title: Mixed lineage kinase 3 inhibits phorbol myristoyl acetate-induced DNA synthesis but not osteopontin expression in rat mesangial cells.
abstract: Mixed lineage kinase 3 (MLK 3) (also called SPRK or PTK-1) is a recently described member of the family of the mixed lineage kinase subfamily of Ser/Thr protein kinases that interacts with mitogen-activated protein kinase pathways. In order to test the biological relevance and potential interaction of MLK 3 with protein kinase C-mediated signaling pathways, human MLK 3 was stably expressed in rat glomerular mesangial cells using a retroviral vector (LXSN) and the effects of phorbol myristoyl acetate (PMA) on DNA synthesis and osteopontin mRNA expression were examined. In control (vector-transfected) mesangial cells PMA increased [3H]-thymidine incorporation in a concentration-dependent manner. In mesangial cells stably expressing MLK 3, the PMA-induced increase in [3H]-thymidine incorporation was significantly reduced (> 50%). However, the PMA-induced increase in osteopontin mRNA was not affected by MLK 3 expression. To determine the mechanisms of these effects, activation of ERK2, JNK1 and p38 in response to PMA was examined in both vector and MLK 3 transfected cells. ERK2 activation was increased several fold by PMA in control cells but was attenuated significantly in MLK 3 expressing cells, suggesting that MLK 3 expression in mesangial cells can negatively regulate the ERK pathway. PMA had no significant effect on JNK and P38 activation, in either vector- or MLK 3-expressing cells. PD98059, a MEK inhibitor blocked PMA-induced DNA synthesis without affecting osteopontin expression. These results suggest that while protein kinase C activation increases cellular proliferation and osteopontin mRNA expression, over-expression of MLK 3 affects only the PKC-induced DNA synthesis, probably through inhibition of ERK. These results also indicate a novel mechanism of growth regulation by a member of the mixed-lineage kinase family that might have significant therapeutic implications in proliferative glomerulonephritis.
authors.affiliation: Department of Physiology, Michigan State University, East Lansing 48824, USA. paramesw@msu.edu
authors.forename: Narayanan
authors.initials: N
authors.lastname: Parameswaran
authors.forename: Carolyn S
authors.initials: CS
authors.lastname: Hall
authors.forename: Barbara C
authors.initials: BC
authors.lastname: Bock
authors.forename: Harvey V
authors.initials: HV
authors.lastname: Sparks
authors.forename: Kathleen A
authors.initials: KA
authors.lastname: Gallo
authors.forename: William S
authors.initials: WS
authors.lastname: Spielman
mesh_terms: D000818:Animals; D002455:Cell Division; D004261:DNA Replication / Q000187:drug effects*; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005419:Flavonoids / Q000494:pharmacology; D005920:Glomerular Mesangium / Q000187:drug effects / Q000201:enzymology / Q000378:metabolism*; D020930:MAP Kinase Kinase Kinases / Q000378:metabolism*; D008297:Male; D020928:Mitogen-Activated Protein Kinases / Q000037:antagonists & inhibitors; D053495:Osteopontin; D012333:RNA, Messenger / Q000235:genetics; D051381:Rats; D017207:Rats, Sprague-Dawley; D012795:Sialoglycoproteins / Q000235:genetics*; D013755:Tetradecanoylphorbol Acetate / Q000037:antagonists & inhibitors* / Q000494:pharmacology; D000097767:Mitogen-Activated Protein Kinase Kinase Kinase 11
chemical_list: D004791:Enzyme Inhibitors; D005419:Flavonoids; D020930:MAP Kinase Kinase Kinases; D020928:Mitogen-Activated Protein Kinases; D053495:Osteopontin; D012333:RNA, Messenger; D012795:Sialoglycoproteins; D013755:Tetradecanoylphorbol Acetate; D000097767:Mitogen-Activated Protein Kinase Kinase Kinase 11; C506895:SPP1 protein, human; C506897:Spp1 protein, rat; C093973:2-(2-amino-3-methoxyphenyl)-4H-1-benzopyran-4-one