Induction of p16INK4A mediated by beta-catenin in a TCF4-independent manner: implications for alterations in p16INK4A and pRb expression during trans-differentiation of endometrial carcinoma cells.
Excessive beta-catenin is considered to contribute to tumor progression by inducing transcription of cell cycle-related genes such as cyclin D1 and c-myc. In contrast, our recent studies demonstrated that beta-catenin could inhibit cell proliferation through activation of p14(ARF)/p53/p21(WAF1) pathway during trans-differentiation toward morular phenotype of endometrial carcinoma (Em Ca) cells. Here, we focused on associations with alterations in p16(INK4A) and pRb expression during this process. In clinical cases, p16(INK4A) immunoreactivity was found to frequently overlap with nuclear beta-catenin accumulation in small-sized morules and surrounding glandular carcinomas (Sur-Ca), demonstrating a significant positive correlation (r = 0.447, p < 0.0001) overall, while the immunoreactions showed stepwise decrease in enlarged morules, despite persistent accumulation of beta-catenin and p21(WAF1) in nuclei. Immunoreactivity for both total pRb and its phosphorylated form was apparently decreased in all morules as compared to Sur-Ca lesions, with a significantly positive correlation. In cell lines, transcriptional activation of p16(INK) (4A) promoter by active form beta-catenin, as well as p21(WAF1), occurred through the region from -385 to -280 bp relative to the translation start site, in a TCF4-independent manner. Moreover, cell proliferation was accompanied with phosphorylation of pRb and increased p16(INK4A) expression, while its inhibition by serum starvation caused decreased expression of total pRb but not p16(INK4A), resulting in high relative amounts of the latter. These findings indicate that induction of p16(INK4A) mediated by nuclear beta-catenin and p21(WAF1), along with loss of pRb expression, may be important for initial steps during trans-differentiation of Em Ca cells. In addition, its down-regulation is associated with progression of lesions.
Saegusa
Makoto
M
Department of Pathology, Kitasato University School of Medicine, Sagamihara, Kanagawa 228-8555, Japan. msaegusa@med.kitasato-u.ac.jp
Hashimura
Miki
M
Kuwata
Takeshi
T
Hamano
Mieko
M
Okayasu
Isao
I
D015153:Blotting, Western; D002454:Cell Differentiation; D019941:Cyclin-Dependent Kinase Inhibitor p16 / Q000378:metabolism*; D050759:Cyclin-Dependent Kinase Inhibitor p21 / Q000378:metabolism*; D018450:Disease Progression; D015536:Down-Regulation; D016889:Endometrial Neoplasms / Q000378:metabolism*; D005260:Female; D005455:Fluorescent Antibody Technique; D015972:Gene Expression Regulation, Neoplastic; D006801:Humans; D009028:Morula; D010957:Plasmids; D016160:Retinoblastoma Protein / Q000378:metabolism*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D051820:TCF Transcription Factors / Q000378:metabolism; D058118:Transcription Factor 7-Like 2 Protein; D015533:Transcriptional Activation; D014407:Tumor Cells, Cultured; D025803:Tumor Suppressor Protein p14ARF / Q000378:metabolism; D016159:Tumor Suppressor Protein p53 / Q000378:metabolism; D051176:beta Catenin / Q000378:metabolism*
C493956:CDKN1A protein, human; D019941:Cyclin-Dependent Kinase Inhibitor p16; D050759:Cyclin-Dependent Kinase Inhibitor p21; D016160:Retinoblastoma Protein; D051820:TCF Transcription Factors; C544894:TCF7L2 protein, human; D058118:Transcription Factor 7-Like 2 Protein; D025803:Tumor Suppressor Protein p14ARF; D016159:Tumor Suppressor Protein p53; D051176:beta Catenin