DUAL LEUCINE ZIPPER-BEARING KINASE (DLK) ACTIVATES P46(SAPK) AND P38(MAPK) BUT NOT ERK2

Because the catalytic domain of dual leucine zipper-bearing kinase (DL K) bears sequence similarity to members of the mitogen-activated prote in (MAP) kinase kinase kinase subfamily, this protein kinase was inves tigated for its ability to activate MAP kinase pathways. When transien tly transfected and overexpressed in either COS 7 cells or NIH3T3 cell s, wild type DLK potently activated p46(SAPK) (SAPK/JNK) but had no de tectable effect in activating p42/44(MAPK). DLK also activated p38(map k) when overexpressed in NIH3T3 cells. A catalytically inactive point mutant of DLK had no effect in these experiments. Consistent with its specificity in activating SAPK, DLK activated Elk-1 but not Sapla-medi ated transcription. In NIH3T3 cells, activation of SAPK by v-Src was m arkedly attenuated by coexpression of K185A, a catalytically inactive mutant of DLK, suggesting that this mutant could function in a dominan t negative fashion in a pathway that leads from v-Src to SAPKs. In a s eries of co-transfection experiments, activation of p46(SAPK) by DLK w as not inhibited by dominant negative mutants of Rad and Cdc42Hs, PAK6 5-R, or PAK65-A, but was attenuated by MEKK1(K432M). DLK(K185A) did no t inhibit the ability of constitutively active MEKK1 to activate SAPK. Moreover, K185A significantly inhibited the activation of SAPK by con stitutively active V-12 Rad and V-12 Cdc42Hs. These results suggest th at DLK lies distal to Rac1 and/or Cdc42Hs but proximal to MEKK1 in a p athway leading from v-Src to SAPKs activation.