Apoptosis inhibitor of macrophage protein enhances intraluminal debris clearance and ameliorates acute kidney injury in mice.

Acute kidney injury (AKI) is associated with prolonged hospitalization and high mortality, and it predisposes individuals to chronic kidney disease. To date, no effective AKI treatments have been established. Here we show that the apoptosis inhibitor of macrophage (AIM) protein on intraluminal debris interacts with kidney injury molecule (KIM)-1 and promotes recovery from AKI. During AKI, the concentration of AIM increases in the urine, and AIM accumulates on necrotic cell debris within the kidney proximal tubules. The AIM present in this cellular debris binds to KIM-1, which is expressed on injured tubular epithelial cells, and enhances the phagocytic removal of the debris by the epithelial cells, thus contributing to kidney tissue repair. When subjected to ischemia-reperfusion (IR)-induced AKI, AIM-deficient mice exhibited abrogated debris clearance and persistent renal inflammation, resulting in higher mortality than wild-type (WT) mice due to progressive renal dysfunction. Treatment of mice with IR-induced AKI using recombinant AIM resulted in the removal of the debris, thereby ameliorating renal pathology. We observed this effect in both AIM-deficient and WT mice, but not in KIM-1-deficient mice. Our findings provide a basis for the development of potentially novel therapies for AKI.

Circulating AIM prevents hepatocellular carcinoma through complement activation.

Hepatocellular carcinoma (HCC) is a widespread fatal disease and the third most common cause of cancer deaths. Here, we show the potent anti-HCC effect of the circulating protein AIM. As in adipocytes, AIM is incorporated into normal hepatocytes, where it interferes with lipid storage. In contrast, AIM accumulates on the HCC cell surface and activates the complement cascade via inactivating multiple regulators of complement activation. This response provokes necrotic cell death specifically in AIM-bound HCC cells. Accordingly, AIM(-/-) mice were highly susceptible to steatosis-associated HCC development, whereas no AIM(+/+) mouse developed the disease despite comparable liver inflammation and fibrosis in response to a long-term high-fat diet. Administration of AIM prevented tumor development in AIM(-/-) mice, and HCC induction by diethylnitrosamine was more prominent in AIM(-/-) than wild-type mice. These findings could be the basis for novel AIM-based therapeutic strategies for HCC.

Interaction of human minichromosome maintenance protein-binding protein with minichromosome maintenance 2-7.

It has been reported that minichromosome maintenance protein-binding protein (MCM-BP) functions in the formation of the pre-replication complex, unloading of minichromosome maintenance (MCM)2-7 from chromatin in late S phase, and formation of the cohesion complex by interacting with MCM3-7 proteins, suggesting that MCM-BP functions in several different reactions during the cell cycle. Here, we examined the interaction of human MCM-BP with MCM2-7 and structural maintenance of chromosome 3 in synchronized HeLa cells by immunoprecipitation. The results show that MCM-BP mainly interacts with MCM7 in the Triton-soluble fraction from S phase and G(2) phase cells, and it also interacts with structural maintenance of chromosome 3 in the fraction from G(2) phase cells. In vitro studies show that MCM-BP disassembles MCM2-7 bound to DNA with a fork-like structure by interacting with MCM3, MCM5, and MCM7. These results suggest that MCM-BP functions in disassembling MCM2-7 on chromatin during S phase and G2 phase by interacting with MCM3, MCM5, and MCM7.

Protein interaction and cellular localization of human CDC45.

CDC45, which plays a role in eukaryotic DNA replication, is a member of the CMG (CDC45/MCM2-7/GINS) complex that is thought to function as a replicative DNA helicase. However, the biochemical properties of CDC45 are not fully understood. We systematically examined the interactions of human CDC45 with MCM2-7, GINS and other replication proteins by immunoprecipitation. We found that CDC45 can directly interact with all MCM2-7 proteins; with PSF2, PSF3 and SLD5 in GINS subunits; and with replication protein A2 (RPA2), AND-1 and topoisomerase 2-binding protein 1. These results are consistent with the notion that CDC45 plays a role in progression of DNA replication forks. Experiments using antibodies against CDC45 show that the level of CDC45 recovered from the Triton-insoluble chromatin-containing fraction is peaked at middle of S phase in synchronized HeLa cells. However, incubation of the Triton-insoluble fraction with nucleases resulted in recovery of less than half the amount of CDC45 in the nuclease-sensitive fraction; this result is in contrast with RPA1 and proliferating cell nuclear antigen distribution. These results indicate that a considerable portion of CDC45 localizes in a region other than the DNA replication forks in nuclei or it localizes on the replication forks but it is not fractionated with the fork proteins owing to its tight association with presumably nuclear scaffolds.