Ovarian Thecal/Interstitial Cells Produce an Epidermal Growth Factor-Like Substance*

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Abstract
An ovarian thecal/interstitial cell preparation was obtained by enzymatic digestion of immature rat ovaries depleted of granulosa cells. A component in thecal/interstitial cell-conditioned medium inhibited specific binding of [125I]iodoepidermal growth factor ([125I]EGF) to its cell surface receptor, as determined with an EGF radioreceptor assay. Thecal/interstitial cell secreted proteins also stimulated growth of an EGF-dependent cell line. Granulosa cells isolated from the same ovaries did not produce detectable levels of an EGF-like substance, as determined by both EGF RRA and EGF growth assay. Fractionation of thecal/interstitial cell secreted proteins by size exclusion HPLC resulted in a 35K component being detected by both the EGF RRA and the growth assay. An EGF-like substance was also detected when thecal/interstitial cell secreted proteins were fractionated by reverse phase HPLC. Several biochemical properties of the EGF-like substance examined were different from those of authentic mouse EGF. However, the biological activities of the EGF-like substance and mouse EGF were similar in their ability to promote the growth of an EGF-dependent cell line. In addition to the production of an EGF-like substance, the thecal/interstitial cell preparation also produced an EGF inhibitory activity. This thecal/interstitial cell secreted product was fractionated from the EGF-like substance and inhibited the ability of EGF to stimulate cell growth. EGF receptors are present on granulosa cells, and EGF is known to influence both the growth and differentiation of these cells. Observations indicate that ovarian thecal/interstitial cells produce an EGF-like substance that may act as a paracrine factor to regulate granulosa cell growth and differentiation. In addition, an EGF inhibitory activity is produced that also may have a role in regulating follicular cell growth.