Maturation of Mitochondrially Targeted Prx V Involves a Second Cleavage by Mitochondrial Intermediate Peptidase That Is Sensitive to Inhibition by H2O2

Human mitochondrial peroxiredoxin Prdx3 is dually localized in the intermembrane space and matrix subcompartments

Peroxiredoxin 3 (Prdx3) is the major sink for H2O2 and other hydroperoxides within mitochondria, yet the mechanisms guiding the import of its cytosolic precursor into mitochondrial sub-compartments remain elusive. Prdx3 is synthesized in the cytosol as a precursor with an N-terminal cleavable presequence, which is frequently proposed to target the protein exclusively to the mitochondrial matrix. Here, we present a comprehensive analysis of the human Prdx3 biogenesis, using highly purified mitochondria from HEK293T cells. Subfractionation and probing for specific mitochondrial markers confirmed Prdx3 localization in the matrix, while unexpectedly revealed its presence in the mitochondrial intermembrane space (IMS). Both matrix and IMS isoforms were found to be soluble proteins, as demonstrated by alkaline carbonate extraction. By combining in silico analysis, in organello import assays and heterologous expression in yeast, we found that Prdx3 undergoes sequential proteolytic processing steps by mitochondrial processing peptidase (MPP) and mitochondrial intermediate peptidase (MIP) during its import into the matrix. Additionally, heterologous expression of Prdx3 in yeast revealed that its sorting to the IMS is dependent on the inner membrane peptidase (IMP) complex. Collectively, these findings uncover a complex submitochondrial distribution of Prdx3, supporting its multifaceted role in mitochondrial H2O2 metabolism.

ESF1 and MIPEP proteins promote estrogen receptor-positive breast cancer proliferation and are associated with patient prognosis

BACKGROUND

Estrogen receptor-positive (ER+) breast cancer accounts for two-thirds of all breast cancers, and its early and late recurrences still threaten patients' long-term survival and quality of life. Finding candidate tumor antigens and potential therapeutic targets is critical to addressing these unmet needs.

METHOD

The isobaric tags for relative and absolute quantitation (iTRAQ) proteomic analysis was employed to identify the differentially expressed proteins (DEPs) between ER + breast cancer and corresponding adjacent normal tissue. Candidate DEPs were screened by bioinformatic analyses, and their expression was confirmed by immunohistochemical (IHC) staining and western blot. A series of in vitro experiments, including wound healing assay, colony formation, and cell cycle assay, were performed to reveal the functions of selected DEPs. Additionally, their clinical significances were further analyzed.

RESULT

A total of 369 DEPs (fold change ≥ 2.0 or ≤ 0.66, P < 0.05) were discovered. Compared with normal tissue, 358 proteins were up-regulated and 11 proteins were down-regulated in ER + breast cancer. GO and KEGG enrichment analysis showed that DEPs were closely associated with RNA regulation and metabolic pathways. STRING analysis found ESF1 and MIPEP were the hub genes in breast cancer, whose increased expressions were verified by the IHC staining and western blot. Knocking down ESF1 and MIPEP inhibited colony formation and increased cell apoptosis. Besides, knocking down ESF1 inhibited wound healing but not MIPEP. In addition, ESF1 and MIPEP expression were negatively associated with patient prognosis.

CONCLUSION

The upregulation of ESF1 and MIPEP promoted ER + breast cancer proliferation, which might provide novel targets for the development of new therapies.

