REGULATION OF THE PHOSPHORYLATION OF HUMAN PHARYNGEAL CELL-PROTEINS BY GROUP-A STREPTOCOCCAL SURFACE DEHYDROGENASE - SIGNAL-TRANSDUCTION BETWEEN STREPTOCOCCI AND PHARYNGEAL CELLS

Whether cell-to-cell communication results when group A streptococci i nteract with their target cells is unknown. Here, we report that upon contact with cultured human pharyngeal cells, both whole streptococci and purified streptococcal surface dehydrogenase (SDH) activate pharyn geal cell protein tyrosine: kinase as well as protein kinase C, thus r egulating the phosphorylation of cellular proteins. SDH, a major surfa ce protein of group A streptococci, has both glyceraldehyde-3-phosphat e dehydrogenase and ADP-ribosylating enzyme activities that may relate to early stages of streptococcal infection. Intact streptococci and p urified SDH induce a similar protein phosphorylation pattern with the de novo tyrosine phosphorylation of a 17-kD protein found in the membr ane/particulate fraction of the pharyngeal cells. However, this phosph olylation required the presence of cytosolic components. NH2-terminal amino acid sequence analysis identified the 17-kD protein as nuclear c ore histone H3. Both phosphotyrosine and phosphoserine-specific monocl onal antibodies reacted with the 17-kD protein by Western blot, sugges ting that the binding of SDH to these pharyngeal cells elicits a novel signaling pathway that ultimately leads to activation of histone H3-s pecific kinases. Genistein-inhibitable phosphorylation of histone H3 i ndicates that tyrosine kinase plays a key role in this event. Treatmen t of pharyngeal cells with protein kinase inhibitors such as genistein and staurosporine significantly inhibited streptococcal invasion of p haryngeal cells. Therefore, these data indicated that streptococci/SDH -mediated phosphorylation plays a critical role in bacterial entry int o the host cell. To identify the membrane receptor that elicits these signaling events, we found that SDH bound specifically to 30- and 32-k D membrane proteins in a direct ligand-binding assay. These findings c learly suggest that SDH plays an important role in cellular communicat ion between streptococci and pharyngeal cells that may be important in host cell gene transcription, and hence in the pathogenesis of strept ococcal infection.