Background
Gastric adenocarcinoma is common and consequent mortality high. Presentation and mortality are increased in obese individuals, many of whom have elevated circulating insulin concentrations. High plasma insulin concentrations may promote, and increase mortality from, gastric adenocarcinoma. Tumour promotion activities of insulin and its receptor are untested in gastric cancer cells.
Conclusions
The insulin and IGF signal transduction pathway is dominant in gastric adenocarcinoma. Gastric adenocarcinoma cell survival depends upon insulin receptor. That insulin has direct cancer-promoting effects on tumour cells has implications for clinical management of obese and diabetic cancer patients.
Methods
Tumour gene amplification and expression were computed from sequencing and microarray data. Associations with patient survival were assessed. Insulin-dependent signal transduction, growth, apoptosis and anoikis were analysed in metastatic cells from gastric adenocarcinoma patients and in cell lines. Receptor involvement was tested by pharmacological inhibition and genetic knockdown. RNA was analysed by RT-PCR and proteins by western transfer and immunofluorescence.
Results
INSR expression was higher in tumour than in normal gastric tissue. High tumour expression was associated with worse patient survival. Insulin receptor was detected readily in metastatic gastric adenocarcinoma cells and cell lines. Isoforms B and A were expressed. Pharmacological inhibition prevented cell growth and division, and induced caspase-dependent cell death. Rare tumour INS expression indicated tumours would be responsive to pancreatic or therapeutic insulins. Insulin stimulated gastric adenocarcinoma cell PI3-kinase/Akt signal transduction, proliferation, and survival. Insulin receptor knockdown inhibited proliferation and induced programmed cell death. Type I IGF receptor knockdown did not induce cell death. Conclusions: The insulin and IGF signal transduction pathway is dominant in gastric adenocarcinoma. Gastric adenocarcinoma cell survival depends upon insulin receptor. That insulin has direct cancer-promoting effects on tumour cells has implications for clinical management of obese and diabetic cancer patients.