Outlining the Complex Pathway of Mammalian Fe-S Cluster Biogenesis

Iron-sulfur (Fe-S) clusters (ISCs) are ubiquitous cofactors essential to numerous fundamental cellular processes. Assembly of ISCs and their insertion into apoproteins involves the function of complex cellular machineries that operate in parallel in the mitochondrial and cytosolic/nuclear compartments of mammalian cells. The spectrum of diseases caused by inherited defects in genes that encode the Fe-S assembly proteins has recently expanded to include multiple rare human diseases, which manifest distinctive combinations and severities of global and tissue-specific impairments. In this review, we provide an overview of our understanding of ISC biogenesis in mammalian cells, discuss recent work that has shed light on the molecular interactions that govern ISC assembly, and focus on human diseases caused by failures of the biogenesis pathway.

An Oxygen-Dependent Interaction between FBXL5 and the CIA-Targeting Complex Regulates Iron Homeostasis

The iron-sensing protein FBXL5 is the substrate adaptor for a SKP1-CUL1-RBX1 E3 ubiquitin ligase complex that regulates the degradation of iron regulatory proteins (IRPs). Here, we describe a mechanism of FBXL5 regulation involving its interaction with the cytosolic Fe-S cluster assembly (CIA) targeting complex composed of MMS19, FAM96B, and CIAO1. We demonstrate that the CIA-targeting complex promotes the ability of FBXL5 to degrade IRPs. In addition, the FBXL5-CIA-targeting complex interaction is regulated by oxygen (O₂) tension displaying a robust association in 21% O₂ that is severely diminished in 1% O₂ and contributes to O₂-dependent regulation of IRP degradation. Together, these data identify a novel oxygen-dependent signaling axis that links IRP-dependent iron homeostasis with the Fe-S cluster assembly machinery.

Identification of FAM96B as a novel prelamin A binding partner

Prelamin A accumulation causes nuclear abnormalities, impairs nuclear functions, and eventually promotes cellular senescence. However, the underlying mechanism of how prelamin A promotes cellular senescence is still poorly understood. Here we carried out a yeast two-hybrid screen using a human skeletal muscle cDNA library to search for prelamin A binding partners, and identified FAM96B as a prelamin A binding partner. The interaction of FAM96B with prelamin A was confirmed by GST pull-down and co-immunoprecipitation experiments. Furthermore, co-localization experiments by fluorescent confocal microscopy revealed that FAM96B colocalized with prelamin A in HEK-293 cells. Taken together, our data demonstrated the physical interaction between FAM96B and prelamin A, which may provide some clues to the mechanisms of prelamin A in premature aging.

FAM96A and FAM96B function as new tumor suppressor genes in breast cancer through regulation of the Wnt/β-catenin signaling pathway

AIMS

Family with sequence similarity 96 member A and B (FAM96A and FAM96B) are two highly conserved homologous proteins belonging to MIP18 family. Some studies have shown that FAM96A and FAM96B are significantly down-regulated in human gastrointestinal stromal tumors, colon cancer, and liver cancer. However, the molecular mechanisms of FAM96A/B in breast cancer are unknown. This work aims to explore the roles of FAM96A/B in breast cancer progression.

MAIN METHODS

Specific siRNAs were used to down-regulate FAM96A/B expression, and recombinant plasmids were used to up-regulate FAM96A/B expression in breast cancer cells. Cell proliferation was measured using MTT and colony formation. Cell cycle and apoptosis were detected by flow cytometry. Cell migration and invasion were examined by wound healing and transwell assays. The relationships among FAM96A/B, EMT and Wnt/β-catenin pathway were determined by analyzing expression changes of classical markers.

KEY FINDINGS

We found that FAM96A/B expression was down-regulated in breast cancer. FAM96A/B overexpression suppressed breast cancer cell proliferation, invasion and migration, induced cell apoptosis and caused cell cycle arrest. Conversely, FAM96A/B knockdown exhibited the opposite effects. Moreover, our data demonstrated that FAM96A/B overexpression suppressed EMT and Wnt/β-catenin pathway, while FAM96A/B knockdown showed the promoting effects on EMT and Wnt/β-catenin pathway. Furthermore, a Wnt pathway inhibitor, XAV-939 reversed the promoting effects of FAM96A/B knockdown on breast cancer progression.

