Parkin gene mutations are not common, but its epigenetic inactivation is a frequent event and predicts poor survival in advanced breast cancer patients

Deficiency in the mitophagy mediator Parkin accelerates murine skin allograft rejection

Alterations in mitochondrial function and associated quality control programs, including mitochondrial-specific autophagy, termed mitophagy, are gaining increasing recognition in the context of disease. However, the role of mitophagy in organ transplant rejection remains poorly understood. Using mice deficient in Parkin, a ubiquitin ligase that tags damaged or dysfunctional mitochondria for autophagic clearance, we assessed the impact of Parkin-dependent mitophagy on skin-graft rejection. We observed accelerated graft loss in Parkin-deficient mice across multiple skin graft models. Immune cell distributions posttransplant were largely unperturbed compared to wild-type; however, the CD8+ T cells of Parkin-deficient mice expressed more T-bet, IFNγ, and Ki67, indicating greater priming toward effector function. This was accompanied by increased circulating levels of IL-12p70 in Parkin-deficient mice. Using a mixed leukocyte reaction, we demonstrated that naïve Parkin-deficient CD4+ and CD8+ T cells exhibit enhanced activation marker expression and proliferative responses to alloantigen, which were attenuated with administration of a pharmacological mitophagy inducer (p62-mediated mitophagy inducer), known to increase mitophagy in the absence of a functional PINK1-Parkin pathway. These findings indicate a role for Parkin-dependent mitophagy in curtailing skin-graft rejection.

Parkin deficiency promotes liver cancer metastasis by TMEFF1 transcription activation via TGF-β/Smad2/3 pathway

Parkin (PARK2) deficiency is frequently observed in various cancers and potentially promotes tumor progression. Here, we showed that Parkin expression is downregulated in liver cancer tissues, which correlates with poor patient survival. Parkin deficiency in liver cancer cells promotes migration and metastasis as well as changes in EMT and metastasis markers. A negative correlation exists between TMEFF1 and Parkin expression in liver cancer cells and tumor tissues. Parkin deficiency leads to upregulation of TMEFF1 which promotes migration and metastasis. TMEFF1 transcription is activated by Parkin-induced endogenous TGF-β production and subsequent phosphorylation of Smad2/3 and its binding to TMEFF1 promotor. TGF-β inhibitor and TMEFF1 knockdown can reverse shParkin-induced cell migration and changes of EMT markers. Parkin interacts with and promotes the ubiquitin-dependent degradation of HIF-1α/HIF-1β and p53, which accounts for the suppression of TGF-β production. Our data have revealed that Parkin deficiency in cancer leads to the activation of the TGF-β/Smad2/3 pathway, resulting in the expression of TMEFF1 which promotes cell migration, EMT, and metastasis in liver cancer cells.

Unconventional protein post-translational modifications: the helmsmen in breast cancer

Breast cancer is the most prevalent malignant tumor and a leading cause of mortality among females worldwide. The tumorigenesis and progression of breast cancer involve complex pathophysiological processes, which may be mediated by post-translational modifications (PTMs) of proteins, stimulated by various genes and signaling pathways. Studies into PTMs have long been dominated by the investigation of protein phosphorylation and histone epigenetic modifications. However, with great advances in proteomic techniques, several other PTMs, such as acetylation, glycosylation, sumoylation, methylation, ubiquitination, citrullination, and palmitoylation have been confirmed in breast cancer. Nevertheless, the mechanisms, effects, and inhibitors of these unconventional PTMs (particularly, the non-histone modifications other than phosphorylation) received comparatively little attention. Therefore, in this review, we illustrate the functions of these PTMs and highlight their impact on the oncogenesis and progression of breast cancer. Identification of novel potential therapeutic drugs targeting PTMs and development of biological markers for the detection of breast cancer would be significantly valuable for the efficient selection of therapeutic regimens and prediction of disease prognosis in patients with breast cancer.

