Induction of osteopontin mRNA expression during activation of murine NK cells.

Osteopontin (OPN) is an extracellular phosphorylated glycoprotein expressed in bone, kidney, nervous tissue, bone marrow, and granulated metrial gland (GMG) cells in murine decidua. We recently demonstrated that GMG cells are differentiated natural killer (NK) lineage cells that share phenotypic, functional, and morphologic characteristics with adherent interleukin-2 (IL-2)-activated NK cells. We now show that conditions that induce resting splenic NK cells to develop into adherent, activated cells induce the expression of opn mRNA. Nonstimulated NK cells did not express opn mRNA detectable by Northern analysis. However, expression was evident by day 1-2 of culture of NK cells with IL-2, increased to high levels by day 4, and was maintained at high levels thereafter. Thus, expression of mRNA for OPN, a secreted protein associated with cell adhesion, embryonic development, tissue remodeling, and immune regulation, is up-regulated during the activation of NK cells.