Abstract
We have reported that TGF-beta-activated kinase-1 (TAK1) is constitutively over-expressed and phosphorylated in myeloma (MM) cells to mediate their growth and survival signaling. TAK1 expression and phosphorylation levels appear to be much higher in MM cells compared to their surrounding cells in bone marrow. In the present study, we therefore explored whether MM cells have a unique mechanism to augment the TAK1-mediated signaling. Okadaic acid, an inhibitor of protein phosphatase 2A (PP2A), a major serine and threonine protein phosphatase, further enhanced the phosphorylation levels of TAK1 in MM cells, whereas SMAP, an activator of PP2A, dose-dependently suppressed phosphorylation of TAK1 along with TAK1 protein levels to induce MM cell death, indicating the critical role of the suppression of PP2A activity in TAK1 phosphorylation and thereby MM cell growth and survival.
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