The p21-activated kinases (PAKs) are a family of serine/threonine protein kinases and activated by binding with activated Rho GTPases such as Rac or Cdc42. PAKs regulate actin cytoskeletal remodeling, cell motility, cell survival, and apoptosis. Also, PAKs are involved in several diseases such as cancer, virus infectious diseases, mental retardation, Alzheimer and Parkinson's diseases. Therefore, the substances that are able to inhibit PAK activation can be used as powerful tools and medicines for PAK relative diseases or specific inhibitors for study of PAK signaling pathway. In this study, we investigated and characterized the 5 compounds of 4-benzene-1, 2-naphthoquinone (NQ) family as candidate substances to inhibit the PAK1 activation in vitro and in cells. Binding between p21-binding domain (PBD) of PAK1 and Cdc42 was blocked by 5 NQ-compounds in ELISA assay. Myelin basic protein (MBP) phosphorylation was dramatically reduced by treatment of these compounds in vitro kinase assay for Cdc42-induced or constitutive active PAK1 mutant. Also, phosphorylation at Thr 423 of transfected PAK1 was inhibited by treatment of 5 NQ-compounds in 293T cells, respectively. Finally, NQ-5 inhibited strongly the PAK1 activation by PDGF stimulation and cell motility in PDGF-induced wound migration assay in NIH 3T3 cells. Therefore, these NQ compounds will be good candidates as target molecules to regulate PAK1-related diseases or inhibitors to study PAK1 signaling pathway.

Retinoic acid plays an important role in the regulation of cell growth and differentiation. In our present study, we evaluated the effects of all-trans retinoic acid (RA) on cell proliferation and on the cell cycle regulation of human gingival fibroblasts (HGFs). Cell proliferation was assessed using the MTT assay. Cell cycle analysis was performed by flow cytometry, and cell cycle regulatory proteins were determined by western blot. Cell proliferation was increased in the presence of a 0.1 nM to 1μM RA dose range, and maximal growth stimulation was observed in cells exposed to 1 nM of RA. Exposure of HGFs to 1 nM of RA resulted in an augmented cell cycle progression. To elucidate the molecular mechanisms underlying cell cycle regulation by RA, we measured the intracellular levels of major cell cycle regulatory proteins. The levels of cyclin E and cyclin-dependent kinase (CDK) 2 were found to be increased in HGFs following 1 nM of RA treatment. However, the levels of cyclin D, CDK 4, and CDK 6 were unchanged under these conditions. Also after exposure to 1 nM of RA, the protein levels of p21 WAF1/CIP1 and p16 INK4A were decreased in HGFs compared with the control group, but the levels of p53 and pRb were similar between treated and untreated cells. These results suggest that RA increases cell proliferation and cell cycle progression in HGFs via increased cellular levels of cyclin E and CDK 2, and decreased cellular levels of p21 WAF1/CIP1 and p16 INK4A.

It is well known that the imbalance between epithelial cell growth and inhibitor factors may cause human epithelial cancer. Over-expression of the epidermal growth factor receptor(EGFR) has been implicated in the development of oral squamous cell carcinoma. ZD1839 inhibits selectively the EGFR tyrosine kinase activity and is clinically used for cancer patients. However the mechanisms by which it exerts its anti-tumor activity remains unclear. This study attempted to determine the mechanisms underlying the effects of ZD1839 on the cellular level and to characterize the effects of ZD1839 with regard to human oral squamous cell carcinoma(OSCC) cell growth. The YD-10B and YD-38 cell lines established from OSCC in the department of Oral Pathology, Yonsei University College of Dentistry and ZD1839(Iressa) were used for this study. The inhibition of cell proliferation induced by ZD1839 was reversible and the lowest dose of ZD1839 that produced statistically significant growth inhibition in YD cell lines were 0.1 μM. The delay in cell cycle progression was induced by 0.1 μM of ZD1839 treatment after 24 hr. This reduction in cell proliferation and cell cycle delay were associated with up-regulation of the cyclin dependent kinase inhibitor(CDKI), P21CIP1/WAF1 and P27KIP1. Reduced expression of cyclin D1 was also observed after treatment with ZD 1839 to YD-38 cells but not to YD-38. The present results suggest that the antiproliferative effects of ZD1839, in vitro was associated with degradation of cyclin D1, which may be used as a possible indicator of a high cell sensitivity to ZD1839.