A preliminary report on an integrin-like protein in protoplasts of the entomopathogenic fungus Entomophaga aulicae

Abstract

Integrins are transmembrane proteins involved in cell adhesion and signal transduction. This study reports findings on a possible integrin-like protein in an entomopathogenic fungus, Entomophaga aulicae. -- Extracts of Entomophaga aulicae protoplasts contained a 71 kDa protein which cross-reacted with antiserum raised against a β₁-chicken-integrin. The inclusion of DTT in the cell extracts had no effect on the mobility of this protein indicating the lack of a significant number of sulfur-sulfur bonds. A combination of eight protease inhibitors was necessary to prevent protein degradation in order to obtain consistent results. Positive and negative controls supported these results. -- Using immunofluorescence microscopy, similar patterns of abundant peripheral patches of staining were detected at the periphery of the protoplast when probed with four different anti-integrin or anti-β-integrin like protein antibodies. Controls showed that staining of the periphery of the nucleus and staining of the nuclear "core" were non-specific. This conclusion is tentative however since we were unable to show characteristic integrin staining in positive controls of monkey kidney fibroblasts. -- In cell adhesion assays, there was no evidence to support the hypothesis that E. aulicae protoplasts attach to either a host insect cell line, or to the integrin-binding proteins, fibronectin and collagen. Future experiments using newly isolated protoplasts and cell lines derived from insect fat body may be more instructive. -- We conclude that while we have preliminary evidence for an integrin-like protein in E. aulicae, strong support for integrin in any fungus remains elusive.