Downregulation of IGF-IR expression by RNAi inhibits proliferation and enhances chemosensitization of human colon cancer cells.
OBJECTIVE
Colon cancer is the second leading cause of cancer death worldwide. Elevated expression of insulin-like growth factor-I receptor (IGF-IR) is a frequent genetic abnormality seen in this malignancy. For a better understanding of its role in maintaining the malignant phenotype, we used RNA interference (RNAi) directed against IGF-IR in our study. The aim of this study was to examine the anti-proliferation and chemosensitization effects elicited by a decrease in the transcription and protein levels of IGF-IR by RNAi in SW480 colon cancer cells.


METHODS
A plasmid-based polymerase III promoter system was used to deliver and express short interfering RNA (siRNA) targeting IGF-IR to reduce its expression in SW480 cells. Western blot analysis was used to measure the protein level of IGF-IR. We assessed the effects of IGF-IR silencing on cancer cell growth by a cell growth curve. The effect of the 5-fluorouracil (5-FU)-induced cell death by knockdown of IGF-IR was also investigated by methyl thiazolyl tetrazolium assay.


RESULTS
Transfection of siRNA targeting IGF-IR was shown to reduce IGF-IR messenger RNA levels by 95%. Western blotting detected a similar inhibition of IGF-IR protein levels in those cells. The cells transfected with PKD-short hairpin RNA-IGF-IR-V2 significantly decreased cell growth and rendered cells more sensitive to chemotherapy. The highest proliferation inhibitory and chemosensitization ratios were 53 +/- 2% and 1.78, respectively.


CONCLUSIONS
This study indicates that downregulation of IGF-IR results in significant inhibition of tumor growth in vitro. It also provides a promising strategy to chemotherapy efficacy in human tumors and forming a basis for future in vivo trials.
Yavari
Kamal
K
Department of Clinical Biochemistry, Tarbiat Modares University, Tehran, Iran.
Taghikhani
Mohammad
M
Ghannadi Maragheh
Mohammad
M
Mesbah-Namin
Seyed A
SA
Babaei
Mohammad Hossein
MH
D045744:Cell Line, Tumor; D049109:Cell Proliferation / Q000187:drug effects; D003001:Cloning, Molecular; D003110:Colonic Neoplasms / Q000235:genetics / Q000378:metabolism* / Q000473:pathology*; D015536:Down-Regulation / Q000187:drug effects*; D004354:Drug Screening Assays, Antitumor; D005472:Fluorouracil / Q000494:pharmacology*; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects; D005822:Genetic Vectors / Q000235:genetics; D006801:Humans; D008856:Microscopy, Fluorescence; D010957:Plasmids / Q000235:genetics; D034622:RNA Interference / Q000187:drug effects*; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D017526:Receptor, IGF Type 1 / Q000378:metabolism*; D014170:Transformation, Genetic / Q000187:drug effects
D012333:RNA, Messenger; D017526:Receptor, IGF Type 1; D005472:Fluorouracil