Overexpression of PSAT1 regulated by G9A sustains cell proliferation in colorectal cancer.
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ABSTRACT:
SUBMITTER: Wang H
PROVIDER: S-EPMC7162942 | biostudies-literature |
REPOSITORIES: biostudies-literature
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Project description:Research into the metabolism of the non-essential amino acid (NEAA) proline in cancer has gained traction in recent years. The last step in the proline biosynthesis pathway is catalyzed by pyrroline-5-carboxylate reductase (PYCR) enzymes. There are three PYCR enzymes: mitochondrial PYCR1 and 2 and cytosolic PYCR3 encoded by separate genes. The expression of the PYCR1 gene is increased in numerous malignancies and correlates with poor prognosis. PYCR1 expression sustains cancer cells' proliferation and survival and several mechanisms have been implicated to explain its oncogenic role. It has been suggested that the biosynthesis of proline is key to sustain protein synthesis, support mitochondrial function and nucleotide biosynthesis. However, the links between proline metabolism and cancer remain ill-defined and are likely to be tissue specific. Here we use a combination of human dataset, human tissue and mouse models to show that the expression levels of the proline biosynthesis enzymes are significantly increased during colorectal tumorigenesis. Functionally, the expression of mitochondrial PYCRs is necessary for cancer cells' survival and proliferation. However, the phenotypic consequences of PYCRs depletion could not be rescued by external supplementation with either proline or nucleotides. Overall, our data suggest that, despite the mechanisms underlying the role of proline metabolism in colorectal tumorigenesis remain elusive, targeting the proline biosynthesis pathway is a suitable approach for the development of novel anti-cancer therapies.
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Project description:G9a is the major mammalian H3-K9 methyltransferase that targets euchromatic regionsand is essential for murine embryogenesis . We demonstrate that G9a is endowed with methyltransferase activity to concomitantly repress the downstream effector Ep-CAM, thereby promoting the invasion step of the invasion-metastasis cascade. We used microarrays to detail the G9a regulated gene expression underlying invasion-metastasis cascade and identified distinct classes of up-regulated genes during this process. Lung adenocarcinoma cells with G9a knockdown or overexpression were selected for RNA extraction and hybridization on Affymetrix microarrays.
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Project description:BackgroundA growing amount of evidence has indicated that PSAT1 is an oncogene that plays an important role in cancer progression and metastasis. In this study, we explored the expression and function of PSAT1 in estrogen receptor (ER)-negative breast cancer.MethodThe expression level of PSAT1 in breast cancer tissues and cells was analyzed using real-time-PCR (RT-PCR), TCGA datasets or immunohistochemistry (IHC). The overall survival of patients with ER-negative breast cancer stratified by the PSAT1 expression levels was evaluated using Kaplan-Meier analysis. The function of PSAT1 was analyzed using a series of in vitro assays. Moreover, a nude mouse model was used to evaluate the function of PSAT1 in vivo. qRT-PCR and western blot assays were used to evaluate gene and protein expression, respectively, in the indicated cells. In addition, we demonstrated that PSAT1 was activated by ATF4 by chromatin immunoprecipitation (ChIP) assays.ResultsmRNA expression of PSAT1 was up-regulated in ER-negative breast cancer. A tissue microarray that included 297 specimens of ER-negative breast cancer was subjected to an immunohistochemistry assay, which demonstrated that PSAT1 was overexpressed and predicted a poor clinical outcome of patients with this disease. Our data showed that PSAT1 promoted cell proliferation and tumorigenesis in vitro and in vivo. We further found that PSAT1 induced up-regulation of cyclin D1 via the GSK3β/β-catenin pathway, which eventually led to the acceleration of cell cycle progression. Furthermore, ATF4 was also overexpressed in ER-negative breast cancers, and a positive correlation between the ATF4 and PSAT1 mRNA levels was observed in ER-negative breast cancers. We further demonstrated that knockdown of ATF4 by siRNA reduced PSAT1 expression. Finally, chromatin immunoprecipitation (ChIP) assays showed that PSAT1 was a target of ATF4.ConclusionsPSAT1, which is overexpressed in ER-negative breast cancers, is activated by ATF4 and promotes cell cycle progression via regulation of the GSK3β/β-catenin/cyclin D1 pathway.
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Project description:G9a, a histone methyltransferase, is aberrantly expressed in some human tumor types. By comparing 182 paired colorectal cancer and peritumoral tissues, we found that G9a was highly expressed in colorectal cancer (CRC). Overexpression of G9a promoted CRC cells proliferation and colony formation, whereas knockdown of G9a inhibited CRC cells proliferation. Depletion of G9a increased the rate of chromosome aberration, induced DNA double strand breaks and CRC cells senescence. G9a inhibition synergistically increased γH2AX expression induced by topoisomerase I inhibitors and ultimately led to CRC cell death. The findings that down-regulation of G9a triggers DNA damage response and inhibits colorectal cancer cells proliferation may define G9a as potential oncotarget in CRC.
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