title: Loss of p16/INK4A protein expression in non-Hodgkin's lymphomas is a frequent finding associated with tumor progression.
abstract: 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.
authors.affiliation: Department of Genetics, Virgen de la Salud Hospital, Toledo, Spain.
authors.forename: R
authors.initials: R
authors.lastname: Villuendas
authors.forename: M
authors.initials: M
authors.lastname: Sánchez-Beato
authors.forename: J C
authors.initials: JC
authors.lastname: Martínez
authors.forename: A I
authors.initials: AI
authors.lastname: Saez
authors.forename: B
authors.initials: B
authors.lastname: Martinez-Delgado
authors.forename: J F
authors.initials: JF
authors.lastname: García
authors.forename: M S
authors.initials: MS
authors.lastname: Mateo
authors.forename: L
authors.initials: L
authors.lastname: Sanchez-Verde
authors.forename: J
authors.initials: J
authors.lastname: Benítez
authors.forename: P
authors.initials: P
authors.lastname: Martínez
authors.forename: M A
authors.initials: MA
authors.lastname: Piris
mesh_terms: 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
chemical_list: D019941:Cyclin-Dependent Kinase Inhibitor p16; D017931:DNA Primers; D011506:Proteins; D025803:Tumor Suppressor Protein p14ARF