Structural and Functional Diversity of the Peroxiredoxin 6 Enzyme Family

PRDX6 knockdown sensitizes multiple myeloma cells to ferroptosis through inactivation of the PI3K/AKT pathway

BACKGROUND

This study probes into the impact and mechanisms of PRDX6 on ferroptosis multiple myeloma (MM).

RESEARCH DESIGN AND METHODS

PRDX6 expression in MM cells were determined using Western blotting and qRT-PCR. MM cells were treated with pLKO-shPRDX6 vectors expressing PRDX6 shRNA alone or in combination with Erastin/ferrostatin-1 (ferroptosis activator/inhibitor) or 740Y-P (PI3K/AKT pathway activator). Cell viability, apoptosis, Fe2+ concentration, and ROS levels were examined using CCK-8, flow cytometric analysis, iron ion detection, and DCFH-DA assay, and ELISA. Malondialdehyde (MDA) and glutathione (GSH) levels were tested with ELISA, and SLC7A11 and GPX4 levels were measured with Western blotting.

RESULTS

PRDX6 expression was sharply increased in MM cells (p < 0.01). Silencing of PRDX6 sensitized MM cells to ferroptosis, as indicated by elevated Fe2+, ROS, and MDA levels but decreased GSH, SLC7A11, and GPX4 levels (p < 0.05), and these trends were neutralized by 740Y-P treatment. Furthermore, PRDX6 knockdown lowered the levels of PI3K/AKT pathway-associated molecules (p < 0.05).

CONCLUSIONS

PRDX6 knockdown may exert pro-ferroptotic effects through inactivation of the PI3K/AKT pathway, underlying an appealing therapeutic target for MM.

Role of aspartate 42 and histidine 79 in the aiPLA2 activity and oligomeric status of Prdx6 at low pH

Peroxiredoxin 6 (Prdx6), a unique non-seleno peroxidase, is a bifunctional protein with GSH peroxidase at pH 7.4 and calcium independent phospholipase A2 (aiPLA2) activities at pH 4.0. Changes in pH brings about alteration in the conformational and thermodynamic stability of Prdx6. For instance, under acidic condition (pH 4.0), Prdx6 forms higher oligomers with concommittant gain in aiPLA2 activity that is resistant to thermal denaturation. However, there has been no molecular level understanding of how low pH induces formation of oligomers. In the present study, site directed mutagenesis of two conserved amino acid residues, Asp42 and His79, was used to study the molecular basis for the influence of pH on the oligomeric state of Prdx6. We observed that mutation at Asp42 and His79 residues by Ala did not result in a significant change in its peroxidase activity at neutral pH 7.4, but its aiPLA2 activity at low pH 4.0 decreased significantly. At this pH condition, both mutants exhibit highly conserved alpha-helix content but fluctuating tryptophan micro-environment with partly exposed hydrophobic patches that render the formation of oligomers. DLS measurements and analytical SEC revealed that Wt Prdx6 forms oligomers at low pH but not the mutant proteins suggesting the importance of these residues in pH sensing and oligomerization. These results suggest that Asp42 and His79 interact each other to induce conformational change of Prdx6 that triggers the oligomerization of Prdx6 at low pH.

PRDX6 Prevents NNMT Ubiquitination and Degradation as a Nonenzymatic Mechanism to Promote Ovarian Cancer Progression

Cancer cells cope with oxidative stress for their proliferation and metastasis by equipping antioxidant systems, among which the antioxidant enzymes peroxiredoxins (PRDXs) play crucial roles. However, whether PRDXs exhibit nonenzymatic functions remains unclear. Here, it is shown that the 1-cysteine PRDX (PRDX6) upregulates nicotinamide N-methyltransferase (NNMT) to promote the growth and metastasis of ovarian cancer cells, independently of PRDX6's enzymatic activities. Mechanistically, PRDX6 interacts with NNMT to prevent its binding to the E3 ubiquitin ligase tripartite-motif protein 56 (TRIM56), leading to the inhibition of NNMT ubiquitination at lysine 23 and 210 and suppression of subsequent proteasomal degradation. In addition, PRDX6-mediated NNMT upregulation activates mitogen-activated protein kinase (MAPK) signaling, thereby promoting the growth and metastasis of ovarian cancer cells. Notably, PRDX6 overexpression is associated with higher NNMT protein levels in human ovarian cancer tissues and is predictive of poor prognosis of ovarian cancer patients. Overall, the findings illustrate a critical oncogenic mechanism of the antioxidant enzyme PRDX6 in promoting ovarian cancer progression beyond its enzymatic mechanisms.

Unveiling the Significance of Peroxiredoxin 6 in Central Nervous System Disorders

Peroxiredoxin 6 (Prdx6), a unique 1-Cys member of the peroxiredoxin family, exhibits peroxidase activity, phospholipase activity, and lysophosphatidylcholine acyltransferase (LPCAT) activity. Prdx6 has been known to be an important enzyme for the maintenance of lipid peroxidation repair, cellular metabolism, inflammatory signaling, and antioxidant damage. Growing research has demonstrated that the altered activity of this enzyme is linked with various pathological processes including central nervous system (CNS) disorders. This review discusses the distinctive structure, enzyme activity, and function of Prdx6 in different CNS disorders, as well as emphasizing the significance of Prdx6 in neurological disorders.