The mitochondrial RNA polymerase POLRMT promotes skin squamous cell carcinoma cell growth

Identification of the central role of RNA polymerase mitochondrial for angiogenesis

Mitochondria are central to endothelial cell activation and angiogenesis, with the RNA polymerase mitochondrial (POLRMT) serving as a key protein in regulating mitochondrial transcription and oxidative phosphorylation. In our study, we examined the impact of POLRMT on angiogenesis and found that its silencing or knockout (KO) in human umbilical vein endothelial cells (HUVECs) and other endothelial cells resulted in robust anti-angiogenic effects, impeding cell proliferation, migration, and capillary tube formation. Depletion of POLRMT led to impaired mitochondrial function, characterized by mitochondrial depolarization, oxidative stress, lipid oxidation, DNA damage, and reduced ATP production, along with significant apoptosis activation. Conversely, overexpressing POLRMT promoted angiogenic activity in the endothelial cells. In vivo experiments demonstrated that endothelial knockdown of POLRMT, by intravitreous injection of endothelial specific POLRMT shRNA adeno-associated virus, inhibited retinal angiogenesis. In addition, inhibiting POLRMT with a first-in-class inhibitor IMT1 exerted significant anti-angiogenic impact in vitro and in vivo. Significantly elevated expression of POLRMT was observed in the retinal tissues of streptozotocin-induced diabetic retinopathy (DR) mice. POLRMT endothelial knockdown inhibited pathological retinal angiogenesis and mitigated retinal ganglion cell (RGC) degeneration in DR mice. At last, POLRMT expression exhibited a substantial increase in the retinal proliferative membrane tissues of human DR patients. These findings collectively establish the indispensable role of POLRMT in angiogenesis, both in vitro and in vivo.

Mitochondria transcription and cancer

Mitochondria are major organelles involved in several processes related to energy supply, metabolism, and cell proliferation. The mitochondria function is transcriptionally regulated by mitochondria DNA (mtDNA), which encodes the key proteins in the electron transport chain that is indispensable for oxidative phosphorylation (OXPHOS). Mitochondrial transcriptional abnormalities are closely related to a variety of human diseases, such as cardiovascular diseases, and diabetes. The mitochondria transcription is regulated by the mtDNA, mitochondrial RNA polymerase (POLRMT), two transcription factors (TFAM and TF2BM), one transcription elongation (TEFM), and one known transcription termination factor (mTERFs). Dysregulation of these factors directly leads to altered expression of mtDNA in tumor cells, resulting in cellular metabolic reprogramming and mitochondrial dysfunction. This dysregulation plays a role in modulating tumor progression. Therefore, understanding the role of mitochondrial transcription in cancer can have implications for cancer diagnosis, prognosis, and treatment. Targeting mitochondrial transcription or related pathways may provide potential therapeutic strategies for cancer treatment. Additionally, assessing mitochondrial transcriptional profiles or biomarkers in cancer cells or patient samples may offer diagnostic or prognostic information.

Integrated analysis of lactate-related genes identifies POLRMT as a novel marker promoting the proliferation, migration and energy metabolism of hepatocellular carcinoma via Wnt/β-Catenin signaling

Hepatocellular carcinoma (HCC) is a prevalent and deadly form of cancer globally with typically unfavorable outcomes. Increasing research suggests that lactate serves as an important carbon contributor to cellular metabolism and holds a crucial part in the progression, sustenance, and treatment response of tumors. However, the contribution of lactate-related genes (LRGs) in HCC is still unclear. In this study, we analyzed TCGA datasets and screened 21 differentially expressed LRGs related to long-term survivals in HCC patients. Pan-cancer assays revealed that 21 LRGs expression exhibited a dysregulated level in man types of tumors and associated with clinical prognosis of tumor patients. The analysis of 21 LRGs successfully classified HCC samples into two molecular subtypes, and these two subtypes showed significant differences in clinical information, gene expression, and immune characteristics. Subsequently, based on the aforementioned 21 LRGs, a novel prognostic signature (DTYMK, IRAK1, POLRMT, MPV17, UQCRH, PDSS1, SLC16A3, SPP1 and LDHD) was generated by LASSO-Cox regression analysis. Survival assays demonstrated that the signature performed well in predicting the overall survival of patients with HCC. The results of Gene Set Variation Analysis indicated that the high GSVA scores were associated with poor prognosis. Moreover, we also investigated the correlation between GSVA scores and various signaling pathways in HCC. Among the nine prognostic genes, our attention focused on POLRMT which was highly expressed in HCC specimens based on TCGA datasets and several HCC cell lines. In addition, functional assays indicated that POLRMT distinctly promoted the proliferation, migration and energy metabolism of HCC cells via regulating Wnt/β-Catenin signaling. Overall, through the establishment of a novel prognostic signature, we have provided potential clinical value for assessing the prognosis of HCC patients. Furthermore, our study has identified the high expression of POLRMT in HCC and demonstrated its crucial role in HCC cell proliferation. These findings hold great importance in advancing our understanding of the pathophysiology of HCC, identifying new therapeutic targets, and improving patient survival rates.

