Epstein-Barr virus LMP2A transforms epithelial cells, inhibits cell differentiation, and activates Akt

The Epstein-Barr virus LMP2A protein was expressed in a human keratinocyte cell line, HaCaT, and effects on epithelial cell growth were detected in or ganotypic raft cultures and in vivo in nude mice. Raft cultures derived fro m LMP2A-expressing cells were hyperproliferative, and epithelial differenti ation was inhibited. The LMP2A-expressing HaCaT cells were able to grow anc horage independently and formed colonies in soft agar. HaCaT cells expressi ng LMP2A were highly tumorigenic and formed aggressive tumors in nude mice. The LMP2A tumors were poorly differentiated and highly proliferative, in c ontrast to occasional tumors that arose from parental HaCaT cells and vecto r control cells, which grew slowly and remained highly differentiated. Anim als injected with LMP2A-expressing cells developed frequent metastases, whi ch predominantly involved lymphoid organs. Involucrin, a marker of epitheli al differentiation, and E-cadherin, involved in the maintenance of intercel lular contact, were downregulated in LMP2A tumors. Whereas activation of th e mitogen-activated protein kinase pathway was not observed, phosphatidylin ositol 3-kinase (PI3-kinase)-dependent activation of the serine-threonine k inase Akt was detected in LMP2A-expressing cells and LMP2A tumors. Inhibiti on of this pathway blocked growth in soft agar. These data indicate that LM P2A greatly affects cell growth and differentiation pathways in epithelial cells, in part through activation of the PI3-kinase-Akt pathway.