The Resorcylic Acid Lactone Hypothemycin Selectively Inhibits theMitogen-Activated Protein Kinase Kinase-ExtracellularSignal-Regulated Kinase Pathway in Cells

摘要

The resorcylic acid lactone hypothemycin has been shown to inactivate protein kinases by binding to a cys-teine conserved in 46 protein kinases, including mitogen-activated protein kinase kinase (MEK), extracellularsignal-regulated kinase (ERK) and platelet-derived growth factor receptor (PDGFR). We assessed the selectivityof hypothemycin in cellular contexts. Hypothemycin normalized the morphology and inhibited anchorage-inde-pendent growth of Ki-ras transformed normal rat kidney (NRK) cells with selectivity and potency comparable toor greater than that of the MEK inhibitor U0126. In Ki-ras-transformed and phorbol 12-myristate 13-acetate(PMA)-treated NRK cells, hypothemycin blocked ERK activation but showed a minimal effect on autophospho-rylation of protein kinase Dl (PKD1), another kinase containing the conserved cysteine. Hypothemycin potentlyinhibited PDGFR autophosphorylation and activation of the MEK-ERK pathway in platelet-derived growth fac-tor (PDGF)-treated NRK cells. However, the phosphoinositide-3-kinase (P13K) pathway was only modestly atten-uated. Hypothemycin also inhibited growth factor- and anchorage-independent growth of human cancer celllines with a constitutively active MEK-ERK pathway. Although hypothemycin has the potential to inactivate var-ious protein kinases, the results indicate that in intracellular environments, hypothemycin can inhibit the MEK-ERK axis with sufficient selectivity to normalize transformed phenotypes of cells dependent on this pathway.