Further studies on the enhancing factor and its possible mechanism of action

Abstract

In this study the nature of binding of enhancing factor (EF) and its mode of action are examined. EF binds to A431 cells through its own receptor, which is distinct from the receptor for epidermal growth factor (EGF). EF binds to the cell membrane and in turn provides a binding site for EGF. Data analyzed from Scatchard plots show that prior treatment of formalin-fixed A431 cells with EF for 30 minutes results in an increase in the number of binding sites for 125I-EGF. 3H-Thymidine incorporation studies, using the EGF-receptorless cell line NR-6, indicate that neither EF nor EGF alone stimulates the cells to synthesise DNA, but when both are added together the cells show 3H-thymidine incorporation. The role of EF may be to trap EGF and make it available to the cells through its own receptors even in the absence of EGF receptors. EF also induces anchorage-independent growth of normal fibroblasts in soft agar only in the presence of EGF.

Enhancing activity and phospholipase A2 activity: two independent activities present in the enhancing factor molecule

“…EF is a 14 kDa molecule isolated from mouse small intestines, identified by its ability to increase the binding of "#&I-EGF to A431 cells in the radio-receptor assay [1,2]. In the presence of EGF, EF stimulates DNA synthesis in itro in NR6 cells (cells devoid of functional EGF receptors) as well as inducing anchorage-independent growth in normal rat fibroblasts [2].…”

“…In the presence of EGF, EF stimulates DNA synthesis in itro in NR6 cells (cells devoid of functional EGF receptors) as well as inducing anchorage-independent growth in normal rat fibroblasts [2]. Therefore, we have proposed that EF gives the cell a growth advantage by making EGF available to it.…”

“…Therefore, we have proposed that EF gives the cell a growth advantage by making EGF available to it. To explain the increased binding, we had proposed that EF binds to its own cellsurface receptor and in turn offers a binding site for EGF [2].…”

“…EF increases the binding of epidermal growth factor (EGF) to A431 cells in the radio-receptor assay [1][2][3]. It was proposed that EF binds to a 100 kDa receptor on the cell surface, traps EGF and makes it available to the cell, thereby giving it a growth advantage [2].…”

“…EF increases the binding of epidermal growth factor (EGF) to A431 cells in the radio-receptor assay [1][2][3]. It was proposed that EF binds to a 100 kDa receptor on the cell surface, traps EGF and makes it available to the cell, thereby giving it a growth advantage [2]. Immunohistochemical studies have demonstrated that EF is localized predominantly in the Paneth cells of small intestine [4][5][6] and has been used as a marker for Paneth cells [7].…”