All-trans retinoic acid enhances temozolomide-induced autophagy in human glioma cells U251 via targeting Keap1/Nrf2/ARE signaling pathway

Abstract

The present study evaluated the retinoic acid (RA) enhancement of temozolomide (TMZ) effects on the human glioma cells U251 and explored its underlying molecular mechanism. The cell growth was detected using the MTT assay and the cell cycle was assessed by flow cytometry. Cell apoptosis was analyzed by Annexin V/propidium iodide staining, and the cell morphology was evaluated using transmission electron microscopy (TEM). Additionally, reverse transcription-PCR and western blot analysis were applied to detect the mRNA and protein levels. The RA treatment in combination with TMZ in the human U251 cells further inhibited cells growth, arresting cell cycle progression at the G0/G1 phase, and significantly induced apoptosis of U251 cells. After the RA+TMZ treatment of U251 cells, autophagy associated proteins Beclin 1 and LC3B were significantly increased, and the TEM analysis were consistent with autophagy protein levels. Moreover, Keap1/Nrf2/ARE expression was downregulated significantly, indicating the involvement in the mechanisms that RA treatment could enhance the TMZ effects on U251 cells. RA treatment in combination with TMZ may provide some experimental evidence for the possible effect of RA+TMZ against the growth and the proliferation of glioma cells. Therefore, the RA+TMZ administration may have potential utility for glioblastoma treatment.

A Potential Mechanism of Temozolomide Resistance in Glioma–Ferroptosis

“…Nrf2 and its downstream genes are highly expressed in many tumor cells (including gliomas) or tissues, and it has a role in promoting tumor growth, proliferation, and drug resistance (69)(70)(71)(72). Numerous studies have shown that Nrf2 also plays an important role in TMZ resistance in gliomas (73)(74)(75). The treatment of glioma cells with TMZ would induce high expression of Nrf2, and the inhibition of Nrf2 expression can increase the sensitivity of glioma cells to TMZ (73)(74)(75).…”

“…Numerous studies have shown that Nrf2 also plays an important role in TMZ resistance in gliomas (73)(74)(75). The treatment of glioma cells with TMZ would induce high expression of Nrf2, and the inhibition of Nrf2 expression can increase the sensitivity of glioma cells to TMZ (73)(74)(75).…”

The Multifaceted Role of CMA in Glioma: Enemy or Ally?

“…CMA involvement in TMZ’s mechanism of action has been also proposed by Shi et al [ 68 ], describing LAMP-2A stabilization after treatment with retinoic acid (RA). Indeed, in glioma, it has been shown that RA can support TMZ’s cytotoxic effect by improving autophagic induction and blocking cell proliferation in U251 glioma cells [ 68 ].…”

Retinol dehydrogenase 10 promotes metastasis of glioma cells via the transforming growth factor-β/SMAD signaling pathway

“…All-trans-retinoic acid has been used to treat glioma cells as it has been shown to significantly inhibit the proliferation of glioma cells and induce apoptosis. [23] Moreover, retinoic acid improves the pro-apoptosis effect of temozolomide on U251 cells via the Kelch-like ECH-associated protein 1-nuclear factor erythroid 2-related factor 2-antioxidant response elements signaling pathway, [24] which suggests that the retinoic acid signaling pathway possesses a strong inhibitory effect on proliferation of glioma at the cellular level. Recently, it has been shown that RDH10 is expressed in non-small cell lung cancer, mainly grade III disease, suggesting that it has a very important role in the development of this cancer.…”