Targeting POLRMT by a first-in-class inhibitor IMT1 inhibits osteosarcoma cell growth in vitro and in vivo

Osteosarcoma (OS) is a highly aggressive form of bone cancer that predominantly affects adolescents and young adults. In this study, we have undertaken an investigation into the potential anti-OS cell activity of IMT1 (inhibitor of mitochondrial transcription 1), a first-in-class inhibitor of RNA polymerase mitochondrial (POLRMT). IMT1 exhibited a profound inhibitory effect on cell survival, proliferation, cell cycle progression, and migration in primary and immortalized OS cells. Furthermore, this POLRMT inhibitor elicited apoptosis in the OS cells, without, however, inducing cytotoxicity in human osteoblasts or osteoblastic cells. IMT1 disrupted mitochondrial functions in OS cells, resulting in mitochondrial depolarization, oxidative injury, lipid peroxidation, and ATP reduction in OS cells. Silencing POLRMT using targeted shRNA closely mimicked the actions of IMT1 and exerted potent anti-OS cell activity. Importantly, IMT1's effectiveness was diminished in POLRMT-silenced OS cells. Subsequent investigations revealed that IMT1 suppressed the activation of the Akt-mammalian target of rapamycin (mTOR) cascade in OS cells. IMT1 treatment or POLRMT silencing in primary OS cells led to a significant reduction in Akt1-S6K-S6 phosphorylation. Conversely, it was enhanced upon POLRMT overexpression. The restoration of Akt-mTOR activation through the introduction of a constitutively active S473D mutant Akt1 (caAkt1) mitigated IMT1-induced cytotoxicity in OS cells. In vivo, oral administration of IMT1 robustly curtailed the growth of OS xenografts in nude mice. Furthermore, IMT1 suppressed POLRMT activity, impaired mitochondrial function, repressed Akt-mTOR activation, and induced apoptosis within xenograft tissues. Collectively, these findings underscore the potent growth-inhibitory effects attributed to IMT1 via targeted POLRMT inhibition. The utilization of this POLRMT inhibitor carries substantial therapeutic promise in the context of OS treatment.

Identification of the mitochondrial protein POLRMT as a potential therapeutic target of prostate cancer

RNA polymerase mitochondria (POLRMT) is essential for mitochondrial transcription machinery and other mitochondrial functions. Its expression and potential functions in prostate cancer were explored here. The Cancer Genome Atlas prostate cancer cohort (TCGA PRAD) shows that POLRMT mRNA expression is upregulated in prostate cancer tissues and POLRMT upregulation is correlated with poor patients' survival. POLRMT mRNA and protein levels were upregulated in local prostate cancer tissues and different primary/immortalized prostate cancer cells. Genetic depletion of POLRMT, using viral shRNA or CRISPR/Cas9 gene editing methods, impaired mitochondrial functions in prostate cancer cells, leading to mitochondrial depolarization, oxidative stress, mitochondria complex I inhibition, and ATP depletion. Moreover, POLRMT depletion resulted in robust inhibition of prostate cancer cell viability, proliferation, and migration, and provoked apoptosis. Conversely, prostate cancer cell proliferation, migration, and ATP contents were strengthened following ectopic POLRMT overexpression. In vivo, intratumoral injection of POLRMT shRNA adeno-associated virus impeded prostate cancer xenograft growth in nude mice. POLRMT silencing, oxidative stress, and ATP depletion were detected in POLRMT shRNA-treated prostate cancer xenograft tissues. IMT1 (inhibitor of mitochondrial transcription 1), the first-in-class POLRMT inhibitor, inhibited prostate cancer cell growth in vitro and in vivo. Together, overexpressed POLRMT is an important mitochondrial protein for prostate cancer cell growth, representing a novel and promising diagnostic and therapeutic oncotarget.

