Insulin-like growth factor expression in human cancer cell lines

Area of Science:

• Molecular Biology
• Cancer Research
• Endocrinology

Background:

• Insulin-like growth factors (IGFs), specifically IGF-I and IGF-II, are recognized as potent mitogens for various epithelial cancer cell lines.
• Previous research suggests that IGF-related ligands may function as autocrine growth factors for numerous cancer cell lines, acting through the type I IGF receptor (IGF-R).

Purpose of the Study:

• To investigate the expression and secretion of IGF-I and IGF-II in human lung and breast cancer cell lines.
• To determine the predominant IGF involved in the autocrine growth stimulation of these epithelial tumor cell lines.

Main Methods:

• Analysis of IGF-I, IGF-II, and IGF-R mRNA expression using reverse transcription of mRNA and polymerase chain reaction (RT-PCR).
• Detection and characterization of secreted IGF peptides in conditioned media from cancer cell lines grown in serum/hormone-free medium.
• Isolation and NH2-terminal sequencing of secreted IGF peptides using Western blotting under acidic conditions.

Main Results:

• IGF-I and IGF-II mRNAs were co-expressed with IGF-R in the majority of tested lung and breast cancer cell lines.
• Secreted IGF immunoreactivity, identified as differentially processed forms of IGF-II prohormone, was detected in three cell lines (two lung, one breast).
• Only one lung cancer cell line unequivocally secreted IGF-I peptide, despite high IGF-I gene expression.

Conclusions:

• Insulin-like growth factor-II (IGF-II) is the predominant IGF secreted by human lung and breast epithelial tumor cell lines.
• IGF-II actively participates in the autocrine growth stimulation of these cancer cells.
• The findings support the role of IGF-II/IGF-R autocrine loops as a common mechanism in epithelial carcinogenesis.