The RING finger protein family in health and disease

Ubiquitination is a highly conserved and fundamental posttranslational modification (PTM) in all eukaryotes regulating thousands of proteins. The RING (really interesting new gene) finger (RNF) protein, containing the RING domain, exerts E3 ubiquitin ligase that mediates the covalent attachment of ubiquitin (Ub) to target proteins. Multiple reviews have summarized the critical roles of the tripartite-motif (TRIM) protein family, a subgroup of RNF proteins, in various diseases, including cancer, inflammatory, infectious, and neuropsychiatric disorders. Except for TRIMs, since numerous studies over the past decades have delineated that other RNF proteins also exert widespread involvement in several diseases, their importance should not be underestimated. This review summarizes the potential contribution of dysregulated RNF proteins, except for TRIMs, to the pathogenesis of some diseases, including cancer, autoimmune diseases, and neurodegenerative disorder. Since viral infection is broadly involved in the induction and development of those diseases, this manuscript also highlights the regulatory roles of RNF proteins, excluding TRIMs, in the antiviral immune responses. In addition, we further discuss the potential intervention strategies targeting other RNF proteins for the prevention and therapeutics of those human diseases.

KMT2C is a potential biomarker of prognosis and chemotherapy sensitivity in breast cancer

PURPOSE

Epigenetic regulation plays critical roles in cancer progression, and high-frequency mutations or expression variations in epigenetic regulators have been frequently observed in tumorigenesis, serving as biomarkers and targets for cancer therapy. Here, we aimed to explore the function of epigenetic regulators in breast cancer.

METHODS

The mutational landscape of epigenetic regulators in breast cancer samples was investigated based on datasets from the Cancer Genome Atlas. The Kaplan-Meier method was used for survival analysis. RNA sequencing (RNA-seq) in MCF-7 cells transfected with control siRNA or KMT2C siRNA was performed. Quantitative reverse transcription-PCR and chromatin immunoprecipitation were used to validate the RNA-seq results.

RESULTS

Among the 450 epigenetic regulators, KMT2C was frequently mutated in breast cancer samples. The tumor mutational burden (TMB) was elevated in breast cancer samples with KMT2C mutations or low KMT2C mRNA levels compared to their counterparts with wild-type KMT2C or high KMT2C mRNA levels. Somatic mutation and low expression of KMT2C were independently correlated with the poor overall survival (OS) and disease-free survival (DFS) of the breast cancer samples, respectively. RNA-seq analysis combined with chromatin immunoprecipitation and qRT-PCR assays revealed that the depletion of KMT2C remarkably affected the expression of DNA damage repair-related genes. More importantly, the low expression of KMT2C was related to breast cancer cell sensitivity to chemotherapy and longer OS of breast cancer patients who underwent chemotherapy.

CONCLUSION

We conclude that KMT2C could serve as a potential biomarker of prognosis and chemotherapy sensitivity by affecting the DNA damage repair-related genes of breast cancer.

Regulation of Parkin expression as the key balance between neural survival and cancer cell death

Parkin is a cytosolic E3 ubiquitin ligase that plays an important role in neuroprotection by targeting several proteins to be degraded by the 26S proteasome. Its dysfunction has been associated not only with Parkinson's disease (PD) but also with other neurodegenerative pathologies, such as Alzheimer's disease and Huntington's disease. More recently, Parkin has been identified as a tumor suppressor gene implicated in cancer development. Due to the important roles that this E3 ubiquitin ligase plays in cellular homeostasis, its expression, activity, and turnover are tightly regulated. Several reviews have addressed Parkin regulation; however, genetic and epigenetic regulation have been excluded. In addition to posttranslational modifications (PTMs), this review examines the regulatory mechanisms that control Parkin function through gene expression, epigenetic regulation, and degradation. Furthermore, the consequences of disrupting these regulatory processes on human health are discussed.

Parkin: A targetable linchpin in human malignancies

Parkin, an E3 ubiquitin ligase has been found to be deregulated in a variety of human cancers. Our current understanding is endowed with strong evidences that Parkin plays crucial role in the pathogenesis of cancer by controlling/interfering with major hallmarks of cancer delineated till today. Consistent with the idea of mitophagy, the existing studies imitates the tumor suppressive potential of Parkin, resolved by its capacity to regulate cell proliferation, cell migration, angiogenesis, apoptosis and overall cellular survival. Dysfunction of Parkin has resulted in the loss of ubiquitination of cell cycle components followed by their accumulation leading to genomic instability, perturbed cell cycle and eventually tumor progression. In this review, we provide an overview of current knowledge about the critical role of Parkin in cancer development and progression and have focussed on its therapeutic implications highlighting the diagnostic and prognostic value of Parkin as a biomarker. We earnestly hope that an in-depth knowledge of Parkin will provide a linchpin to target in various cancers that will open a new door of clinical applications and therapeutics.

