Molecular mechanism of human-specific infection by an oral streptococcus, Streptococcusintermedius

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In order to clarify the human cell-specific infection depending on a cytolysin, intermedilysin (ILY) by an oral streptococcus Streptococcus intermedius (SI), the effects of ILY and SI cells on culture cells such as human hepatoma HepG2 were investigated. Because significant binding between SI cells and microvilli of human cell surface was found in TEM observation of SI-infected HepG2, some intracellular cytoskeletal network was suggested to participate in the start of SI invasion into human cells. Actually, it was revealed that intracellular actin network changed with proceeding of SI infection. It was confirmed that the phosphorylation level of a tyrosine kinase involved in regulation of cytoskeletal protein significantly increased(five-fold of basic level)by treatment of HepG2 with low level of ILY in phosphorylation analysis of a large number of signal transduction tyrosine kinases. So, this signal transduction protein was suggested to play a role in the human cell-specific SI infection depending on ILY. Moreover, host cell death induced by SI infection tended to decrease by the treatment with a PLA2 inhibitor, quinacrine. Further investigation is proceeding on the relationship among two signal transduction members and SI infection. Induction of LC3, a marker of autophagy, was also examined but remarkable increase of LC3 could not detect in HepG2 at the early stage of ST infection.Preparation of transgenic mice with huCD59 was carried out to investigate SI infection mechanism in vivo. A gene construct of huCD59 with mouse CD59a promoter was introduced into fertilized eggs of C57BL/6 mice and two transgenic mice were obtained after screening. Two+/+strains are preparing from these mice.