The proteosome inhibitor MG132 attenuates Retinoic Acid Receptor trans-activation and enhances trans-repression of Nuclear Factor κB. Potential relevance to chemo-preventive interventions with retinoids

Valentine B Andela¹ and Randy N Rosier²

¹Department of Orthopaedics & The James P. Wilmot Cancer Center, University of Rochester Medical Center, 601 Elmwood Avenue Box 665, Rochester, New York, 14642, USA

²Department of Orthopaedics, University of Rochester Medical Center, 601 Elmwood Avenue Box 665, Rochester, New York, 14642, USA

author email corresponding author email

Molecular Cancer 2004, 3:8doi:10.1186/1476-4598-3-8


Published:	22 March 2004

Abstract

Background

Nuclear factor kappa B (NFκB) is a pro-malignant transcription factor with reciprocal effects on pro-metastatic and anti-metastatic gene expression. Interestingly, NFκB blockade results in the reciprocal induction of retinoic acid receptors (RARs). Given the established property of RARs as negative regulators of malignant progression, we postulated that reciprocal interactions between NFκB and RARs constitute a signaling module in metastatic gene expression and malignant progression. Using Line 1 tumor cells as a model for signal regulation of metastatic gene expression, we investigated the reciprocal interactions between NFκB and RARs in response to the pan-RAR agonist, all-trans retinoic acid (at-RA) and the pan-RAR antagonist, AGN193109.

Results

At-RA [0.1–1 μM] dose-dependently activated RAR and coordinately trans-repressed NFκB, while AGN193109 [1–10 μM] dose-dependently antagonized the effects of at-RA. At-RA and AGN193109 reciprocally regulate pro-metastatic matrix metalloprotease 9 (MMP 9) and its endogenous inhibitor, the tissue inhibitor of metalloprotease 1 (TIMP 1), in a manner consistent with the putative roles of NFκB and RAR in malignant progression. Activation of RAR concurs with its ubiquitination and proteosomal degradation. Accordingly, the proteosome inhibitor, MG132 [5 μM], blocked RAR degradation, quelled RAR trans-activation and enhanced RAR trans-repression of NFκB.

Conclusion

We conclude that reciprocal interactions between NFκB and RARs constitute a signaling module in metastatic gene expression and malignant progression and propose that the dissociative effect of proteosome inhibitors could be harnessed towards enhancing the anticancer activity of retinoids.