Characteristics of antitumor activity of mutant type p27^Kip1 gene in an oral cancer cell line

Abstract 

It is well known that loss of the cyclin-dependent kinase inhibitor p27^Kip1 protein correlates with the poor prognosis of various cancers including oral squamous cell carcinoma (SCC). Posttranslational degradation of p27^Kip1 protein is mediated by phosphorylation of Thr-187 of p27^Kip1 protein, which follows ubiquitination. In this study, we constructed an expression vector expressing mutant type p27^Kip1 gene (pcDNA3.1–p27^Kip1 mt), with mutation of Thr-187/Pro-188 (ACGCCC) to Met-187/Ile-188 (ATGATC), which is not influenced by ubiquitin-mediated degradation. We transfected mutant and wild type p27^Kip1 genes into an oral SCC cell line, B88 to up-regulate the expression of mutant or wild p27^Kip1 gene in each transfectant. B88-p27^Kip1 mt showed significant growth inhibition than B88-p27^Kip1 wt or B88-neo in vitro (p<0.01). Also, both types of B88-p27^Kip1 showed G1 arrest and apoptosis, however, B88-p27^Kip1 mt showed remarkable G1 arrest. In addition, B88-p27^Kip1 mt and B88-p27^Kip1 wt showed markedly inhibition of the migration and out-growth of cancer cells than B88-p27^Kip1 wt or B88-neo. Moreover, B88-p27^Kip1 mt also showed remarkable suppression of tumor growth and cervical lymph metasasis than B88-p27^Kip1 wt or B88-neo in vivo (p<0.01). In short, the mutant type p27^Kip1 gene could show more potent antitumor effects than wild type p27^Kip1 gene in B88 cells. These findings suggest that mutant type p27^Kip1 gene has the potential to become a novel and powerful gene therapy tool for patients with oral cancers.

Keywords:  Gene therapy, Mutant type p27^Kip1 gene, Oral cancer, Antitumor activity