregulated TGM2 in a dose-dependent manner. Overexpression of TGM2 not only alleviated DNA DSBs but also inhibited clonogenic death caused by the IR/RSL3 combination. Mechanistically, RSL3 triggered oxidative stress in glioma cells, which promoted the S-gluthathionylation of TGM2 via upregulation of glutathione S-transferase P1(GSTP1), culminating in the proteasomal degradation of TGM2. This process resulted in the suppression of DNA repair mechanisms by impeding the nuclear accumulation of TGM2 and disrupting the interaction between TGM2 and topoisomerase IIα after irradiation. We also found that RSL3 inhibited glioma cell epithelial-mesenchymal transition (EMT) in both IR-treated and non-IR-treated cells. Overexpression of TGM2 prevented, while knockdown of TGM2 aggravated the EMT inhibition caused by RSL3, indicating that RSL3 also sensitized glioma cells to IR by inhibiting EMT via a TGM2-dependent mechanism. Furthermore, in mice bearing human U87 tumor xenografts, RSL3 administration synergized with IR to inhibit tumor growth, accompanied by TGM2 inhibition, DNA DSBs, and EMT inhibition in tumor tissues. Taken together, we demonstrated that RSL3 sensitizes glioma cells to IR by suppressing TGM2-mediated DNA repair and EMT.

The Role of Transglutaminase 2 in Cancer: An Update

Transglutaminase type 2 (TG2) is the most ubiquitously expressed and well characterized member of the transglutaminase family. It is a ubiquitous multifunctional enzyme implicated in the regulation of several cellular pathways that support the survival, death, and general homeostasis of eukaryotic cells. Due to its multiple localizations both inside and outside the cell, TG2 participates in the regulation of many crucial intracellular signaling cascades in a tissue- and cell-specific manner, making this enzyme an important player in disease development and progression. Moreover, TG2 is capable of modulating the tumor microenvironment, a process of dynamic tissue remodeling and biomechanical events, resulting in changes which influence tumor initiation, growth, and metastasis. Even if generally related to the Ca2+-dependent post-translational modification of proteins, a number of different biological functions have been ascribed to TG2, like those of a peptide isomerase, protein kinase, guanine nucleotide binder, and cytosolic-nuclear translocator. With respect to cancer, TG2's role is controversial and highly debated; it has been described both as an anti- and pro-apoptotic factor and is linked to all the processes of tumorigenesis. However, numerous pieces of evidence support a tissue-specific role of TG2 so that it can assume both oncogenic and tumor-suppressive roles.