Abstract:Background
Highly proliferating cancer cells exhibit the Warburg effect by regulation of PKM alternative splicing and promoting the expression of PKM2. Majority of the alternative splicing events are known to occur in the nuclear matrix where various MARBPs actively participate in the alternative splicing events. SMAR1, being a MARBP and an important tumor suppressor, is known to regulate the splicing of various cancer-associated genes. This study focuses on the regulation of PKM alternative sp… Show more
“…Cancer cells achieve the metabolic advantage over normal cells by modulating PKM alternative splicing and facilitating the PKM2 expression [ 19 ]. To further demonstrate whether RBX1 is responsible for this phenomenon, we detected the expression levels of RBX1, PKM2, and PKM1 in ATC patient samples and then compared these levels with those in the corresponding adjacent non-cancerous tissues using western blotting.…”
Section: Resultsmentioning
confidence: 99%
“…Previous studies have proven that UPS regulated the polyubiquitination and degradation of SMAR1 [ 19 ]. As the E3 ubiquitin ligase, RBX1, plays a role in protein degradation and recycling, we initially determined the degeneration of SMAR1 protein in RBX1-knockdown cells after inhibition of protein synthesis using cycloheximide (CHX).…”
Section: Resultsmentioning
confidence: 99%
“…The cloning of dual reporter PKM minigene system and dual reporter PKM minigene assay were performed as described previously [ 19 ]. Mean ± SD fold change in eGFP/mCherry ratio was calculated for each sample and compared with the control sample.…”
Section: Methodsmentioning
confidence: 99%
“…Therefore, targeting this alternative splicing step is shown to be an efficacious strategy for the elimination of cancer cells [ 17 , 18 ]. Recently, it has been shown that tumor suppressor SMAR1 regulates PKM alternative splicing by HDAC6-mediated deacetylation of PTBP1 [ 19 ]. Therefore, identification of the factors and mechanisms underlying PKM alternative splicing, resulting in the PKM2-mediated Warburg effect, is crucial for overcoming the current challenges in cancer treatment.…”
Background
Anaplastic thyroid carcinoma (ATC) is one of the most aggressive malignancies, frequently accompanied by metastasis and aerobic glycolysis. Cancer cells adjust their metabolism by modulating the PKM alternative splicing and facilitating PKM2 isoform expression. Therefore, identifying factors and mechanisms that control PKM alternative splicing is significant for overcoming the current challenges in ATC treatment.
Results
In this study, the expression of RBX1 was largely enhanced in the ATC tissues. Our clinical tests suggested that high RBX1 expression was significantly related to poor survival. The functional analysis indicated that RBX1 facilitated the metastasis of ATC cells by enhancing the Warburg effect, and PKM2 played a key role in RBX1-mediated aerobic glycolysis. Furthermore, we confirmed that RBX1 regulates PKM alternative splicing and promotes the PKM2-mediated Warburg effect in ATC cells. Moreover, ATC cell migration and aerobic glycolysis induced by RBX1-mediated PKM alternative splicing are dependent on the destruction of the SMAR1/HDAC6 complex. RBX1, as an E3 ubiquitin ligase, degrades SMAR1 in ATC through the ubiquitin–proteasome pathway.
Conclusion
Overall, our study identified the mechanism underlying the regulation of PKM alternative splicing in ATC cells for the first time and provides evidence about the effect of RBX1 on cellular adaptation to metabolic stress.
“…Cancer cells achieve the metabolic advantage over normal cells by modulating PKM alternative splicing and facilitating the PKM2 expression [ 19 ]. To further demonstrate whether RBX1 is responsible for this phenomenon, we detected the expression levels of RBX1, PKM2, and PKM1 in ATC patient samples and then compared these levels with those in the corresponding adjacent non-cancerous tissues using western blotting.…”
Section: Resultsmentioning
confidence: 99%
“…Previous studies have proven that UPS regulated the polyubiquitination and degradation of SMAR1 [ 19 ]. As the E3 ubiquitin ligase, RBX1, plays a role in protein degradation and recycling, we initially determined the degeneration of SMAR1 protein in RBX1-knockdown cells after inhibition of protein synthesis using cycloheximide (CHX).…”
Section: Resultsmentioning
confidence: 99%
“…The cloning of dual reporter PKM minigene system and dual reporter PKM minigene assay were performed as described previously [ 19 ]. Mean ± SD fold change in eGFP/mCherry ratio was calculated for each sample and compared with the control sample.…”
Section: Methodsmentioning
confidence: 99%
“…Therefore, targeting this alternative splicing step is shown to be an efficacious strategy for the elimination of cancer cells [ 17 , 18 ]. Recently, it has been shown that tumor suppressor SMAR1 regulates PKM alternative splicing by HDAC6-mediated deacetylation of PTBP1 [ 19 ]. Therefore, identification of the factors and mechanisms underlying PKM alternative splicing, resulting in the PKM2-mediated Warburg effect, is crucial for overcoming the current challenges in cancer treatment.…”
Background
Anaplastic thyroid carcinoma (ATC) is one of the most aggressive malignancies, frequently accompanied by metastasis and aerobic glycolysis. Cancer cells adjust their metabolism by modulating the PKM alternative splicing and facilitating PKM2 isoform expression. Therefore, identifying factors and mechanisms that control PKM alternative splicing is significant for overcoming the current challenges in ATC treatment.
