Actions of IGF-I are differentially regulated by fatty acids in normal and breast cancer epithelial cells

Introduction

Obesity will soon be the leading preventable risk factor for many cancers. The insulin-like growth factors (IGFs) have been strongly implicated as important risk factors for many epithelial cancers, including breast cancer, and for mediating the link between nutrition and these cancers. Obesity-related increases in circulating fatty acids cause insulin resistance with consequent morbidity but, despite the considerable overlap between insulin and IGFs, there have been no studies of the effects of fatty acids on IGF activity.

Objective

To examine the effects of the most abundant circulating fatty acids (oleate – unsaturated; palmitate – saturated) alone and in combination with IGF-I on MCF-10A nonmalignant breast and MCF-7 breast cancer epithelial cells.

Methods

Following 24 hours in serum-free media, cells were exposed to albumin-bound fatty acids (100 to 400 μM) for 48 hours with or without IGF-I (20 to 25 ng/ml). Cell growth and death were assessed by cell counting and the trypan blue dye exclusion assay, respectively. Data were analysed by ANOVA.

Results

For MCF10-A and MCF-7 cells, IGF-I increased cell growth (P < 0.01 and P < 0.001) whereas oleate (100 to 400 μM) alone had no effect. However, IGF-induced growth was differentially affected in combination with oleate: being enhanced in the MCF-10A cells (by 57% at 400 μM; P < 0.001) but inhibited in the cancer cells (by 28% at 400 μM; P < 0.05).

For both cell lines, palmitate alone only inhibited growth at the highest dose (400 μM), which was coincident with the induction of apoptosis. Palmitate did not affect IGF-induced proliferation in either cell line. The cells were differentially sensitive to palmitate-induced death (at 400 μM a 1.5-fold increase of MCF-7 cells; an eightfold increase of MCF-10A cells). Palmitate-induced death in MCF10-A cells was inhibited by a ceramide synthase inhibitor, fumonisin B1 (0.1 μM) (61%), and by oleate (96% at 400 μM) but was unaffected in the presence of IGF-I.

We are currently investigating the signalling pathways underlying the differential effects of oleate on IGF-induced growth of MCF-10A and MCF-7 cells.

Conclusion

Palmitate had no effect on IGF-induced cell growth, whereas oleate enhanced that of normal cells but inhibited that of cancer cells. Unlike oleate, palmitate induced apoptosis although cancer cells were relatively resistant to this. This apoptosis was via ceramide production and was inhibited by oleate but not IGF-I. Saturated and unsaturated fatty acids have differential effects on IGF-induced growth and the survival of human breast epithelial cells, supporting the notion that nutrition is a major environmental influence on breast cancer progression.