Intramitochondrial calcium regulation by the FHIT gene product sensitizes to apoptosis

Molecules and roles of mitochondrial calcium signaling

Mitochondrial Ca(2+) homeostasis is an important component of the calcium-mediated cellular response to extracellular stimuli. It controls key organelle functions, such as aerobic metabolism and the induction of apoptotic cell death, and shapes the spatiotemporal pattern of the cytosolic [Ca(2+)] increase. We here summarize both the main roles of Ca(2+) signals within mitochondria and the emerging molecular information that is starting to unravel the composition of the signaling apparatus and reveal potential pharmacological targets in this process of utmost pathophysiological relevance.

IP(3) Receptors, Mitochondria, and Ca Signaling: Implications for Aging

The tight interplay between endoplasmic-reticulum-(ER-) and mitochondria-mediated Ca(2+) signaling is a key determinant of cellular health and cellular fate through the control of apoptosis and autophagy. Proteins that prevent or promote apoptosis and autophagy can affect intracellular Ca(2+) dynamics and homeostasis through binding and modulation of the intracellular Ca(2+)-release and Ca(2+)-uptake mechanisms. During aging, oxidative stress becomes an additional factor that affects ER and mitochondrial function and thus their role in Ca(2+) signaling. Importantly, mitochondrial dysfunction and sustained mitochondrial damage are likely to underlie part of the aging process. In this paper, we will discuss the different mechanisms that control intracellular Ca(2+) signaling with respect to apoptosis and autophagy and review how these processes are affected during aging through accumulation of reactive oxygen species.

Hit proteins, mitochondria and cancer

The histidine triad (HIT) superfamily comprises proteins that share the histidine triad motif, His-ϕ-His-ϕ-His-ϕ-ϕ, where ϕ is a hydrophobic amino acid. HIT proteins are ubiquitous in prokaryotes and eukaryotes. HIT proteins bind nucleotides and exert dinucleotidyl hydrolase, nucleotidylyl transferase or phosphoramidate hydrolase enzymatic activity. In humans, 5 families of HIT proteins are recognized. The accumulated epidemiological and experimental evidence indicates that two branches of the superfamily, the HINT (Histidine Triad Nucleotide Binding) members and FHIT (Fragile Histidine Triad), have tumor suppressor properties but a conclusive physiological role can still not be assigned to these proteins. Aprataxin forms another discrete branch of the HIT superfamily, is implicated in DNA repair mechanisms and unlike the HINT and FHIT members, a defective protein can be conclusively linked to a disease, ataxia with oculomotor apraxia type 1. The scavenger mRNA decapping enzyme, DcpS, forms a fourth branch of the HIT superfamily. Finally, the GalT enzymes, which exert specific nucleoside monophosphate transferase activity, form a fifth branch that is not implicated in tumorigenesis. The molecular mechanisms by which the HINT and FHIT proteins participate in bioenergetics of cancer are just beginning to be unraveled. Their purported actions as tumor suppressors are highlighted in this review.

Pathology and biology associated with the fragile FHIT gene and gene product

More than 12 years and >800 scientific publications after the discovery of the first gene at a chromosome fragile site, the FHIT gene at FRA3B, there are still questions to pursue concerning the selective advantage conferred to cells by loss of expression of FHIT, the most frequent target of allele deletion in precancerous lesions and cancers. These questions are considered in light of recent investigations of genetic and epigenetic alterations to the locus and in a retrospective consideration of biological roles of the Fhit protein discovered through functional studies.

The effects of Fhit on tumorigenesis after multi-exposure to low-dose radiation

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Key Words

• Fhit
• ionizing radiation
• low dose
• tumorigenesis

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Affiliation(s)

Xiaoyan Yu Department of Radiation Oncology, Winship Cancer Institute, Emory UniversityAtlanta, GA 30322, USA Department of Experimental Phamacology and Toxicology, School of Pharmacy, Jilin UniversityChangchun, 130021, China
Lin Lu Department of Radiation Oncology, Thomas Jefferson UniversityPhiladelphia, PA 19107, USA
Siyuan Wen Department of Radiation Oncology, Winship Cancer Institute, Emory UniversityAtlanta, GA 30322, USA Current address: Beijing Institute of Radiation MedicineBeijing 100850, China
Ya Wang Department of Radiation Oncology, Winship Cancer Institute, Emory UniversityAtlanta, GA 30322, USA

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