Accumulation of the SET protein in HEK293T cells and mild oxidative stress: cell survival or death signaling

Abstract

SET protein (I2PP2A) is an inhibitor of PP2A, which regulates the phosphorylated Akt (protein kinase B) levels. We assessed the effects of SET overexpression in HEK293T cells, both in the presence and the absence of mild oxidative stress induced by 50 μM tert-butyl hydroperoxide. Immunoblotting assays demonstrated that SET accumulated in HEK293T cells and increased the levels of phosphorylated Akt and PTEN; in addition, SET decreased glutathione antioxidant defense of cell and increased expression of genes encoding antioxidant defense proteins. Immunofluorescence analysis demonstrated that accumulated SET was equally distributed in cytoplasm and nucleus; however, in cells that had been exposed to oxidative stress, SET was found in large aggregates in the cytoplasm. SET accumulation in HEK293T cells correlated with inhibition of basal apoptosis as evidenced by a decrease in annexin V staining and activity of caspases; under mild oxidative stress, SET accumulation correlated with caspase-independent cell death, as evidenced by increased PI and annexin V/PI double staining. The results suggest that accumulated SET could act via Akt/PTEN either as cell survival signal or as oxidative stress sensor for cell death.

Stable SET knockdown in head and neck squamous cell carcinoma promotes cell invasion and the mesenchymal-like phenotype in vitro, as well as necrosis, cisplatin sensitivity and lymph node metastasis in xenograft tumor models

“…Five-μm sections were stained with H&E for histological analysis. Three-μm sections were used for the immunohistochemical analysis of SET, Ki67, pan-CTKR, p62, pERK1/2, and p-p53 Ser15 proteins as previously described [5]. The following primary antibodies were used: Ki67 (ab15580; Abcam, Cambridge, England), p62/SQSTM1 (D-3: sc-28359; Santa Cruz Biotechnologies, Santa Cruz, CA, USA), pan-CTKR, SET, pERK1/2 and p-p53 Ser15 .…”

“…SET-mediated PP2A inhibition occurs via dephosphorylation of proteins, such as the extracellular signal-regulated kinase (ERK) [3] and protein kinase B (Akt) [4]. Recently, we demonstrated that SET accumulates in head and neck squamous cell carcinoma (HNSCC) and suggested a new role for SET as a sensor of oxidative stress, thereby promoting cell survival in association with increased phosphorylated Akt levels and an enhanced antioxidant defense [5]. …”

Deregulation of the PP2A Inhibitor SET Shows Promising Therapeutic Implications and Determines Poor Clinical Outcome in Patients with Metastatic Colorectal Cancer

“…Of importance, SET plays an oncogenic role modulating signaling pathways with high relevance in human cancer (11). For instance, it has been reported that SET activates the transcription factor AP-1, deregulates AKT signaling, inhibits the DNase activity of the tumor-suppressor NM23-H1, or negatively regulates p53 acetylation, thus repressing its activity (12)(13)(14)(15)(16). Moreover, SET is overexpressed in several neoplasms (17)(18)(19)(20)(21) and it has been proposed as a novel molecular target for anticancer therapy (20)(21)(22)(23).…”

Expression of set is downregulated by rapamycin in human colorectal cancer cells

“…Almeida et al (16) assessed the effect of the overexpression of the SET protein, a histone acetylation modulator accumulated in head and neck squamous cell carcinoma, on the gene regulation and protein activity of aldehyde dehydrogenase 2 and glutathione S-transferase P1. Leopoldino et al (17) reported that accumulated set may act via the Akt̸PTEN pathway as a cell survival signal or as an oxidative stress sensor promoting cell death. The studies mentioned above indicated that set may be involved in the development of several malignant tumors.…”