Chronic Inhibition of STAT3/STAT5 in Treatment-Resistant Human Breast Cancer Cell Subtypes: Convergence on the ROS/SUMO Pathway and Its Effects on xCT Expression and System xc- Activity

Abstract

Pharmacologically targeting activated STAT3 and/or STAT5 has been an active area of cancer research. The cystine/glutamate antiporter, system xc-, contributes to redox balance and export of intracellularly produced glutamate in response to up-regulated glutaminolysis in cancer cells. We have previously shown that blocking STAT3/5 using the small molecule inhibitor, SH-4-54, which targets the SH2 domains of both proteins, increases xCT expression, thereby increasing system xc- activity in human breast cancer cells. The current investigation demonstrates that chronic SH-4-54 administration, followed by clonal selection of treatment-resistant MDA-MB-231 and T47D breast cancer cells, elicits distinct subtype-dependent effects. xCT mRNA and protein levels, glutamate release, and cystine uptake are decreased relative to untreated passage-matched controls in triple-negative MDA-MB-231 cells, with the inverse occurring in estrogen-responsive T47D cells. This “ying-yang” effect is linked with a shifted balance between the phosphorylation status of STAT3 and STAT5, intracellular ROS levels, and STAT5 SUMOylation/de-SUMOylation. STAT5 emerged as a definitive negative regulator of xCT at the transcriptional level, while STAT3 activation is coupled with increased system xc- activity. We propose that careful classification of a patient’s breast cancer subtype is central to effectively targeting STAT3/5 as a therapeutic means of treating breast cancer, particularly given that xCT is emerging as an important biomarker of aggressive cancers.

Epilepsy Associates with Decreased HIF-1α/STAT5b Signaling in Glioblastoma

“…High expression of connexin 43 has in turn been linked to both glioma-related [46] and epilepsy due to mesiotemporal sclerosis [47], while this latter presents reduced levels of connexin 32. On the other hand, STAT5 is a negative regulator of xCT Expression and System Xc-Activity [48]. The exploration of these potential correlations is beyond the scope of the present work but represents an interesting venue for future research.…”

Functional effects of TrkA inhibition on system xC−-mediated glutamate release and cancer-induced bone pain

“…Interestingly, serine kinases, including MAPK, phosphorylate signal transducer and activator of transcription 3 (STAT3), which then homo- or heterodimerizes and translocates into the nucleus. 35 , 51 , 52 where it then binds specific DNA recognition elements to regulate expression of genes, including xCT. 51 In MDA-MB-231 breast cancer cells, for example, the MAPK inhibitor PD098059 abolishes basal xCT transcriptional activity.…”

“…mRNA was quantified using qualitative real-time polymerase chain reaction (qPCR) as previously described. 35 Briefly, 10 6 4T1 cells were seeded in 10 cm dishes and treated with 100 ng β-NGF in the presence (6 µM) or absence (DMSO) of the TrkA inhibitor AG879 for 24 h. Total RNA isolation from cell pellets was conducted using the Qiagen RNeasy kit (Qiagen Inc.). cDNA was then synthesized via reverse transcription using Superscript III and oligo DTs (Thermo Fisher Scientific), and qPCR assays were performed in duplicate using xCT primers (detailed in Table 1 ) and SsoAdvanced Universal SYBR Green Supermix (BioRad).…”

Amino Acid Transporters and Glutamine Metabolism in Breast Cancer

“…Nuclear factor erythroid 2-related factor 2 [ 58 ] and insulin-like growth factor-1 [ 59 ] are positive regulators that upregulate SLC7A11 expression. In contrast, signal transducer and activator of transcription (STAT) 3/STAT5 [ 60 , 61 ] and miR-26b [ 62 ] are negative regulators that inhibit SLC7A11 expression in breast cancer.…”