Silencing of the p18INK4c gene by promoter hypermethylation in Reed-Sternberg cells in Hodgkin lymphomas.
p18INK4c is a cyclin-dependent kinase (CDK) inhibitor that interferes with the Rb-kinase activity of CDK6/CDK4. Disruption of p18INK4c in mice impairs B-cell terminal differentiation and confers increased susceptibility to tumor development; however, alterations of p18INK4c in human tumors have rarely been described. We used a tissue-microarray approach to analyze p18INK4c expression in 316 Hodgkin lymphomas (HLs). Nearly half of the HL cases showed absence of p18INK4c protein expression by Reed-Sternberg (RS) cells, in contrast with the regular expression of p18INK4c in normal germinal center cells. To investigate the cause of p18INK4c repression in RS cells, the methylation status of the p18INK4c promoter was analyzed by methylation-specific polymerase chain reaction (PCR) and bisulfite sequencing. Hypermethylation of the p18INK4c promoter was detected in 2 of 4 HL-derived cell lines, but in none of 7 non-Hodgkin lymphoma (NHL)-derived cell lines. We also detected p18INK4c hypermethylation, associated with absence of protein expression, in 5 of 26 HL tumors. The correlation of p18INK4c immunostaining with the follow-up of the patients showed shorter overall survival in negative cases, independent of the International Prognostic Score. These findings suggest that p18INK4c may function as a tumor suppressor gene in HL, and its inactivation may contribute to the cell cycle deregulation and defective terminal differentiation characteristic of the RS cells.
Sánchez-Aguilera
Abel
A
Lymphoma Group, Molecular Pathology Program, and the Immunohistochemistry and Histology Unit, Centro Nacional de Investigaciones Oncológicas, E-28029 Madrid, Spain.
Delgado
Julio
J
Camacho
Francisca I
FI
Sánchez-Beato
Margarita
M
Sánchez
Lydia
L
Montalbán
Carlos
C
Fresno
Manuel F
MF
Martín
Carmen
C
Piris
Miguel A
MA
García
Juan F
JF
D018797:Cell Cycle Proteins / Q000235:genetics*; D045744:Cell Line, Tumor; D050763:Cyclin-Dependent Kinase Inhibitor p18; D019175:DNA Methylation; D015972:Gene Expression Regulation, Neoplastic; D020868:Gene Silencing; D006689:Hodgkin Disease / Q000235:genetics* / Q000401:mortality / Q000503:physiopathology; D006801:Humans; D008221:Lymphoid Tissue / Q000473:pathology / Q000503:physiopathology; D011401:Promoter Regions, Genetic / Q000502:physiology; D012326:RNA Splicing; D016539:Reed-Sternberg Cells / Q000502:physiology*; D012189:Retrospective Studies; D025521:Tumor Suppressor Proteins / Q000235:genetics*
C493971:CDKN2C protein, human; D018797:Cell Cycle Proteins; D050763:Cyclin-Dependent Kinase Inhibitor p18; D025521:Tumor Suppressor Proteins