Somatostatin analogs stimulate DNA-dependent protein kinase activity in human gastric tumoral cell-line HGT1

DNA-PKcs modulates mouse lung homeostasis via the regulation of mitochondrial fission

BACKGROUND

The role of DNA-dependent protein kinase catalytic subunit (DNA-PKcs) is multifaceted, paradoxically promoting both cell survival and cell death across multiple organs. However, its impact on lung homeostasis remains elusive. Here, we investigate the function of DNA-PKcs in mouse lungs, aiming to elucidate its role for lung abnormalities associated with DNA-PKcs deficiency.

MATERIALS AND METHODS

Histological assessment and immunohistochemistry were used to reveal the pathological changes of the lungs in DNA-PKcs-deficient mice. Transcriptomic analysis identified differentially expressed genes and pathways in DNA-PKcs-deficient lungs. Furthermore, mitochondrial dysfunction induced by DNA-PKcs deficiency was investigated by qPCR and immunoblotting. Mouse primary lung fibroblasts were used to evaluate the potential therapeutic effect of inhibiting mitochondrial fission with Mdivi-1.

KEY FINDINGS

In DNA-PKcs-deficient mouse lungs, we observed pathological changes including alveolar septal thickening, capillary congestion and hemorrhage, along with lung cell proliferation. Transcriptome analysis revealed an upregulation of the reactive oxygen species (ROS) biosynthesis process and the apoptotic signaling pathway caused by DNA-PKcs deficiency. Further investigations demonstrated that DNA-PKcs deficiency led to mitochondrial dysfunction and increased oxidative stress, along with increased cell apoptosis in the mouse lungs. Notably, we detected enhanced phosphorylation of the mitochondrial fission protein DRP1 in DNA-PKcs-deficient mouse lungs. Intriguingly, inhibiting mitochondrial fission using Mdivi-1 suppressed cell death in primary mouse lung fibroblasts with siRNA-mediated DNA-PKcs knockdown.

SIGNIFICANCE

Our study provides insights into the crucial role of DNA-PKcs in sustaining lung homeostasis via the maintenance of mitochondrial functionality and provides a therapeutic strategy targeting mitochondrial fission against DNA-PKcs deficiency-associated lung diseases.

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Somatostatin-induced regulation of SST(2A) receptor expression and cellsurface availability in central neurons: role of receptor internalization

To investigate the effects of somatostatin (somatotropin release-inhibiting factor, SRIF) on the regulation of SST(2A) receptors in mammalian brain, we examined how blockade of SRIF release or stimulation by the SRIF analog [d-Trp(8)]-SRIF would affect the expression and cell surface availability of SST(2A) receptors in rat brain slices. First, we measured the intensity of SST(2A) immunoreactivity, using quantitative light microscopic immunocytochemistry, and levels of SST(2A) mRNA, using semiquantitative RT-PCR, under conditions of acute SRIF release blockade. Incubation of slices from the claustrum or basolateral amygdala, two regions previously shown to contain high concentrations of SST(2A) receptors, in Ca(2+)-free Ringer's for 40 min induced a decrease in the intensity of SST(2A) receptor immunoreactivity and concentration of SST(2A) mRNA as compared with control values obtained in Ca(2+)-supplemented Ringer's. These effects were counteracted in a dose-dependent manner by the addition of 10-100 nm [d-Trp(8)]-SRIF to the Ca(2+)-free medium. Furthermore, both of these effects were abolished in the presence of the endocytosis inhibitors phenylarsine oxide or hyperosmolar sucrose, suggesting that they were dependent on receptor internalization. Electron microscopic immunogold labeling confirmed the existence of an agonist-induced internalization of SST(2A) receptors in central neurons. At a high (10 microm), but not at a low (10 nm), concentration of agonist this internalization resulted in a significant decrease in cell surface receptor density, irrespective of the presence of Ca(2+) in the medium. Taken together, these results suggest that ligand-induced endocytosis is responsible for rapid transcriptional (increase in SST(2A) expression) and trafficking (loss of cell surface receptors) events involved in the control of the somatostatinergic signal.