Specific regulation of JNK signalling by the novel rat MKK7gamma1 isoform.
The c-Jun N-terminal kinases (JNKs) mediate a diversity of physiological and pathophysiological effects. Apart from isoform-specific JNK activation, upstream kinases are supposed to be the relevant regulators, which are involved in the context- and signalosome-depending functions. In the present study we report the cloning and characterization of the novel rat MKK7gamma1, a splice variant of MKK7 with an additional exon in the N-terminal region, in the neuronal pheochromocytoma cell line PC12. Transfected MKK7gamma1 increased basal JNK activity, in particular phosphorylation of JNK2. Consequently, JNK signalling was changed in mRNA-, protein- and activation-levels of JNK targets, such as transcription factors (c-Jun, p53, c-Myc), cell cycle regulators (p21, CyclinD1) and apoptotic proteins (Fas, Bim, Bcl-2, Bcl-xl). These alterations promote the sensitivity of MKK7gamma1-transfected cells towards cell death and repress cell proliferation under normal cell growth conditions. Complexes of JIP-1, MKK7 and JNK2 were the major JNK signalosomes under basal conditions. After stimulation with taxol (5muM) and tunicamycin (1.4mug/ml), MKK7gamma1- but not MKK7beta1-transfection, reduced cell death and even increased cell proliferation. Cellular stress also led to an increased phosphorylation of JNK1 and the almost complete abrogation of complexes of JIP-1, MKK7 and JNK2 in MKK7gamma1-transfected PC12 cells. Summarizing, MKK7gamma1 affects the function and activity of individual JNK isoforms and the formation of their signalosomes. This study demonstrates for the first time that one splice-variant of MKK7 tightly controls JNK signalling and effectively adapts JNK functions to the cellular context.
Haeusgen
Wiebke
W
Institute of Experimental and Clinical Pharmacology, University Hospital Schleswig-Holstein, Campus Kiel, Hospitalstrasse 4, 24105 Kiel, Germany.
Herdegen
Thomas
T
Waetzig
Vicki
V
D048868:Adaptor Proteins, Signal Transducing / Q000378:metabolism; D000595:Amino Acid Sequence; D000818:Animals; D000900:Anti-Bacterial Agents / Q000494:pharmacology; D000972:Antineoplastic Agents, Phytogenic / Q000494:pharmacology; D017209:Apoptosis; D045744:Cell Line, Tumor; D049109:Cell Proliferation; D048031:JNK Mitogen-Activated Protein Kinases / Q000378:metabolism*; D048688:MAP Kinase Kinase 7 / Q000378:metabolism*; D020935:MAP Kinase Signaling System; D008969:Molecular Sequence Data; D017239:Paclitaxel / Q000494:pharmacology; D010766:Phosphorylation; D020033:Protein Isoforms / Q000378:metabolism; D051381:Rats; D014415:Tunicamycin / Q000494:pharmacology; D015854:Up-Regulation
D048868:Adaptor Proteins, Signal Transducing; D000900:Anti-Bacterial Agents; D000972:Antineoplastic Agents, Phytogenic; C110528:Mapk8ip1 protein, rat; D020033:Protein Isoforms; D014415:Tunicamycin; D048031:JNK Mitogen-Activated Protein Kinases; D048688:MAP Kinase Kinase 7; D017239:Paclitaxel