Proteasome 26S is a major enzyme system catalysing the degradation of intracellular proteins involved in the regulation of many processes such as cell apoptosis, survival, and inflammatory response including IκBα, transcription factor’s NFκB protein subunit, and AP-1 controlling enzyme – c-Jun N-terminal kinase (JNK). Our previous studies have shown that plant stilbene derivatives: resveratrol (RES) and pterostilbene (PTE) affected the activation of NFκB and AP-1 stimulated by tumor promoter, 12-O-tertadecanoylphorbol 13-acetate (TPA) in mouse skin.

The aim of the present study was to evaluate weather the inhibition of these transcription factors activation, may result from proteasome 26S inhibition.

The proteasome 26S peptidase activity was assayed with the use of synthetic fluorigenic peptide substrate (Suc-Leu-Leu-Val-Tyr-AMC). The effect of RES and PTE was determined in vitro and in vivo in epidermal extracts from mice treated with TPA. TPA was applied in three consecutive days, and 4 hours after the last treatment mice were sacrificed and epidermis was isolated. In in vitro study the effect of RES and PTE on proteasome 26S peptidase activity in the concentration range of 10-150 μM was evaluated. To study the effect of both stilbenes in vivo mice were pretreated with 16 μmoles of RES or PTE per mice 15 minutes before the TPA treatment.

The results of our study show that the tested compounds are capable to modulate TPA-stimulated proteasome 26S activity which may affect the NFκB or AP-1 activation. Collectively the results of our present and earlier studies suggest that these compounds are capable of affecting more than one critical pathway of carcinogenesis and thus will have greater advantage over other single-target potential chemopreventive agents.

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