Streptococcus Mutans GS-5 Antigen I/II Stimulates Cell Survival in Serum Deprived-Cultures Through PI3K/Akt Pathways Young-Ok Son, 1 Young-Mi Jeon, 2 Yu-Shin Kim, 2 Soon-Sun Park, 2 Seung-Moon Park, 3 Ji-Hae Kim, 2 and Jeong-Chae Lee 1,2 * 1 Graduate Center for Toxicology, University of Kentucky, Lexington, Kentucky 40536-0001 2 Institute of Oral Biosciences and BK21 Program, School of Dentistry, Chonbuk National University, Jeonju 561-756, South Korea 3 Division of Biotechnology, Chonbuk National University, Iksan 570-752, South Korea ABSTRACT The antigen I/II (AgI/II) protein is a major surface protein that mediates the attachment of Streptococcus mutans (S. mutans) to the saliva- coated pellicle. Numerous studies have investigated not only the mechanisms by which AgI/II signaling is transduced within cells, but have also attempted to use AgI/II-specific antibodies to treat dental caries and host immune responses. However, little information is available about the effects of AgI/II on basic cellular events in bone cells. In this study, we examined the effects of the His-tagged recombinant N- terminal half of the AgI/II protein (rAgI/II-N) generated from S. mutans GS-5 on the viability, proliferation, and cell cycle progression of primary calvarial osteoblasts. We also investigated the mechanisms involved in the rAgI/II-N-mediated survival of serum-starved osteoblasts. We found that rAgI/II treatment attenuated the serum deprivation-induced decrease in cell viability and proliferation of osteoblasts. rAgI/II-N also prevented the loss of mitochondrial membrane potential (MMP), alterations in levels of two key mitochondrial Bcl-2 family proteins, and the accumulation of numerous cells into the sub-G 1 phase that were observed in serum-starved osteoblasts. Pharmacological inhibitors of phosphoinositide 3-kinase (PI3K), but not of extracellular signal-regulated kinase or Ras, blocked the rAgI/II-N-mediated protection against serum deprivation-induced cell death. Additional experiments revealed that the integrin a5b1-mediated PI3K pathway is required for rAgI/II- N-mediated Akt phosphorylation in osteoblasts. Collectively, these results suggest that rAgI/II-N induces survival signals in serum-starved osteoblasts through integrin-induced PI3K/Akt signaling pathways. J. Cell. Biochem. 113: 1724–1732, 2012. ß 2011 Wiley Periodicals, Inc. KEY WORDS: RECOMBINANT AgI/II; CALVARIAL OSTEOBLASTS; SURVIVAL; CELL CYCLE PROGRESSION; SIGNAL TRANSDUCTION PATHWAYS S treptococcus mutans (S. mutans) is known as the most important mediator of dental caries [Loesche, 1986]. Many investigators have focused their efforts on developing vaccines or passive immunization protocols that are capable of preventing S. mutans-mediated diseases [Kitten et al., 2002; Han et al., 2006]. The results of numerous studies suggest that vaccination using peptides derived from a surface protein of S. mutans, antigen I/II (AgI/II), is a very promising strategy for controlling and preventing dental caries [Robinette et al., 2011]. Because the role of AgI/II in host responses is important, many studies have explored the mechanisms by which the AgI/II signal is transduced within cells. AgI/II is known to bind directly to dentinal cell surface receptors such as a5b1 integrins and Toll-like receptor 4 [Hajishengallis et al., 2002]. This binding induces the expression of surface molecules required for adhesion and migration of cells [Heddle et al., 2003; Nobbs et al., 2007]. Especially, integrins are known to play important roles in transducing extracellular stimulation into cellular signals and thereby affecting cellular events such as proliferation, differentiation, and apoptosis. Li et al. [2011] demonstrated the contribution of integrin-mediated signal- ing in the promotion of cell survival and cell cycle progression. It was also reported that the activation of integrin-linked kinase Journal of Cellular Biochemistry ARTICLE Journal of Cellular Biochemistry 113:1724–1732 (2012) 1724 Young-Ok Son and Young-Mi Jeon contributed equally to this work. Additional Supporting Information may be found in the online version of this article. *Correspondence to: Prof. Jeong-Chae Lee, Institute of Oral Biosciences (BK21 program) and School of Dentistry, Research Center of Bioactive Materials, Chonbuk National University, Jeonju 561-756, South Korea. E-mail: leejc88@jbnu.ac.kr Received 21 September 2011; Accepted 21 December 2011  DOI 10.1002/jcb.24042  ß 2011 Wiley Periodicals, Inc. Published online 28 December 2011 in Wiley Online Library (wileyonlinelibrary.com).