Gene expression of the insulin-like growth factors and their receptors in cultured human retinal pigment epithelial cells

Insulin-like growth factors I and II (IGF I and II) are polypeptides with both growth-promoting and insulin-like metabolic effects^16,27. Immunoreactive IGF I is present in the retina¹⁴ and both IGF I and II are present in vitreal fluid¹². The type I and type II IGF receptors are also localized within the neural retina^3,15,20,33. The presence of IGFs and IGF receptors within the eye suggests a possible growth-promoting effect of IGFs on ocular tissues. IGF may enter the eye from the blood or, alternatively, arise from an ocular cell type which synthesizes and secretes IGF. IGF I and II mRNA synthesis in scleral cells¹³ and IGF I synthesis in rat retina¹⁴ suggests endogenous IGF production in the eye. We hypothesized that IGFs and IGF receptors are synthesized by one ocular cell type, the retinal pigment-epithelium (RPE). As a first step in studying IGF production by the RPE, we analyzed expression of the IGF and IGF receptor genes by cultured human RPE cells. Using Northern analysis, RNase protection and reverse-transcriptase polymerase chain reaction (RT-PCR), we found that cultured RPE cells synthesize mRNA for IGF I and the type II IGF receptors.