Messenger ribonucleic acid expression of the insulin-like growth factors and their binding proteins in uterine fibroids and myometrium

Fibroids (leiomyomata) are the most common tumors in women, but their etiology is unknown. The insulin-like growth factors (IGFs) and their binding proteins (IGFBPs) may be important in the growth of these benign neoplasms. We have examined the presence of mRNA encoding both IGF-I and IGF-II and IGFBP-1, -2, and -3 in fibroids and corresponding myometrium from 20 women undergoing hysterectomy for symptomatic uterine fibroids. Northern blots of total cellular RNA were probed with oligonucleotides for IGF-I, IGF-II, IGFBP-2, and IGFBP-3 and a human IGFBP-1 cDNA. Western ligand blotting was also used to detect the presence of IGFBP proteins in both fibroid and myometrium. The data showed that in fibroids compared to myometrium, 1) the relative abundance of IGF-I mRNA was not different, but there was an increase in the relative abundance of IGF-II mRNA (P < 0.001); 2) IGFBP-1 mRNA was undetectable in fibroids and detectable in only 1 specimen of myometrium; 3) there was no difference in the relative abundance of IGFBP-2 mRNA, but there was an increase in the relative abundance of IGFBP-3 mRNA in myometrium (P < 0.05). By Western ligand blotting, both IGFBP-2 and -3 proteins were present. Our data show that the mRNAs encoding IGF-I, IGF-II, IGFBP-2, and IGFBP-3 are expressed in both fibroids and myometrium and that fibroids express more IGF-II and less IGFBP-3 mRNA than myometrium. We postulate that the net effect of the changes seen is to increase the bioavailability of free (bioactive) IGF, which may then play a major role in promoting fibroid tumor growth.