SIGNIFICANCE

Our findings suggest that FAM96A/B may function as new tumor suppressor genes and inhibit breast cancer progression via modulating Wnt/β-catenin pathway, which can provide the potential markers for breast cancer diagnosis and therapy.

FAM96B negatively regulates FOSL1 to modulate the osteogenic differentiation and regeneration of periodontal ligament stem cells via ferroptosis

BACKGROUND

Periodontal ligament stem cell (PDLSC)-based therapy is one of the methods to assist bone regeneration. Understanding the functional regulation of PDLSCs and the mechanisms involved is a crucial issue in bone regeneration. This study aimed to explore the roles of the family with sequence similarity 96 member B (FAM96B) in the functional regulation of PDLSCs.

METHODS

To assess the osteogenic differentiation of PDLSCs, the alkaline phosphatase (ALP) activity assay, Alizarin red staining, quantitative calcium analysis, and osteogenic marker detection were conducted. Transplantation PDLSCs under the dorsum of nude mice and into the rat calvarial defects were also performed. Then, FAM96B-overexpressed PDLSCs were used for RNA-sequencing and bioinformatic analysis. To evaluate the ferroptosis of PDLSCs, cytosolic reactive oxygen species (ROS), expression of glutathione peroxidase 4 (GPX4), mitochondrial morphology and functions including the mitochondrial ROS, mitochondria membrane potential, and mitochondrial respiration were detected.

RESULTS

The osteogenic indicators ALP activity, level of mineralization, and osteocalcin expression were decreased in PDLSCs by FAM96B, which demonstrated that FAM96B inhibited the osteogenic differentiation of PDLSCs. FAM96B knockdown promoted the new bone formation of PDLSCs subcutaneously transplanted to the dorsum of nude mice. Then, related biological functions were detected by the RNA-sequencing and the ferroptosis was focused. FAM96B enhanced the cytosolic ROS level and inhibited the expression of GPX4 and mitochondrial functions in PDLSCs. Hence, FAM96B promoted the ferroptosis of PDLSCs. Meanwhile, we found that FAM96B inhibition upregulated the target gene FOS like 1, AP-1 transcription factor subunit (FOSL1) expression and FOSL1 promoted the osteogenic differentiation of PDLSCs in vitro. FOSL1 also promoted the new bone formation of PDLSCs transplanted subcutaneously to the dorsum of nude mice and transplanted into rat calvarial defects. Then, the inhibitory effect of FOSL1 on the ferroptosis was confirmed.

CONCLUSIONS

FAM96B depletion promoted the osteogenic differentiation and suppressed the ferroptosis of PDLSCs. FAM96B negatively regulated the downstream gene FOSL1 and FOSL1 promoted the osteogenic differentiation of PDLSCs via the ferroptosis. Hence, our findings provided a foundation for understanding the FAM96B-FOSL1 axis acting as a target for MSC mediated bone regeneration.

Iron‑sulfur clusters in viral proteins: Exploring their elusive nature, roles and new avenues for targeting infections

Viruses have evolved complex mechanisms to exploit host factors for replication and assembly. In response, host cells have developed strategies to block viruses, engaging in a continuous co-evolutionary battle. This dynamic interaction often revolves around the competition for essential resources necessary for both host cell and virus replication. Notably, iron, required for the biosynthesis of several cofactors, including iron‑sulfur (FeS) clusters, represents a critical element in the ongoing competition for resources between infectious agents and host. Although several recent studies have identified FeS cofactors at the core of virus replication machineries, our understanding of their specific roles and the cellular processes responsible for their incorporation into viral proteins remains limited. This review aims to consolidate our current knowledge of viral components that have been characterized as FeS proteins and elucidate how viruses harness these versatile cofactors to their benefit. Its objective is also to propose that viruses may depend on incorporation of FeS cofactors more extensively than is currently known. This has the potential to revolutionize our understanding of viral replication, thereby carrying significant implications for the development of strategies to target infections.