Clinical Significance of Receptor-Interacting Protein 3 and Parkin, Essential Molecules for Necroptosis, in Breast Cancer

Purpose

Receptor-interacting protein 3 (RIP3) is the main initiator of necroptosis. Parkin prevents the formation of the RIP1–RIP3 complex by promoting polyubiquitination of RIP3. However, the mechanism by which necroptosis affects the clinical features of breast cancer and prognosis is not known. Here, we aimed to study the effect of necroptosis on the clinical features and prognosis of breast cancer by assessing the expression of RIP3 and Parkin.

Methods

Tissue microarrays (TMAs) were constructed from 257 cases of breast cancer. Immunohistochemistry was performed on 4-μm tissue sections from each TMA block. The χ² test, Kaplan-Meier survival analysis with log-rank test, and Cox regression proportional hazard model were used for statistical analysis.

Results

Low RIP3 expression resulted in a large tumor size and high nuclear grade. Low RIP3 expression was correlated with human epidermal growth factor receptor 2 positivity, short overall survival (OS), and short disease-free survival (DFS). The triple negative breast cancer group with low RIP3 expression and lymph node (LN) positive group with low RIP3 expression had the shortest OS. High Parkin expression was associated with high histological grade, estrogen and/or progesterone receptor negativity, and lymphatic emboli, but was not correlated with OS and DFS. OS was correlated with LN metastasis and RIP3 loss and DFS with large tumor size, LN metastasis, and RIP3 loss.

Conclusion

Low RIP3 and high Parkin expression are associated with aggressive clinical features in breast cancer. RIP3, a molecular marker of necroptosis, is an independent factor associated with survival in breast cancer. Further in-depth studies are needed to investigate the role of necroptosis in breast cancer development, metastasis, and treatment in the future.

Mitochondria as the decision makers for cancer cell fate: from signaling pathways to therapeutic strategies

As pivotal players in cellular metabolism, mitochondria have a double-faceted role in the final decision of cell fate. This is true for all cell types, but it is even more important and intriguing in the cancer setting. Mitochondria regulate cell fate in many diverse ways: through metabolism, by producing ATP and other metabolites deemed vital or detrimental for cancer cells; through the regulation of Ca²⁺ homeostasis, especially by the joint participation of the endoplasmic reticulum in a membranous tethering system for Ca²⁺ signaling called mitochondria-ER associated membranes (MAMs); and by regulating signaling pathways involved in the survival of cancer cells such as mitophagy. Recent studies have shown that mitochondria can also play a role in the regulation of inflammatory pathways in cancer cells, for example, through the release of mitochondrial DNA (mtDNA) involved in the activation of the cGAS-cGAMP-STING pathway. In this review, we aim to explore the role of mitochondria as decision makers in fostering cancer cell death or survival depending on the tumor cell stage and describe novel anticancer therapeutic strategies targeting mitochondria.

The Links between Parkinson's Disease and Cancer

Epidemiologic studies indicate a decreased incidence of most cancer types in Parkinson’s disease (PD) patients. However, some neoplasms are associated with a higher risk of occurrence in PD patients. Both pathologies share some common biological pathways. Although the etiologies of PD and cancer are multifactorial, some factors associated with PD, such as α-synuclein aggregation; mutations of PINK1, PARKIN, and DJ-1; mitochondrial dysfunction; and oxidative stress can also be involved in cancer proliferation or cancer suppression. The main protein associated with PD, i.e., α-synuclein, can be involved in some types of neoplastic formations. On the other hand, however, its downregulation has been found in the other cancers. PINK1 can act as oncogenic or a tumor suppressor. PARKIN dysfunction may lead to some cancers’ growth, and its expression may be associated with some tumors’ suppression. DJ-1 mutation is involved in PD pathogenesis, but its increased expression was found in some neoplasms, such as melanoma or breast, lung, colorectal, uterine, hepatocellular, and nasopharyngeal cancers. Both mitochondrial dysfunction and oxidative stress are involved in PD and cancer development. The aim of this review is to summarize the possible associations between PD and carcinogenesis.

