Loss of p16/INK4A protein expression in non-Hodgkin's lymphomas is a frequent finding associated with tumor progression.
The CDKN2A gene located on chromosome region 9p21 encodes the cyclin-dependent kinase-4 inhibitor p16/INK4A, a negative cell cycle regulator. We analyzed p16/INK4A expression in different types of non-Hodgkin's lymphoma to determine whether the absence of this protein is involved in lymphomagenesis, while also trying to characterize the genetic events underlying this p16/INK4A loss. To this end, we investigated the levels of p16/INK4A protein using immunohistochemical techniques in 153 cases of non-Hodgkin's lymphoma, using as reference the levels found in reactive lymphoid tissue. The existence of gene mutation, CpG island methylation, and allelic loss were investigated in a subset of 26 cases, using single-strand conformational polymorphism and direct sequencing, Southern Blot, polymerase chain reaction, and microsatellite analysis, respectively. Loss of p16/INK4A expression was detected in 41 of the 112 non-Hodgkin's lymphomas studied (37%), all of which corresponded to high-grade tumors. This loss of p16/INK4A was found more frequently in cases showing tumor progression from mucosa-associated lymphoid tissue low-grade lymphomas (31 of 37) or follicular lymphomas (4 of 4) into diffuse large B-cell lymphomas. Analysis of the status of the p16/INK4A gene showed different genetic alterations (methylation of the 5'-CpG island of the p16/INK4A gene, 6 of 23 cases; allelic loss at 9p21, 3 of 16 cases; and nonsense mutation, 1 of 26 cases). In all cases, these events were associated with loss of the p16/INK4A protein. No case that preserved protein expression contained any genetic change. Our results demonstrate that p16/INK4A loss of expression contributes to tumor progression in lymphomas. The most frequent genetic alterations found were 5'-CpG island methylation and allelic loss.
Villuendas
R
R
Department of Genetics, Virgen de la Salud Hospital, Toledo, Spain.
Sánchez-Beato
M
M
Martínez
J C
JC
Saez
A I
AI
Martinez-Delgado
B
B
García
J F
JF
Mateo
M S
MS
Sanchez-Verde
L
L
Benítez
J
J
Martínez
P
P
Piris
M A
MA
D002478:Cells, Cultured; D002899:Chromosomes, Human, Pair 9 / Q000235:genetics; D019941:Cyclin-Dependent Kinase Inhibitor p16 / Q000235:genetics / Q000378:metabolism*; D017931:DNA Primers / Q000737:chemistry; D018450:Disease Progression; D005434:Flow Cytometry; D006801:Humans; D007124:Immunoenzyme Techniques; D019656:Loss of Heterozygosity; D008228:Lymphoma, Non-Hodgkin / Q000235:genetics / Q000378:metabolism* / Q000473:pathology*; D008745:Methylation; D018613:Microscopy, Confocal; D016133:Polymerase Chain Reaction; D011506:Proteins / Q000235:genetics / Q000378:metabolism; D025803:Tumor Suppressor Protein p14ARF
D019941:Cyclin-Dependent Kinase Inhibitor p16; D017931:DNA Primers; D011506:Proteins; D025803:Tumor Suppressor Protein p14ARF