TNF and osteosarcoma: 1999). For example, Kumar and coworkers showed a dose-dependent increase in p38 phosphorylation with SB203580 in a number of cell lines including human monocytic THP-1 cells, osteosarcoma MG63 and chondrocyte C20A4 cells (Kumar et al. 1999). Thus, the functional significance of phosphorylation of p38 MAPK at T180/Y182 is unclear. Importantly, however, using RNAi to knockdown p38 MAPK expression, we provide conclusive evidence that p38 MAPK mediates the effects of TNF-α on trophoblast amino acid transport.