Inhibition of the ubiquitin-proteasome pathway activates stress kinases and induces apoptosis in renal cancer cells.
The ubiquitin-proteasome pathway plays a critical role in the degradation of cellular proteins related to signal transduction. Cytokine and growth factor-dependent aberrant proliferation has been implicated in renal cell carcinoma (RCC). We hypothesized that inhibiting the proteasome function might activate a proapoptotic signal transduction by modulating the cytokine and growth factor related signal transduction pathway. We therefore investigated the effectiveness of a proteasome inhibitor in the treatment of RCC regarding the involvement of Mitogen-activated protein kinases (MAP kinases), because MAP kinases are major signal transduction molecules that are known to play a pivotal role in cancer cell proliferation or apoptosis triggered by extra-cellular cytokines and growth factors. A proteasome inhibitor, MG132 inhibited the proliferation of RCC cell lines, 786-O and KU20-01 in a time and dose-dependent manner. 786-O cells have truncated von-Hippel Lindau (VHL) tumor suppressor gene protein due to a one base pair deletion at exon 1, whereas KU20-01 cells have a wild-type VHL protein. MG132 induced apoptosis in both cell lines. The inhibition of the ubiquitin-proteasome pathways was confirmed by the accumulation of ubiquitin-tagged proteins. MG132 induced the phosphorylation of ERK at 4 h and thereafter persisted for 8 to 16 h. In contrast, JNK and p38 activation persisted for longer periods and remained enhanced until 24 h. The concomitant activation of effector caspases, caspase-3 and caspase-7 was observed in 786-O cells. The inhibition of the proteasome function can induce apoptosis in RCC irrespective of the VHL protein status. The persistence of JNK and p38 activation may therefore be a unique mechanism underlying MG132 induced apoptosis.
Department of Urology, Keio University School of Medicine, 35 Shinanomachi, Shinjuku-ku, Tokyo 160-8582, Japan.
Jo
J
Ishizawa
Shuichi
S
Yoshida
Mototsugu
M
Oya
Ryuichi
R
Mizuno
Toshiaki
T
Shinojima
Ken
K
Marumo
Masaru
M
Murai
D017209:Apoptosis; D002292:Carcinoma, Renal Cell / Q000201:enzymology* / Q000378:metabolism; D053148:Caspase 3; D053179:Caspase 7; D020169:Caspases / Q000378:metabolism; D045744:Cell Line, Tumor; D006801:Humans; D007680:Kidney Neoplasms / Q000201:enzymology* / Q000378:metabolism; D007976:Leupeptins / Q000494:pharmacology; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism*; D061988:Proteasome Inhibitors; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000378:metabolism; D014452:Ubiquitins / Q000378:metabolism*; D051020:bcl-X Protein
C494811:BCL2L1 protein, human; D007976:Leupeptins; D061988:Proteasome Inhibitors; D019253:Proto-Oncogene Proteins c-bcl-2; D014452:Ubiquitins; D051020:bcl-X Protein; D020928:Mitogen-Activated Protein Kinases; C505407:CASP3 protein, human; C505520:CASP7 protein, human; D053148:Caspase 3; D053179:Caspase 7; D020169:Caspases; C072553:benzyloxycarbonylleucyl-leucyl-leucine aldehyde