Translationally controlled tumour protein (TCTP) is a novel glucose-regulated protein that is important for survival of pancreatic beta cells.
OBJECTIVE
This study used proteomics and biochemical approaches to identify novel glucose-regulated proteins and to unveil their role in pancreatic beta cell function. Translationally controlled tumour protein (TCTP) was identified to be one such protein, and further investigations into its function and regulation were carried out.


METHODS
Global protein profiling of beta cell homogenates following glucose stimulation was performed using two-dimensional gel electrophoresis. Proteins were identified by mass spectroscopy analysis. Immunoblotting was used to investigate alterations in TCTP protein levels in response to glucose stimulation or cell stress induced by palmitate. To investigate the biological function of TCTP, immunolocalisation, gene knockdown and overexpression of Tctp (also known as Tpt1) were performed. Apoptosis was measured in Tctp knockdown or Tctp-overexpressing cells. Glucose-stimulated insulin secretion was carried out in Tctp knockdown cells.


RESULTS
TCTP was identified as a novel glucose-regulated protein, the level of which is increased at stimulatory glucose concentration. Glucose also induced TCTP dephosphorylation and its partial translocation to the mitochondria and the nucleus. TCTP protein levels were downregulated in response to cell stress induced by palmitate or thapsigargin treatments. Gene knockdown by small interfering RNA led to increased apoptosis, whereas overproduction of TCTP prevented palmitate-induced cell death.


CONCLUSIONS
Regulation of TCTP protein levels by glucose is likely to be an important cyto-protective mechanism for pancreatic beta cells against damage caused by hyperglycaemia. In contrast, high concentration of palmitate causes cell stress, reduction in TCTP levels and consequently reduced cell viability. Our results imply that TCTP levels influence the sensitivity of beta cells to apoptosis.
Centre for Research in Biomedicine, Faculty of Health and Life Sciences, University of the West of England, Bristol BS16 1QY, UK.
F
F
Diraison
K
K
Hayward
K L
KL
Sanders
F
F
Brozzi
S
S
Lajus
J
J
Hancock
J E
JE
Francis
E
E
Ainscow
U A
UA
Bommer
E
E
Molnar
N D
ND
Avent
A
A
Varadi
D000818:Animals; D006801:Humans; D051379:Mice; D017209:Apoptosis / Q000187:drug effects; D014408:Biomarkers, Tumor / Q000235:genetics / Q000378:metabolism; D002460:Cell Line; D002470:Cell Survival / Q000187:drug effects / Q000235:genetics; D015180:Electrophoresis, Gel, Two-Dimensional; D018840:HSP70 Heat-Shock Proteins / Q000235:genetics / Q000378:metabolism; D020287:In Situ Nick-End Labeling; D050417:Insulin-Secreting Cells / Q000166:cytology / Q000378:metabolism; D007525:Isoelectric Focusing; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism; D010169:Palmitic Acids / Q000494:pharmacology; D020133:Reverse Transcriptase Polymerase Chain Reaction; D034741:RNA, Small Interfering; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization; D000090324:Tumor Protein, Translationally-Controlled 1
D014408:Biomarkers, Tumor; C018551:glucose-regulated proteins; D018840:HSP70 Heat-Shock Proteins; D008565:Membrane Proteins; D010169:Palmitic Acids; D034741:RNA, Small Interfering; C000715647:TPT1 protein, human; C000715648:Tpt1 protein, mouse; D000090324:Tumor Protein, Translationally-Controlled 1