Toxicon, Vol. 25, No. 6, pp. 637-647,1987. Printed in Great Britain. 0041-0101187 $3.00+ .00 Pergamon Journals Ltd. - STAPHYLOCOCCUS AUREUS a-TOXIN. 2. REDUCTION OF EPIDERMAL GROWTH FACTOR RECEPTOR AFFINITY IN PCl2 CELLS PHILIP LAZAROVICI1 and KAI-FoON lESSE CHAN' ISection on Growth Factors, National Institute of Child Health and Development, and 'Neurotoxicology Section, Laboratory of Experimental Neuropathology, National Institute of Neurological, Communicative Disorders and Stroke, National Institutes of Health, Bethesda, Maryland 20892, U.S.A. (Accepted for publication 31 December 1986) P. LAZAROVICI and K. -F. J. CHAN. Staphylococcus aureus a-toxin. 2. Reduction of epidermal growth factor receptor affinity in PC12 cells. Toxicon 25, 637 - 647 1987.-Staphylococcus aureus a-toxin, at sub-cytotoxic concentrations, inhibits both the 125I-labeledepidermal growth factor (EGF) binding and autophosphorylation properties of EGF-receptors in PC12 cells. This inhibition occurred only in intact cells and is probably due to a decrease in the affinity of the receptor for EGF. Streptolysin Sand parcelsin could mimic the a-toxin effect below cytotoxic concentrations, as measured by a 51Cr release assay. In contrast, other membrane perturbing toxins with different lipid specificity, such as tetanolysin and cobra direct lytic factor, inhibited [l"I]EGF binding only at cytotoxic concentrations. Staphylococcal a-toxin also stimulated 3-fold the specifiC' binding of a radioactive tumor-promoting phorbol ester (PDBu) to PC12 cells at concentrations similar to those required for the inhibition of [I"I]EGF binding. Although the exact mechanism for the inhibition of EGF binding by a-toxin has not been established, our results suggest that protein kinase C may be involved in this time-dependent process. INTRODUCTION PATHOGENICstaphylococci commonly produce purulent infection in humans. During the infection, a series of exotoxins are released into the interstitial tissue fluid which can induce histopathological effects, presumably by perturbations of specific membrane functions in target tissues (ALOUF, 1977). Among these exotoxins, Staphylococcus aureus a-toxin has been intensively investigated (HARSHMAN, 1979). This toxin can cause disruption of myelin sheaths in both central and peripheral nervous systems (HARSHMAN et al., 1985), probably due to stimulation of phosphorylation of some proteins, such as myelin basic protein in myelin, by specific protein kinase(s) (CHAN and LAZAROVICI, 1987). However, molecular studies related to other pathological effects are yet not available. Growth and proliferation of eukaryotic cells are under complex regulation. Some of these biological processes are controlled by a diverse group of mitogenic polypeptides termed growth factors (lAMESand BRADSHAW,1984). Epidermal growth factor (EGF) (CARPENTER and COHEN, 1979), for example, acts by binding to a specific transmembrane glycoprotein receptor (CARPENTER, 1984) which contains intrinsic tyrosine-specific protein kinase activity in the cytoplasmic domain (HUNTERand COOPER, 1981). EGF receptors have been found in rat pheochromocytoma (PC12) cells, which frequently serve as models for neuronal differentiation (GUROFF, 1985; LAZAROVICI et al., 1987). To determine the relationship between membrane integrity in cells of neuronal 637 .