LRP16 gene protects mouse insulinoma MIN6 cells against fatty acid-induced apoptosis through Akt/FoxO1 signaling.
BACKGROUND
Pancreatic β cells are susceptible to fatty acid-induced apoptosis. The 17β-estradiol (E2) protects pancreatic β cells from apoptosis, mediated by the estrogen receptor-α (ERα). The mRNA level and promoter activity of leukemia-related protein (LRP) 16 were significantly increased by E2 in ER-α and LRP16 was a co-activator of ER-α. The aim of the study was to assess the effects of LRP16 on fatty acid-induced apoptosis in MIN6 cells.


METHODS
Cells with over-expressing LRP16 were obtained by lipidosome transfection. Insulin content and glucose-stimulated insulin secretion (GSIS) were examined by radioimmunoassay. Western blotting was applied to detect protein expression. Apoptosis was detected by terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) and flow cytometry. The forkhead boxO1 (FoxO1) subcellular localization was determined by immunocytochemical analysis.


RESULTS
MIN6-LRP16 cells with overexpression of LRP16 were successfully established, and protein expression of LRP16 was 2.29-fold of that of control cells (MIN6-3.1, P < 0.05). Insulin content and GSIS in MIN6-LRP16 were substantially increased compared with those in control cells. When cells were stimulated with glucose, increased phosphorylation of extracellular signal-regulated kinase (ERK) 1/2 and serine-threonine kinase (Akt) were observed in MIN6-LRP16. When cells were under palmitate pressure, the TUNEL-positive rate in MIN6-LRP16 was (17.0 ± 0.5)%, while it in MIN6-3.1 was (22.0 ± 0.4)%. In palmitate-treated cells, attenuated Akt phosphorylation was observed, but the attenuation in Akt activity was partially restored in MIN6-LRP16 cells. Meanwhile, nuclear localization of FoxO1 in MIN6-LRP16 was apparently reduced compared with that in control cells.


CONCLUSIONS
LRP16 regulated insulin content and GSIS in MIN6 cells by ERK1/2 and Akt activated way. Meanwhile, LRP16 overexpression protected MIN6 cells from fatty acid-induced apoptosis by partially restoring Akt phosphorylation and inhibiting FoxO1 nuclear redistribution. Therefore, LRP16 played important roles not only in insulin content and GSIS but also in the antilipotoxic effect mediated by Akt/FoxO1 signaling.
Department of Endocrinology, Chinese People's Liberation Army General Hospital, Beijing 100853, China.
Xiao-Jin
XJ
Li
Qing-Hua
QH
Guo
Xuan
X
Wang
Bing
B
Xue
Lian-Qing
LQ
Sun
Qu-Tao
QT
Meng
Ju-Ming
JM
Lu
Yi-Ming
YM
Mu
D000818:Animals; D017209:Apoptosis / Q000187:drug effects*; D015153:Blotting, Western; D045744:Cell Line, Tumor; D005227:Fatty Acids / Q000494:pharmacology*; D000071161:Forkhead Box Protein O1; D051858:Forkhead Transcription Factors / Q000235:genetics / Q000378:metabolism*; D051379:Mice; D009363:Neoplasm Proteins / Q000235:genetics / Q000378:metabolism*; D010766:Phosphorylation / Q000187:drug effects; D051057:Proto-Oncogene Proteins c-akt / Q000235:genetics / Q000378:metabolism*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D015398:Signal Transduction / Q000187:drug effects / Q000235:genetics
D005227:Fatty Acids; D000071161:Forkhead Box Protein O1; D051858:Forkhead Transcription Factors; C467200:Foxo1 protein, mouse; D009363:Neoplasm Proteins; D051057:Proto-Oncogene Proteins c-akt