RBR E3 ubiquitin ligases in tumorigenesis

RING-in-between-RING (RBR) E3 ligases are one class of E3 ligases that is characterized by the unique RING-HECT hybrid mechanism to function with E2s to transfer ubiquitin to target proteins for degradation. Emerging evidence has demonstrated that RBR E3 ligases play essential roles in neurodegenerative diseases, infection, inflammation and cancer. Accumulated evidence has revealed that RBR E3 ligases exert their biological functions in various types of cancers by modulating the degradation of tumor promoters or suppressors. Hence, we summarize the differential functions of RBR E3 ligases in a variety of human cancers. In general, ARIH1, RNF14, RNF31, RNF144B, RNF216, and RBCK1 exhibit primarily oncogenic roles, whereas ARIH2, PARC and PARK2 mainly have tumor suppressive functions. Moreover, the underlying mechanisms by which different RBR E3 ligases are involved in tumorigenesis and progression are also described. We discuss the further investigation is required to comprehensively understand the critical role of RBR E3 ligases in carcinogenesis. We hope our review can stimulate the researchers to deeper explore the mechanism of RBR E3 ligases-mediated carcinogenesis and to develop useful inhibitors of these oncogenic E3 ligases for cancer therapy.

Implication of alterations in Parkin gene among North Indian patients with colorectal cancer

BACKGROUND/AIMS

Alterations in Parkin (PRKN) have been described in many cancers; however, the molecular mechanism that contributes to loss of Parkin expression in colorectal cancer (CRC) remains unclear. The aim of this study was to investigate the involvement of PRKN mutation and loss of heterozygosity (LOH) in loss of Parkin expression. To understand the role of PRKN in cancer progression, we also evaluated the association of Parkin expression with clinicopathological parameters in North Indian population.

MATERIALS AND METHODS

We studied 219 CRC samples and their adjacent normal tissues (control) obtained from North Indian patients with CRC. The expression of Parkin was analyzed by immunohistochemistry (IHC). PRKN mutations were analyzed by single-stranded conformational polymorphism (SSCP) and sequencing. For loss of heterozygosity (LOH), we employed two intragenic, D6S305 and D6S1599, and one telomeric marker, D6S1008.

RESULTS

In our study, we found four novel somatic mutations, namely, C166G, K413N, R420P (exon 4), and V425E (exon 11). Both mutation in Parkin (p = 0.0014) and LOH (p = 0.0140) were significantly associated with loss of Parkin expression. Additionally, Parkin mutations were not associated with the clinicopathological parameters of the patients. Furthermore, both, LOH in Parkin and Parkin expression were significantly correlated with different clinicopathological variables (p<0.05).

CONCLUSION

Our results indicate that Parkin expression is not regulated by a single mechanism, but both mutation and LOH contribute to loss of Parkin expression. We also provide evidence of involvement of Parkin in metastasis and cancer progression. We, therefore, suggest Parkin as a potential prognostic marker and warrant further analysis in this direction.

Aconitase 2 inhibits the proliferation of MCF-7 cells promoting mitochondrial oxidative metabolism and ROS/FoxO1-mediated autophagic response

Background

Deregulation of the tricarboxylic acid cycle (TCA) due to mutations in specific enzymes or defective aerobic metabolism is associated with tumour growth. Aconitase 2 (ACO2) participates in the TCA cycle by converting citrate to isocitrate, but no evident demonstrations of its involvement in cancer metabolism have been provided so far.

Methods

Biochemical assays coupled with molecular biology, in silico, and cellular tools were applied to circumstantiate the impact of ACO2 in the breast cancer cell line MCF-7 metabolism. Fluorescence lifetime imaging microscopy (FLIM) of NADH was used to corroborate the changes in bioenergetics.

Results

We showed that ACO2 levels are decreased in breast cancer cell lines and human tumour biopsies. We generated ACO2- overexpressing MCF-7 cells and employed comparative analyses to identify metabolic adaptations. We found that increased ACO2 expression impairs cell proliferation and commits cells to redirect pyruvate to mitochondria, which weakens Warburg-like bioenergetic features. We also demonstrated that the enhancement of oxidative metabolism was supported by mitochondrial biogenesis and FoxO1-mediated autophagy/mitophagy that sustains the increased ROS burst.

Conclusions

This work identifies ACO2 as a relevant gene in cancer metabolic rewiring of MCF-7 cells, promoting a different utilisation of pyruvate and revealing the potential metabolic vulnerability of ACO2-associated malignancies.