p38 MAPK activation, JNK inhibition, neoplastic growth inhibition, and increased gap junction communication in human lung carcinoma and Ras‐transformed cells by 4‐Phenyl‐3‐butenoic acid

Abstract

Human lung neoplasms frequently express mutations that down-regulate expression of various tumor suppressor molecules, including mitogen-activated protein kinases such as p38 MAPK. Conversely, activation of p38 MAPK in tumor cells results in cancer cell cycle inhibition or apoptosis initiated by chemotherapeutic agents such as retinoids or cisplatin, and is therefore an attractive approach for experimental anti-tumor therapies. We now report that 4-phenyl-3-butenoic acid (PBA), an experimental compound that reverses the transformed phenotype at non-cytotoxic concentrations, activates p38 MAPK in tumorigenic cells at concentrations and treatment times that correlate with decreased cell growth and increased cell-cell communication. H2009 human lung carcinoma cells and ras-transformed liver epithelial cells treated with PBA showed increased activation of p38 MAPK and its downstream effectors which occurred after 4 h and lasted beyond 48 h. Untransformed plasmid control cells showed low activation of p38 MAPK compared to ras-transformed and H2009 carcinoma cells, which correlates with the reduced effect of PBA on untransformed cell growth. The p38 MAPK inhibitor, SB203580, negated PBA’s activation of p38 MAPK downstream effectors. PBA also increased cell-cell communication and connexin 43 phosphorylation in ras-transformed cells, which were prevented by SB203580. In addition, PBA decreased activation of JNK, which is upregulated in many cancers. Taken together, these results suggest that PBA exerts its growth regulatory effect in tumorigenic cells by concomitant up-regulation of p38 MAPK activity, altered connexin 43 expression, and down-regulation of JNK activity. PBA may therefore be an effective therapeutic agent in human cancers that exhibit down-regulated p38 MAPK activity and/or activated JNK and altered cell-cell communication.

Mitogen-Activated Protein Kinase Signal Transduction in Solid Tumors

“…When referred to treatments, through control experiment, J Cell Biochem.et.al proved that PBA (an experimental compoun) had some therapeutic effectiveness, mainly by mechanisms such as increasing cell-cell communication, decreasing activation of JNK, up-regulation of p38 MAPK activity (Matesic et al, 2012). And Herbal medicines such as Radix Tetrastigma Hemsleyani Flavone (RTHF) can promote apoptosis via regulation of ERK and p38 phosphorylation (Zhong et al, 2013).…”

A Cell-Cell Communication Marker for Identifying Targeted Tumor Therapies

“…Combined treatment of the two compounds resulted in an approximately additive effect of the two compounds at the indicated concentrations (Figure 2). ChK and PBA administered alone also inhibited growth of H2009 human lung carcinoma cells [11,17]. …”

“…We have previously reported that ChK and PBA decrease phosphorylation of SAPK/JNK at the thr183/tyr185 activation sites [11, 17]. Figure 3A shows that WB-ras1 cells treated for 4 h with 2 or 5μM ChK showed decreased phosphorylation at this site site (lanes 5-8 compared to vehicle control lanes 2-4), and that the level of SAPK/JNK phosphorylation at 5μM ChK in these cells was similar to the level of SAPK/JNK phosphorylation in untreated non-transformed WB-neo3 cells (lane 9, and quantification in graph to the right).…”

“…PBA was obtained from Sigma-Aldrich (St. Louis, MO) and re-purified by re-crystallization before use in experiments. PBA-Me was synthesized as previously described [11]. p38 MAP kinase polyclonal antibody, Phospho-p38 MAP kinase (Thr180/Tyr182) polyclonal antibody, JNK polyclonal antibody, phospho-JNK (Thr183/Tyr185) polyclonal antibody, Akt polyclonal antibody, phospho-Akt (Ser473) polyclonal antibody, and anti-rabbit IgG alkaline phosphatase-conjugated antibody were from Cell Signaling Technology (Beverly, MA).…”

“…Chaetoglobosin K (ChK), a bioactive natural product [8], has been shown to suppress the tumorigenic phenotype in ras -transformed epithelial cells, to prevent tumor promoter-induced inhibition of intercellular communication, and to modulate the PI-3/Akt kinase pathway [9]. 4-phenyl-3-butenoic acid (PBA) is an experimental compound that has been shown to up-regulate cell-cell communication, reverse the transformed phenotype [10], and preferentially modulate the p38 MAPK pathway [11]. In this study, we compare the effects of ChK and PBA on upregulation of gap junction cell-cell communication, growth inhibition, and intracellular signaling pathways that regulate growth, providing insights into their biochemical mechanisms.…”