Curcumin is a dietary pigment responsible for the yellow color of curry. It is a potent inhibitor of tumor promotion induced by 12-O-tetradecanoyl-phorbol-13-acetate (TPA) in mouse skin. When mouse fibroblast cells (NIH 3T3) were treated with TPA alone, protein kinase C (PKC) translocated from the cytosolic fraction to the particulate fraction. Treatment with 15 or 20 microns curcumin for 15 min inhibited TPA-induced PKC activity in particulate fraction by 26 or 60% and did not affect the level of PKC protein. Curcumin also inhibited PKC activity in both cytosolic and particulate fractions in vitro by competing with phosphatidylserine. However, the inhibitory effect of curcumin was reduced after preincubation with the thiol compounds. These findings suggest that the suppression of PKC activity may contribute to the molecular mechanism of inhibition of TPA-induced tumor promotion by curcumin.

No abstract

Matrix metalloproteinases (MMPs). produced by both infiltrating and resident cells of the periodontium, play a role in physiologic and pathologic events. It is recognized that an imbalance between activated MMPs and their endogenous inhibitors leads to pathologic breakdown of the extracellular matrix during periodontitis. To date, little is known about the regulation of MMP synthesis and secretion in human periodontal ligament fibroblasts (PDLFs). The purpose of this study was to examine the effects of cytokines, pharmacological agents (protein synthesis inhibitor and protein kinase C inhibitors) and predominant periodontal pathogens (Actinobacillus actinomycetemcomitans and Porphyromonas gingivalis) on MMP production in human PDLFs using gelatin zymography. The gelatin zymograms revealed that the main gelatinase secreted by human PDLFs migrated at 72 kDa and represents MMP-2. Minor gelatinolytic bands were also observed at 92 kDa regions that correspond to MMP-9. We found that A. actinomycetemcomitans, P. gingivalis and IL-1alpha can elevate MMP-2 secretion in human PDLFs. These results indicate that periodontal pathogens and inflammatory cytokines play an important role in tissue destruction and disintegration of extracellular matrix in periodontal diseases. Thus, activation of MMPs may be one of the distinct host degradative pathways in the pathogenesis of periodontitis. In addition, H7, staurosporine, cycloheximide and TGF-beta could suppress MMP-2 production. Agents that target protein synthesis or the protein kinase C pathway in human PDLFs inhibit MMP-2 production, and such inhibition may contribute to the pathogenesis of periodontal inflammation. Taken together, these findings suggest a possible new therapeutic approach, involving the use of drugs that modify host-response mechanisms to suppress or inhibit MMP-mediated tissue destruction.

No abstract

Protein kinase CA (PKCA) has been suggested to play an important role in tumorigenesis, invasion, and metastasis. In this study, we investigated the signal pathways selectively activated by PKCA in human hepatocellular carcinoma (HCC) cells to determine the role of mitogen-activated protein kinases (MAPK) in PKCA-mediated HCC migration and invasion. A stable SK-Hep-1 cell clone (siPKCA-SK) expressing DNA-based small interfering RNA (siRNA) PKCA was established and was then characterized by cell growth, migration, and invasion. The expression of PKCA was decreased in siPKCA-SK, and cell growth, migration, and invasion were reduced. These changes were associated with the decrease in p38 MAPK phosphorylation level, but not in c-jun-NH 2 -kinase-1/2 (JNK-1/2) and extracellular signal-regulated kinase-1/2 (ERK-1/2). This phenomenon was confirmed in the SK-Hep-1 cells treated with antisense PKCA olignucleotide. The p38 MAPK inhibitor SB203580 or dominant negative p38 mutant plasmid (DN-p38) was used to evaluate the dependency of p38 MAPK in PKCA-regulated migration and invasion. Attenuation of cell migration and invasion was revealed in the SKHep-1 cells treated with the SB203580 or DN-p38, but not with ERK-1/2 inhibitor PD98059 or JNK-1/2 inhibitor SP600125. Overexpression of constitutively active MKK6 or PKCA may restore the inactivation of p38 and the attenuation of cell migration and invasion in siPKCA-SK. Similar findings were observed in the stable HA22T/VGH cell clone expressing siRNA PKCA. This study provides new insight into the role of p38 MAPK in PKCA-mediated malignant phenotypes, especially in PKCA-mediated cancer cell invasion, which may have valuable implications for developing new therapies for some PKCAoverexpressing cancers. [Cancer Res 2007;67(9):4320-7]