I-kappaBalpha depletion by transglutaminase 2 and mu-calpain occurs in parallel with the ubiquitin-proteasome pathway.
Transglutaminase 2 (TGase2) is a calcium-dependent, cross-linking enzyme that catalyzes iso-peptide bond formation between peptide-bound lysine and glutamine residues. TGase 2 can activate NF-kappaB through the polymerization-mediated depletion of I-kappaBalpha without IKK activation. This NF-kappaB activation mechanism is associated with drug resistance in cancer cells. However, the polymers cannot be detected in cells, while TGase 2 over-expression depletes free I-kappaBalpha, which raises the question of how the polymerized I-kappaBalpha can be metabolized in cells. Among proteasome, lysosome and calpain systems, calpain inhibition was found to effectively increase the accumulation of I-kappaBalpha polymers in MCF7 cells transfected with TGase 2, and induced high levels of I-kappaBalpha polymers as well in MDA-MB-231 breast cancer cells that naturally express a high level of TGase 2. Inhibition of calpain also boosted the level of I-kappaBalpha polymers in HEK-293 cells in case of TGase 2 transfection either with I-kappaBalpha or I-kappaBalpha mutant (S32A, S36A). Interestingly, the combined inhibition of calpain and the proteasome resulted in an increased accumulation of both I-kappaBalpha polymers and I-kappaBalpha, concurrent with an inhibition of NF-kappaB activity in MDA-MB-231 cells. This suggests that mu-calpain proteasome-dependent I-kappaBalpha polymer degradation may contribute to cancer progression through constitutive NF-kappaB activation.
Kim
Dae-Seok
DS
Cancer Cell and Molecular Biology Branch, National Cancer Center, Goyang, Gyeonggi-do 410-769, Republic of Korea.
Han
Byeong-Gu
BG
Park
Kang-Seo
KS
Lee
Byung Il
BI
Kim
Soo-Youl
SY
Bae
Chang-Dae
CD
D002154:Calpain / Q000235:genetics / Q000378:metabolism*; D045744:Cell Line, Tumor; D003538:Cystamine / Q000494:pharmacology; D004151:Dipeptides / Q000494:pharmacology; D019204:GTP-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D020672:I-kappa B Proteins / Q000037:antagonists & inhibitors / Q000378:metabolism*; D000072000:NF-KappaB Inhibitor alpha; D009369:Neoplasms / Q000378:metabolism* / Q000473:pathology; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism*; D000091345:Protein Glutamine gamma Glutamyltransferase 2; D034741:RNA, Small Interfering / Q000235:genetics; D011503:Transglutaminases / Q000235:genetics / Q000378:metabolism*; D025801:Ubiquitin / Q000378:metabolism*
D004151:Dipeptides; D020672:I-kappa B Proteins; C000606204:NFKBIA protein, human; D034741:RNA, Small Interfering; D025801:Ubiquitin; D000072000:NF-KappaB Inhibitor alpha; C071482:calpeptin; D000091345:Protein Glutamine gamma Glutamyltransferase 2; D011503:Transglutaminases; D002154:Calpain; C449002:mu-calpain; D046988:Proteasome Endopeptidase Complex; D019204:GTP-Binding Proteins; D003538:Cystamine