Dissecting the molecular mechanisms of mitochondrial import and maturation of peroxiredoxins from yeast and mammalian cells

Peroxiredoxins (Prxs) are cysteine-based peroxidases that play a central role in keeping the H₂O₂ at physiological levels. Eukaryotic cells express different Prxs isoforms, which differ in their subcellular locations and substrate specificities. Mitochondrial Prxs are synthesized in the cytosol as precursor proteins containing N-terminal cleavable presequences that act as mitochondrial targeting signals. Due to the fact that presequence controls the import of the vast majority of mitochondrial matrix proteins, the mitochondrial Prxs were initially predicted to be localized exclusively in the matrix. However, recent studies showed that mitochondrial Prxs are also targeted to the intermembrane space by mechanisms that remain poorly understood. While in yeast the IMP complex can translocate Prx1 to the intermembrane space, the maturation of yeast Prx1 and mammalian Prdx3 and Prdx5 in the matrix has been associated with sequential cleavages of the presequence by MPP and Oct1/MIP proteases. In this review, we describe the state of the art of the molecular mechanisms that control the mitochondrial import and maturation of Prxs of yeast and human cells. Once mitochondria are considered the major intracellular source of H₂O₂, understanding the mitochondrial Prx biogenesis pathways is essential to increase our knowledge about the H₂O₂-dependent cellular signaling, which is relevant to the pathophysiology of some human diseases.

Protein Processing in Plant Mitochondria Compared to Yeast and Mammals

Limited proteolysis, called protein processing, is an essential post-translational mechanism that controls protein localization, activity, and in consequence, function. This process is prevalent for mitochondrial proteins, mainly synthesized as precursor proteins with N-terminal sequences (presequences) that act as targeting signals and are removed upon import into the organelle. Mitochondria have a distinct and highly conserved proteolytic system that includes proteases with sole function in presequence processing and proteases, which show diverse mitochondrial functions with limited proteolysis as an additional one. In virtually all mitochondria, the primary processing of N-terminal signals is catalyzed by the well-characterized mitochondrial processing peptidase (MPP). Subsequently, a second proteolytic cleavage occurs, leading to more stabilized residues at the newly formed N-terminus. Lately, mitochondrial proteases, intermediate cleavage peptidase 55 (ICP55) and octapeptidyl protease 1 (OCT1), involved in proteolytic cleavage after MPP and their substrates have been described in the plant, yeast, and mammalian mitochondria. Mitochondrial proteins can also be processed by removing a peptide from their N- or C-terminus as a maturation step during insertion into the membrane or as a regulatory mechanism in maintaining their function. This type of limited proteolysis is characteristic for processing proteases, such as IMP and rhomboid proteases, or the general mitochondrial quality control proteases ATP23, m-AAA, i-AAA, and OMA1. Identification of processing protease substrates and defining their consensus cleavage motifs is now possible with the help of large-scale quantitative mass spectrometry-based N-terminomics, such as combined fractional diagonal chromatography (COFRADIC), charge-based fractional diagonal chromatography (ChaFRADIC), or terminal amine isotopic labeling of substrates (TAILS). This review summarizes the current knowledge on the characterization of mitochondrial processing peptidases and selected N-terminomics techniques used to uncover protease substrates in the plant, yeast, and mammalian mitochondria.

Peroxiredoxins as Potential Targets for Cardiovascular Disease

Increased oxidative stress (OS) is considered a common etiology in the pathogenesis of cardiovascular disease (CVD). Therefore, the precise regulation of reactive oxygen species (ROS) in cardiovascular cells is essential to maintain normal physiological functions. Numerous regulators of cellular homeostasis are reportedly influenced by ROS. Hydrogen peroxide (H₂O₂), as an endogenous ROS in aerobic cells, is a toxic substance that can induce OS. However, many studies conducted over the past two decades have provided substantial evidence that H₂O₂ acts as a diffusible intracellular signaling messenger. Antioxidant enzymes, including superoxide dismutases, catalase, glutathione peroxidases, and peroxiredoxins (Prdxs), maintain the balance of ROS levels against augmentation of ROS production during the pathogenesis of CVD. Especially, Prdxs are regulatory sensors of transduced intracellular signals. The intracellular abundance of Prdxs that specifically react with H₂O₂ act as regulatory proteins. In this review, we focus on the role of Prdxs in the regulation of ROS-induced pathological changes in the development of CVD.