Expression pattern of osteopontin splice variants and its functions on cell apoptosis and invasion in glioma cells

Osteopontin (OPN) is widely overexpressed in various cancers, including gliomas, and plays an important role in tumorigenesis. However, the expression pattern and functions of OPN splice variants expressed in gliomas remain unclear. The aims of our current study were to examine the expression pattern and functions of OPN splice variants in gliomas. In present study, the mRNA levels of OPN splice variants are markedly increased in gliomas tissues, and all OPN splice variants were also found in U251 and U87 cells. Furthermore, knock-down and regain of function experiments were designed to explore the functions of OPN splice variants in U251 and U87 cells. Lentiviral vectors of OPN small interference RNA (siRNA) targeting all three endogenous mRNAs of OPN and OPN splice variants synonymous mutant that were not silenced by OPN siRNA were constructed. Our results showed that all OPN splice variants synonymous mutant-protected glioma cells from apoptosis induced by OPN siRNA through alteration of the levels of Bcl-2 family proteins and OPN-b Mu elicted a significant effect. Both OPN-a Mu and -c Mu promoted glioma cell invasion through alteration of the levels of uPA, MMP-2, and MMP-9 expressions and the activities of MMP-2 and MMP-9 via activation PI-3K/AKT/NF-kappaB signaling pathway. Moreover, OPN-c Mu showed the strongest effect on glioma cell invasion, while OPN-b Mu showed no effect on the invasion of U251 and U87 cells. Thus, different splice variants of OPN have divergent functions in regulating apoptosis and invasion of glioma cells, which broadens their importance in glioma biotherapy.