Overexpression of the insulin-like growth factor I receptor in human colon carcinomas.
BACKGROUND
High concentrations of insulin-like growth factor (IGF)-I and IGF-II have been demonstrated in human colonic adenocarcinomas and exert mitogenic effects through paracrine/autocrine interactions with the IGF-I receptor (IGF-IR). However, definitive studies of IGF-IR expression in these tissues have not been performed.


METHODS
To study changes in the levels of the IGF-IR in colorectal carcinoma, we analyzed the expression of IGF-IR in 40 paired samples of normal and carcinomatous colonic tissue by quantitative reverse-transcription-polymerase chain reaction (RT-PCR), immunohistochemistry, and ligand binding.


RESULTS
As measured by RT-PCR, the IGF-IR mRNA ratio in paired tumor and adjacent normal mucosa was higher than 2.0 in 32 of 40 (80%) samples. The overall mean IGF-IR mRNA level was five-fold higher in tumor versus adjacent normal mucosa (P < 0.0001). Overexpression of IGF-IR in colon carcinomas was confirmed at the protein level by immunohistochemistry and receptor-binding studies. Colon carcinoma cells exhibited a positive staining for IGF-IR in 91% of all tumors (30 of 33) whereas the adjacent normal colonic epithelial cells showed only a very faint or no significant IGF-IR immunoreactivity. Radioligand assays and Scatchard analysis in both tissue types revealed a single class of high-affinity IGF-IR-binding sites with a similar dissociation constant (K(d;) 0.14 +/- 0.02 nmol/L, n = 18). However, specific (125)IGF-I-binding and receptor concentrations were elevated in tumor membranes compared with normal mucosa (33.6 +/- 5.6 vs. 22.7 +/- 3.4 fmol/mg protein, P < 0.05). IGF-I affinity crosslinking and sodium dodecyl sulfate-polyacrylamide gel electrophoresis displayed specific bands corresponding to the size of the normal alpha-subunit of the IGF-IR that were more intense in carcinomatous samples. IGF-II mRNA levels were significantly elevated in colorectal carcinomas (P < 0.0001). The IGF-II mRNA ratio in tumor versus normal tissue was elevated more than twofold in 28 of 40 paired samples and a positive correlation was observed between the overexpression of IGF-II and IGF-IR in the tumors.


CONCLUSIONS
Our results demonstrate that, in addition to IGF-II, a strong overexpression of IGF-IR is found in the majority of colorectal carcinomas, supporting the hypothesis of an important role of the IGF system in the pathogenesis of colorectal carcinoma.
Weber
Matthias M
MM
Klinik II und Poliklinik für Innere Medizin der Universität zu Köln und Lehrstuhl II für Innere Medizin, Köln, Germany. MMWeber@t-online.de
Fottner
Christian
C
Liu
Sun Bin
SB
Jung
M Christina
MC
Engelhardt
Dieter
D
Baretton
Gustavo B
GB
D000230:Adenocarcinoma / Q000378:metabolism*; D015179:Colorectal Neoplasms / Q000378:metabolism*; D005260:Female; D015870:Gene Expression; D015972:Gene Expression Regulation, Neoplastic; D006801:Humans; D007150:Immunohistochemistry; D008297:Male; D008875:Middle Aged; D012333:RNA, Messenger / Q000032:analysis / Q000378:metabolism*; D017526:Receptor, IGF Type 1 / Q000235:genetics / Q000378:metabolism*; D020133:Reverse Transcriptase Polymerase Chain Reaction
D012333:RNA, Messenger; D017526:Receptor, IGF Type 1