Prolyl Hydroxylase 3 Knockdown Accelerates VHL-Mutant Kidney Cancer Growth In Vivo

PHD3 inhibits colon cancer cell metastasis through the occludin-p38 pathway

Prolyl hydroxylase 3 (PHD3) hydroxylates HIFα in the presence of oxygen, leading to HIFα degradation. PHD3 inhibits tumorigenesis. However, the underlying mechanism is not well understood. Herein, we demonstrate that PHD3 inhibits the metastasis of colon cancer cells through the occludin-p38 MAPK pathway independent of its hydroxylase activity. We find that PHD3 inhibits colon cancer cell metastasis in the presence of the PHD inhibitor DMOG, and prolyl hydroxylase-deficient PHD3(H196A) suppresses cell metastasis as well. PHD3 controls the stability of the tight junction protein occludin in a hydroxylase-independent manner. We further find that PHD3-inhibited colon cancer cell metastasis is rescued by knockdown of occludin and that occludin acts as a negative regulator of cell metastasis, implying that PHD3 suppresses metastasis through occludin. Furthermore, knockdown of occludin induces phosphorylation of p38 MAPK, and the p38 inhibitor SB203580 impedes cell migration and invasion induced by occludin knockdown, indicating that occludin functions through p38. Moreover, knockdown of occludin enhances the expression of MKK3/6, the upstream kinase of p38, while overexpression of occludin decreases its expression. Our results suggest that PHD3 inhibits the metastasis of colon cancer cells through the occludin-p38 pathway independent of its hydroxylase activity. These findings reveal a previously undiscovered mechanism underlying the regulation of cancer cell metastasis by PHD3 and highlight a noncanonical hydroxylase-independent function of PHD3 in the suppression of cancer cells.

Integrated analysis of the roles of oxidative stress related genes and prognostic value in clear cell renal cell carcinoma

BACKGROUND

Patients with clear cell renal cell carcinoma (ccRCC), which is the most commonly diagnosed subtype of renal cell carcinoma, are at risk of tumor metastasis and recrudescence. Previous research has shown that oxidative stress can induce tumorigenesis in many cancers and can be a target of cancer treatment. Despite these findings, little progress has been made understanding in the association of oxidative stress-related genes (OSRGs) with ccRCC.

METHODS

In vitro experiments were conducted with MTT survival assays, qRT‒PCR, apoptosis assays, cell cycle assays, ROS assays, and IHC staining.

RESULTS

In our study, 12 differentially expressed oxidative stress-related genes (DEOSGs) and related transcription factors (TFs) that are relevant to overall survival (OS) were screened, and their mutual regulatory networks were constructed with data from the TCGA database. Moreover, we constructed a risk model of these OSRGs and performed clinical prognostic analysis and validation. Next, we performed protein-protein interaction (PPI) network analysis and Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analysis of MELK, PYCR1, and PML. A tissue microarray also verified the high expression of MELK and PYCR1 in ccRCC. Finally, in vitro cellular experiments demonstrated that knockdown of MELK or PYCR1 significantly inhibited ccRCC cell proliferation by causing cell apoptosis and inducing cell cycle arrest in the G1 phase. Intracellular ROS levels were elevated after these two genes were knocked down.

CONCLUSION

Our results revealed the potential DEORGs to be used in ccRCC prognostic prediction and identified two biomarkers, named PYCR1 and MELK, which regulated the proliferation of ccRCC cells by affecting ROS levels. Furthermore, PYCR1 and MELK could be promising targets for predicting the progression and prognosis of ccRCC, thereby serving as new targets for medical treatments.

The multifaceted role of EGLN family prolyl hydroxylases in cancer: going beyond HIF regulation

EGLN1, EGLN2 and EGLN3 are proline hydroxylase whose main function is the regulation of the HIF factors. They work as oxygen sensors and are the main responsible of HIFα subunits degradation in normoxia. Being their activity strictly oxygen-dependent, when oxygen tension lowers, their control on HIFα is released, leading to activation of systemic and cellular response to hypoxia. However, EGLN family members activity is not limited to HIF modulation, but it includes the regulation of essential mechanisms for cell survival, cell cycle metabolism, proliferation and transcription. This is due to their reported hydroxylase activity on a number of non-HIF targets and sometimes to hydroxylase-independent functions. For these reasons, EGLN enzymes appear fundamental for development and progression of different cancer types, playing either a tumor-suppressive or a tumor-promoting role, according to EGLN isoform and to tumor context. Notably, EGLN1, the most studied isoform, has been shown to have also a central role in tumor micro-environment modulation, mediating CAF activation and impairing HIF1α -related angiogenesis, thus covering an important function in cancer metastasis promotion. Considering the recent knowledge acquired on EGLNs, the possibility to target these enzymes for cancer treatment is emerging. However, due to their multifaceted and controversial roles in different cancer types, the use of EGLN inhibitors as anti-cancer drugs should be carefully evaluated in each context.

Neurogenic and pericytic plasticity of conditionally immortalized cells derived from renal erythropoietin-producing cells

In adult mammals, the kidney is the main source of circulating erythropoietin (Epo), the master regulator of erythropoiesis. In vivo data in mice demonstrated multiple subtypes of interstitial renal Epo‐producing (REP) cells. To analyze the differentiation plasticity of fibroblastoid REP cells, we used a transgenic REP cell reporter mouse model to generate conditionally immortalized REP‐derived (REPD) cell lines. Under nonpermissive conditions, REPD cells ceased from proliferation and acquired a stem cell‐like state, with strongly enhanced hypoxia‐inducible factor 2 (HIF‐2α), stem cell antigen 1 (SCA‐1), and CD133 expression, but also enhanced alpha‐smooth muscle actin (αSMA) expression, indicating myofibroblastic signaling. These cells maintained the “on‐off” nature of Epo expression observed in REP cells in vivo, whereas other HIF target genes showed a more permanent regulation. Like REP cells in vivo, REPD cells cultured in vitro generated long tunneling nanotubes (TNTs) that aligned with endothelial vascular structures, were densely packed with mitochondria and became more numerous under hypoxic conditions. Although inhibition of mitochondrial oxygen consumption blunted HIF signaling, removal of the TNTs did not affect or even enhance the expression of HIF target genes. Apart from pericytes, REPD cells readily differentiated into neuroglia but not adipogenic, chondrogenic, or osteogenic lineages, consistent with a neuronal origin of at least a subpopulation of REP cells. In summary, these results suggest an unprecedented combination of differentiation features of this unique cell type.