POLRMT over-expression is linked to WNT/beta-catenin signaling, immune infiltration, and unfavorable outcomes in lung adenocarcinoma patients

BACKGROUND

Mitochondrial RNA polymerase (POLRMT) is essential for the expression of mitochondrial genes. In recent studies, POLRMT expression promoted non-small cell cancer cell proliferation in cell lines and xenografts. The present study investigated the impact of POLRMT expression and function on lung adenocarcinoma (LUAD) patients.

METHOD

Multi-omics data (genomics, transcriptomics, and proteomics) from publicly available databases were used to assess the role of POLRMT expression and function in LUAD. These findings were further verified using cancer tissues from clinical samples.

RESULTS

POLRMT was over-expressed in LUADs, with mutation frequencies ranging from 1.30% to 5.71%. Over-expression of POLRMT was associated with an abnormal clinicopathological condition resulting in a decreased lifespan. Furthermore, gene sets enrich analysis revealed that POLRMT expression was linked to WNT/beta-catenin signaling; the expression of downstream target genes was positively correlated with POLRMT expression. Also, POLRMT expression was positively correlated with immunosuppressive genes, thereby affecting immune infiltration.

CONCLUSION

POLRMT is over-expressed in LUAD, thereby impacting patient survival. It is also involved in WNT/beta-catenin signaling and may affect tumor infiltration.

Targeting Mitochondrial DNA Transcription by POLRMT Inhibition or Depletion as a Potential Strategy for Cancer Treatment

Transcription of the mitochondrial genome is essential for the maintenance of oxidative phosphorylation (OXPHOS) and other functions directly related to this unique genome. Considerable evidence suggests that mitochondrial transcription is dysregulated in cancer and cancer metastasis and contributes significantly to cancer cell metabolism. Recently, inhibitors of the mitochondrial DNA-dependent RNA polymerase (POLRMT) were identified as potentially attractive new anti-cancer compounds. These molecules (IMT1, IMT1B) inactivate cancer cell metabolism through reduced transcription of mitochondrially-encoded OXPHOS subunits such as ND1-5 (Complex I) and COI-IV (Complex IV). Studies from our lab have discovered small molecule regulators of the mitochondrial matrix caseinolytic protease (ClpP) as probable inhibitors of mitochondrial transcription. These compounds activate ClpP proteolysis and lead to the rapid depletion of POLRMT and other matrix proteins, resulting in inhibition of mitochondrial transcription and growth arrest. Herein we present a comparison of POLRMT inhibition and ClpP activation, both conceptually and experimentally, and evaluate the results of these treatments on mitochondrial transcription, inhibition of OXPHOS, and ultimately cancer cell growth. We discuss the potential for targeting mitochondrial transcription as a cancer cell vulnerability.

A first-in-class POLRMT specific inhibitor IMT1 suppresses endometrial carcinoma cell growth

Exploring novel molecularly-targeted therapies for endometrial carcinoma is important. The current study explored the potential anti-endometrial carcinoma activity by a first-in-class POLRMT (RNA polymerase mitochondrial) inhibitor IMT1. In patient-derived primary human endometrial carcinoma cells and established lines, treatment with IMT1 potently inhibited cell viability, proliferation, cell-cycle progression and motility, while inducing robust caspase-apoptosis activation. Treatment with the PLORMT inhibitor impaired mitochondrial functions, leading to mtDNA (mitochondrial DNA) transcription inhibition, mitochondrial membrane potential decline, reactive oxygen species formation, oxidative stress and ATP loss in the endometrial carcinoma cells. Similarly, POLRMT depletion, through shRNA-induced silencing or CRISPR/Cas9-caused knockout (KO), inhibited primary endometrial carcinoma cell proliferation and motility, and induced mitochondrial dysfunction and apoptosis. Importantly, IMT1 failed to induce further cytotoxicity in POLRMT-KO endometrial carcinoma cells. Contrarily, ectopic overexpression of POLRMT further augmented proliferation and motility of primary endometrial carcinoma cells. In vivo, oral administration of a single dose of IMT1 substantially inhibited endometrial carcinoma xenograft growth in the nude mice. mtDNA transcription inhibition, oxidative stress, ATP loss and apoptosis were detected in IMT1-treated endometrial carcinoma xenograft tissues. Together, targeting PLORMT by IMT1 inhibited endometrial carcinoma cell growth in vitro and in vivo.