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Somatostatin analogs stimulate DNA-dependent protein kinase activity in human gastric tumoral cell-line HGT1
Z Sadji1, M Le Romancer, F Hervatin
1Unité de Recherches Biologie et Pathologie de l'Epithélium Digestif, Inserm U10, Hôpital Bichat-Claude Bernard, IFR Cellules Epithéliales, Paris, France. zsadji@bichat.inserm.fr
Abstract:
DNA-dependent protein kinase catalytic subunit (DNA-PKcs) phosphorylates, in the presence of double-stranded DNA, several transcription-, replication- and repair -factors. Its interaction with the DNA-binding regulatory component Ku (p86-/p70-Ku) is required for stabilization and activity. We have previously shown that p86-Ku behaves as a specific receptor for the growth inhibitory tetradecapeptide, somatostatin. In this work, we investigate a possible regulation by somatostatin analogs, of DNA-PK activity in the human gastric tumoral HGT1/clone6 cell-line. We demonstrate that a 48 h-preincubation of cells with octreotide or RC-160, stimulates DNA-PK activity by 8 and 10 fold with ED50s of 1 and 0.1 nM, respectively. These stimulations appearing only after 3 h were inhibited by cycloheximide. They were not observed in a cell clone which was transfected by a cDNA encoding p86-Ku antisense. This study demonstrates the existence of a new somatostatin signaling pathway involving the stimulation of DNA-PK activity.
Insights
Somatostatin analogs like octreotide and RC-160 stimulate DNA-dependent protein kinase catalytic subunit (DNA-PKcs) activity in gastric cancer cells. This novel signaling pathway involves the p86-Ku receptor and protein synthesis.
Area of Science:
- Molecular Biology
- Cell Biology
- Biochemistry
Background:
- DNA-dependent protein kinase catalytic subunit (DNA-PKcs) is crucial for DNA repair, replication, and transcription.
- DNA-PKcs activity requires interaction with the Ku protein complex (p86/p70-Ku).
- The p86-Ku subunit acts as a specific receptor for the growth-inhibitory peptide somatostatin.
Purpose of the Study:
- To investigate the regulation of DNA-PK activity by somatostatin analogs in human gastric tumoral HGT1/clone6 cells.
- To elucidate the role of the p86-Ku subunit in this regulatory pathway.
Main Methods:
- Cell culture of HGT1/clone6 human gastric cancer cells.
- Preincubation of cells with somatostatin analogs (octreotide, RC-160).
- Assessment of DNA-PK activity.
- Inhibition studies using cycloheximide.
- Transfection with p86-Ku antisense cDNA.
Main Results:
- Octreotide and RC-160 significantly stimulated DNA-PK activity in a dose- and time-dependent manner (8-10 fold stimulation).
- Stimulation was dependent on protein synthesis, as indicated by cycloheximide inhibition.
- The stimulatory effect was abolished in cells expressing p86-Ku antisense, confirming the role of p86-Ku.
Conclusions:
- A novel somatostatin signaling pathway exists that stimulates DNA-PK activity.
- This pathway is mediated by the p86-Ku subunit and involves newly synthesized proteins.
- Findings suggest a new mechanism for regulating DNA-PK activity in cancer cells.