Elevation of intracellular cyclic AMP inhibits NF-κB-mediated thymosin β4 expression in melanoma cells

Thymosin beta 4 (T beta 4) is a major actin-sequestering protein that has been implicated in the growth, survival, motility, and metastasis of certain tumors and is considered an indicator for malignant progression. Therefore, identifying compounds that can downregulate T beta 4 expression is very important for the development of anti-cancer chemotherapies. In this study, we investigated the effects of elevated cAMP on T beta 4 expression and the metastatic potential of murine B16 melanoma cells. In addition, we also dissected the mechanism underlying cAMP-mediated T beta 4 suppression. We found that treatment with the cAMP-inducing compounds alpha-MSH (alpha-melanocyte stimulating hormone) and IBMX (3-isobutyl-1-methylxanthine) significantly suppressed T beta 4 expression and regulated EMT-associated genes through the suppression of NF-kappa B activation in B16F10 cells. Along with decreased T beta 4 expression, the in vitro invasiveness and anchorage-independent growth in a semi-solid agar of these cells were also inhibited. In animal experiments, the metastatic potential of the alpha-MSH- or IBMX-treated B16F10 melanoma cells was decreased compared to untreated control cells. Collectively, our data demonstrate that elevated intracellular cAMP significantly Suppresses T beta 4 expression and reduces MMP-9 activity, which leads to decreased metastatic potential. Moreover, suppression of NF-kappa B activation by alpha-MSH or IBMX is critical for inhibiting T beta 4 expression. (C) 2009 Elsevier Inc. All rights reserved.