Molecular changes associated with oral dysplasia progression and acquisition of immortality: potential for its reversal by 5-azacytidine.
This study has identified molecular changes characteristic of early oral cancer progression. We reported previously that acquisition of the immortal phenotype is an early event in oral cancer development (F. McGregor et al., Cancer Res., 57: 3886-3889, 1997); our current data indicate that about half of oral dysplasia cultures are immortal, and this is associated with loss of expression of retinoic acid receptor (RAR)-beta and the cell cycle inhibitor p16(ink4a) (p16), p53 mutations, and increased levels of telomerase/human telomerase reverse transcriptase mRNA. In contrast, increased expression of the epidermal growth factor receptor, known to be a characteristic of oral cancer, does not occur until after the dysplasia stage in squamous cell carcinomas. Acquisition of invasive properties as judged by an in vitro Matrigel invasion assay also does not occur until the carcinoma stage and is further increased in metastases. Interestingly, one atypical mortal dysplasia with a considerably extended life span has lost expression of RAR-beta and p16, but it still expresses only wild-type p53 (albeit at a higher level than normal) and has not activated telomerase. RAR-beta and/or p16 re-expression can be induced by treatment with 5-aza-2-deoxycytidine (Aza-C) in some immortal dysplasias, and this has been shown to be due to silencing of gene expression by promoter methylation. Aza-C treatment also down-regulated telomerase activity and human telomerase reverse transcriptase mRNA. Interestingly, with one dysplasia, Aza-C was able to reverse its immortal phenotype, as judged by morphological criteria and expression of the senescence-associated acid beta-galactosidase activity during terminal growth arrest; this immortal dysplasia was the only one in which Aza-C treatment not only down-regulated telomerase activity but also induced re-expression of both RAR-beta and p16. The possibility of reversing the immortal phenotype of some dysplasias by Aza-C may be of clinical usefulness.
The Beatson Institute for Cancer Research, CRC Beatson Laboratories, Glasgow G61 1BD, Scotland.
Fiona
F
McGregor
Alessandra
A
Muntoni
Janis
J
Fleming
Judith
J
Brown
David H
DH
Felix
D Gordon
DG
MacDonald
E Kenneth
EK
Parkinson
Paul R
PR
Harrison
D000964:Antimetabolites, Antineoplastic / Q000494:pharmacology*; D001374:Azacitidine / Q000494:pharmacology*; D018797:Cell Cycle Proteins / Q000096:biosynthesis / Q000235:genetics; D002471:Cell Transformation, Neoplastic / Q000187:drug effects* / Q000235:genetics / Q000378:metabolism*; D002478:Cells, Cultured; D019941:Cyclin-Dependent Kinase Inhibitor p16 / Q000096:biosynthesis / Q000235:genetics; D050759:Cyclin-Dependent Kinase Inhibitor p21; D050760:Cyclin-Dependent Kinase Inhibitor p27; D016213:Cyclins / Q000096:biosynthesis / Q000235:genetics; D004268:DNA-Binding Proteins; D018450:Disease Progression; D066246:ErbB Receptors / Q000096:biosynthesis / Q000235:genetics; D006801:Humans; D009061:Mouth Mucosa / Q000378:metabolism / Q000473:pathology*; D009062:Mouth Neoplasms / Q000235:genetics / Q000378:metabolism / Q000473:pathology / Q000517:prevention & control; D011230:Precancerous Conditions / Q000188:drug therapy* / Q000235:genetics / Q000378:metabolism* / Q000473:pathology; D011494:Protein Kinases / Q000096:biosynthesis / Q000235:genetics; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins; D012333:RNA, Messenger / Q000096:biosynthesis / Q000235:genetics; D018168:Receptors, Retinoic Acid / Q000096:biosynthesis / Q000235:genetics; D019098:Telomerase / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism; D016159:Tumor Suppressor Protein p53 / Q000096:biosynthesis / Q000235:genetics; D025521:Tumor Suppressor Proteins / Q000096:biosynthesis / Q000235:genetics; D000097869:Polo-Like Kinase 1
D000964:Antimetabolites, Antineoplastic; D001374:Azacitidine; D018797:Cell Cycle Proteins; D019941:Cyclin-Dependent Kinase Inhibitor p16; D050759:Cyclin-Dependent Kinase Inhibitor p21; D050760:Cyclin-Dependent Kinase Inhibitor p27; D016213:Cyclins; D004268:DNA-Binding Proteins; D066246:ErbB Receptors; D011494:Protein Kinases; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins; D012333:RNA, Messenger; D018168:Receptors, Retinoic Acid; D019098:Telomerase; D016159:Tumor Suppressor Protein p53; D025521:Tumor Suppressor Proteins; D000097869:Polo-Like Kinase 1; C493956:CDKN1A protein, human; C082925:retinoic acid receptor beta