Results
In this study, the expression of RBX1 was largely enhanced in the ATC tissues. Our clinical tests suggested that high RBX1 expression was significantly related to poor survival. The functional analysis indicated that RBX1 facilitated the metastasis of ATC cells by enhancing the Warburg effect, and PKM2 played a key role in RBX1-mediated aerobic glycolysis. Furthermore, we confirmed that RBX1 regulates PKM alternative splicing and promotes the PKM2-mediated Warburg effect in ATC cells. Moreover, ATC cell migration and aerobic glycolysis induced by RBX1-mediated PKM alternative splicing are dependent on the destruction of the SMAR1/HDAC6 complex. RBX1, as an E3 ubiquitin ligase, degrades SMAR1 in ATC through the ubiquitin–proteasome pathway.
Conclusion
Overall, our study identified the mechanism underlying the regulation of PKM alternative splicing in ATC cells for the first time and provides evidence about the effect of RBX1 on cellular adaptation to metabolic stress.
“…The last step is the conversion of phosphoenolpyruvate (PEP) into pyruvate and is performed by the pyruvate kinase enzyme, which has four isoforms including kinase muscle isoforms 1 and 2 (PKM1 and PKM2). PKM1 and PKM2 are the dominant isoforms of PKM that are found in most tissues [ 41 ]. The polypyrimidine tract-binding protein 1 (PTBP1) is important for splicing PKM into the PKM2 isoform over PKM1 [ 42 , 43 ].…”
Clinical studies indicate that patients infected with SARS-CoV-2 develop hyperinflammation, which correlates with increased mortality. The SARS-CoV-2/COVID-19-dependent inflammation is thought to occur via increased cytokine production and hyperactivity of RAGE in several cell types, a phenomenon observed for other disorders and diseases. Metabolic reprogramming has been shown to contribute to inflammation and is considered a hallmark of cancer, neurodegenerative diseases, and viral infections. Malfunctioning glycolysis, which normally aims to convert glucose into pyruvate, leads to the accumulation of advanced glycation end products (AGEs). Being aberrantly generated, AGEs then bind to their receptor, RAGE, and activate several pro-inflammatory genes, such as IL-1b and IL-6, thus, increasing hypoxia and inducing senescence. Using the lung epithelial cell (BEAS-2B) line, we demonstrated that SARS-CoV-2 proteins reprogram the cellular metabolism and increase pyruvate kinase muscle isoform 2 (PKM2). This deregulation promotes the accumulation of AGEs and senescence induction. We showed the ability of the PKM2 stabilizer, Tepp-46, to reverse the observed glycolysis changes/alterations and restore this essential metabolic process.
Several human diseases including viral infections activate the unfolded protein response (UPR) due to abnormal accumulation of unfolded/misfolded proteins. However, UPR modulation and its functional relevance in HIV‐1 infection lack comprehensive elucidation. This study reveals that HIV‐1 activates IRE1, PERK, and ATF6 signaling pathways of UPR. The knockdown of PERK and ATF6 reduces HIV‐1 long terminal repeat (LTR)‐driven gene expression, whereas the endoplasmic reticulum (ER) chaperone HSPA5 prevents proteasomal degradation of HIV‐1 p24 through its chaperone activity. Interestingly, overstimulation of UPR by a chemical inducer leads to anti‐HIV activity through an enhanced type‐1 interferon response. Also, treatment with a chemical ER stress inhibitor reduces HIV‐1 replication. These findings suggest that an optimal UPR activation is crucial for effective viral replication, as either overstimulating UPR or inhibiting ER stress leads to viral suppression.
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