An altered IGF-I receptor is present in human leukemic cells

Area of Science:

• Endocrinology
• Molecular Biology
• Cancer Research

Background:

• The human leukemic cell line HL-60 is a model for studying cell proliferation.
• Insulin-like Growth Factor-I (IGF-I) and insulin play roles in cell growth and metabolism.
• Receptor tyrosine kinases are crucial in cell signaling pathways.

Purpose of the Study:

• To characterize IGF-I and insulin signaling in HL-60 cells.
• To investigate IGF-I receptor binding and autophosphorylation.
• To determine the molecular identity of the IGF-I/insulin receptor in HL-60 cells.

Main Methods:

• Cell growth assays at varying IGF-I and insulin concentrations.
• Radioligand binding studies using 125I-IGF-I.
• Chemical cross-linking and Western blotting to identify receptor subunits.
• Autophosphorylation analysis and peptide mapping.
• Enzymatic deglycosylation experiments.

Main Results:

• IGF-I stimulated cell growth at low concentrations (5 ng/ml); insulin required high concentrations (500 ng/ml).
• 125I-IGF-I binding indicated specific IGF-I receptor interactions with a 145-kDa protein.
• Both IGF-I and insulin induced autophosphorylation of a 105-kDa protein (pp105), not the typical 95-kDa beta-subunit.
• pp105 phosphorylation followed IGF-I receptor kinetics and showed distinct phosphorylation patterns compared to the insulin receptor beta-subunit.
• pp105 is likely a higher molecular weight beta-subunit of an IGF-I receptor variant.

Conclusions:

• HL-60 cells express a variant IGF-I receptor, possibly a fetal form.
• This re-expressed fetal IGF-I receptor may contribute to the malignant growth characteristics of HL-60 cells.
• The findings provide insights into receptor heterogeneity in leukemia.