Uterine leiomyomas (fibroids) are the most common benign tumors in women. Recently, three populations of leiomyoma cells were discovered on the basis of CD34 and CD49b expression, but molecular differences between these populations remain unknown.

To define differential gene expression and signaling pathways in leiomyoma cell populations.

Cells from human leiomyoma tissue were sorted by flow cytometry into three populations: CD34⁺/CD49b⁺, CD34⁺/CD49b⁻, and CD34⁻/CD49b⁻. Microarray gene expression profiling and pathway analysis were performed. To investigate the insulinlike growth factor (IGF) pathway, real-time quantitative polymerase chain reaction, immunoblotting, and 5-ethynyl-2′-deoxyuridine incorporation studies were performed in cells isolated from fresh leiomyoma.

Research laboratory.

Eight African American women.

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Gene expression patterns, cell proliferation, and differentiation.

A total of 1164 genes were differentially expressed in the three leiomyoma cell populations, suggesting a hierarchical differentiation order whereby CD34⁺/CD49b⁺ stem cells differentiate to CD34⁺/CD49b⁻ intermediary cells, which then terminally differentiate to CD34⁻/CD49b⁻ cells. Pathway analysis revealed differential expression of several IGF signaling pathway genes. IGF2 was overexpressed in CD34⁺/CD49b⁻ vs CD34⁻/CD49b⁻ cells (83-fold; P < 0.05). Insulin receptor A (IR-A) expression was higher and IGF1 receptor lower in CD34⁺/CD49b⁺ vs CD34⁻/CD49b⁻ cells (15-fold and 0.35-fold, respectively; P < 0.05). IGF2 significantly increased cell number (1.4-fold; P < 0.001), proliferation indices, and extracellular signal-regulated kinase (ERK) phosphorylation. ERK inhibition decreased IGF2-stimulated cell proliferation.

IGF2 and IR-A are important for leiomyoma stem cell proliferation and may represent paracrine signaling between leiomyoma cell types. Therapies targeting the IGF pathway should be investigated for both treatment and prevention of leiomyomas.