TNF and central nervous system cancer: To determine whether the Tat-induced P2Y4R pathway also works in human astrocyte, human glioma U251 cells were pretreated with or without PD98059 and LY294002 for 2 h, followed by soluble Tat stimulus for another 6 h, and PRY4R protein expression was then determined by immunoblot assay; the mRNA levels of TNFα, IL-6, MCP-1, and ATP were detected by qPCR and ATPlite luminescence assay, respectively.