Abstract
Protein kinase C (PKC) has been implicated in carcinogenesis and displays variable expression profiles during cancer progression. Studies of dietary phytochemicals on cancer signalling pathway regulation have been conducted to search for potent signalling regulatory agents. The present study was designed to evaluate any suppressive effect of maslinic acid on PKC expression in human B-lymphoblastoid cells (Raji cells), and to identify the PKC isoforms expressed. Effects of maslinic acid on PKC activity were determined using a PepTag assay for non-radioactive detection of PKC. The highest expression in Raji cells was obtained at 20 nM PMA induced for 6 hours. Suppressive effects of maslinic acid were compared with those of four PKC inhibitors (H- 7, rottlerin, sphingosine, staurosporine) and two triterpenes (oleanolic acid and ursolic acid). The IC₅₀ values achieved for maslinic acid, staurosporine, H-7, sphingosine, rottlerin, ursolic acid and oleanolic acid were 11.52, 0.011, 0.767, 2.45, 5.46, 27.93 and 39.29 μM, respectively. Four PKC isoforms, PKC βI, βII, δ, and ζ, were identified in Raji cells via western blotting. Maslinic acid suppressed the expression of PKC βI, δ, and ζ in a concentration-dependent manner. These preliminary results suggest promising suppressive effects of maslinic acid on PKC activity in Raji cells. Maslinic acid could be a potent cancer chemopreventive agent that may be involved in regulating many downstream signalling pathways that are activated through PKC receptors.
Highlights
The incidence and mortality rates of cancer have increased yearly and the four most frequent cancers are lung, breast, colorectal and stomach cancers (Ferlay et al, 2004)
The IC50 values achieved for maslinic acid, staurosporine, H-7, sphingosine, rottlerin, ursolic acid and oleanolic acid were 11.52, 0.011, 0.767, 2.45, 5.46, 27.93 and 39.29 μM, respectively
Four Protein kinase C (PKC) inhibitors, H-7, rottlerin, sphingosine monoclonal or polyclonal antibodies against various and staurosporine and two other triterpenes, oleanolic isoforms of PKC (Santa Cruz Biotechnology, USA) at a acid and ursolic acid were employed to benchmark the dilution of 1:500, 1:1000
Summary
The incidence and mortality rates of cancer have increased yearly and the four most frequent cancers are lung, breast, colorectal and stomach cancers (Ferlay et al, 2004). This study and the separated proteins were transferred onto was designed to evaluate the inhibitory effect of an Immobilon PVDF (poly-vinylidene-difluoride) maslinic acid, a novel natural triterpene on protein kinase membrane. Four PKC inhibitors, H-7, rottlerin, sphingosine monoclonal or polyclonal antibodies against various and staurosporine and two other triterpenes, oleanolic isoforms of PKC (Santa Cruz Biotechnology, USA) at a acid and ursolic acid were employed to benchmark the dilution of 1:500 (for PKCδ), 1:1000 The enzyme-coupled was performed to identify the PKC isoforms suppressed secondary antibody Raji cells obtained from Riken Cell Bank, Japan PKC was determined by treating cells with different were maintained in commercial Roswell Park Memorial concentrations of PMA and incubation times. This transient PKC activation pattern is consistent with other studies reporting that higher
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