SSeCKS/Gravin/AKAP12 inhibits cancer cell invasiveness and chemotaxis by suppressing a protein kinase C- Raf/MEK/ERK pathway.
SSeCKS/Gravin/AKAP12 ("SSeCKS") encodes a cytoskeletal protein that regulates G(1) --> S progression by scaffolding cyclins, protein kinase C (PKC) and PKA. SSeCKS is down-regulated in many tumor types including prostate, and when re-expressed in MAT-LyLu (MLL) prostate cancer cells, SSeCKS selectively inhibits metastasis by suppressing neovascularization at distal sites, correlating with its ability to down-regulate proangiogenic genes including Vegfa. However, the forced re-expression of VEGF only rescues partial lung metastasis formation. Here, we show that SSeCKS potently inhibits chemotaxis and Matrigel invasion, motility parameters contributing to metastasis formation. SSeCKS suppressed serum-induced activation of the Raf/MEK/ERK pathway, resulting in down-regulation of matrix metalloproteinase-2 expression. In contrast, SSeCKS had no effect on serum-induced phosphorylation of the Src substrate, Shc, in agreement with our previous data that SSeCKS does not inhibit Src kinase activity in cells. Invasiveness and chemotaxis could be restored by the forced expression of constitutively active MEK1, MEK2, ERK1, or PKCalpha. SSeCKS suppressed phorbol ester-induced ERK1/2 activity only if it encoded its PKC binding domain (amino acids 553-900), suggesting that SSeCKS attenuates ERK activation through a direct scaffolding of conventional and/or novel PKC isozymes. Finally, control of MLL invasiveness by SSeCKS is influenced by the actin cytoskeleton: the ability of SSeCKS to inhibit podosome formation is unaffected by cytochalasin D or jasplakinolide, whereas its ability to inhibit MEK1/2 and ERK1/2 activation is nullified by jasplakinolide. Our findings suggest that SSeCKS suppresses metastatic motility by disengaging activated Src and then inhibiting the PKC-Raf/MEK/ERK pathways controlling matrix metalloproteinase-2 expression and podosome formation.
Su
Bing
B
Department of Cancer Genetics, Roswell Park Cancer Institute, Buffalo, New York 14263, USA.
Bu
Yahao
Y
Engelberg
David
D
Gelman
Irwin H
IH
D054758:A Kinase Anchor Proteins / Q000235:genetics / Q000378:metabolism*; D015153:Blotting, Western; D018797:Cell Cycle Proteins / Q000235:genetics / Q000378:metabolism*; D045744:Cell Line, Tumor; D002633:Chemotaxis / Q000235:genetics / Q000502:physiology*; D004789:Enzyme Activation / Q000187:drug effects; D005455:Fluorescent Antibody Technique; D006801:Humans; D047468:Immunoprecipitation; D048369:MAP Kinase Kinase 1 / Q000378:metabolism; D048370:MAP Kinase Kinase 2 / Q000378:metabolism; D020778:Matrix Metalloproteinase 2 / Q000378:metabolism; D020929:Mitogen-Activated Protein Kinase Kinases / Q000378:metabolism*; D009362:Neoplasm Metastasis / Q000235:genetics; D010703:Phorbol Esters / Q000494:pharmacology; D011493:Protein Kinase C / Q000378:metabolism*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D015398:Signal Transduction / Q000187:drug effects / Q000235:genetics; D048490:raf Kinases / Q000378:metabolism*
D054758:A Kinase Anchor Proteins; C491162:AKAP12 protein, human; D018797:Cell Cycle Proteins; D010703:Phorbol Esters; C482128:MAP2K2 protein, human; D048490:raf Kinases; D011493:Protein Kinase C; D048369:MAP Kinase Kinase 1; D048370:MAP Kinase Kinase 2; C482125:MAP2K1 protein, human; D020929:Mitogen-Activated Protein Kinase Kinases; D020778:Matrix Metalloproteinase 2