Relationship Between Growth Activity And Expression Of Egf Receptor And Downstream Signalling Proteins In The Human Lens

Abstract

Abstract: : Purpose: The present study investigated the expression pattern of EGFR and the signalling components, PLCgamma and ERK and related this distribution to growth in the normal and wounded lens. Methods: Anterior and equatorial regions of the native epithelium were prepared separately from donor lenses and in vitro capsular bags were prepared and cultured. Receptor distribution was determined by immunocytochemistry and RT–PCR. Western blot analysis of PLCgamma and ERK (total and active) was carried out on cell lysates. Function was determined by calcium imaging of FURA–2 loaded cells and also, in the case of capsular bags, by cell growth. Results: Immunocytochemistry and RT–PCR showed an even distribution of EGFR across the native epithelium. Whole lenses, however, in response to 10ng/ml EGF only exhibit a calcium response at the equatorial region. Western blots demonstrated significantly greater expression of PLCgamma and ERK (total and active) in the equator relative to the central region. Addition of EGF increased growth rates of cells in capsular bags and an EGFR inhibitor decreased rates. EGF also induced a calcium response in posterior capsule cells of capsular bags. Conclusions: EGFR is evenly distributed across the entire epithelium, while related calcium signalling and expresssion of PLCgamma and ERK has a marked bias to the equator. Therefore, levels of downstream enzyme components rather than changes in receptor expression dictate EGFR signalling output in the normal lens. In the wounded lens (capsular bag) EGFR signalling persists in cells growing on the PC.

Keywords: growth factors/growth factor receptors • signal transduction • proliferation