Mechanisms of p16INK4A inactivation in non small-cell lung cancers.
The cyclin-dependent kinase inhibitor p16 (p16INK4A/CDKN2/MTS1) is a potent inhibitor of the cyclin D-dependent phosphorylation of the retinoblastoma gene (Rb) product, the inactivation of which induces loss of Rb-dependent G1 arrest through inappropriate phosphorylation of the Rb protein. To analyse the role of p16INK4A as a tumor suppressor in the genesis of non small cell lung cancers (NSCLC) and correlate loss of p16INK4A protein expression to genetic or epigenetic mechanisms, we have performed a comprehensive study of p16 status in a series of 43 NSCLC. To this end, we have investigated p16INK4A protein expression with immunohistochemistry, deletions of the gene by FISH, and determined the methylation status of exon 1alpha using a PCR-based methylation assay. Finally, possible mutations were studied by SSCP and subsequent sequencing. Twenty one of the 43 (49%) NSCLC studied exhibited an absence of p16INK4A nuclear staining. Of these, three (14%) had frameshift or missense mutations, seven (33%) displayed methylation of exon 1alpha and 10 (48%) displayed homozygous deletions. In total, 95% of the tumors with p16INK4A negative staining carried one of these three alternative genetic or epigenetic alterations. Furthermore, a high degree of chromosome 9 polysomy was found (58%) in those tumors with p16INK4A inactivation. Taken together these results suggest that deregulation of the p16 gene locus is a frequently occurring event in NSCLC through distinct mechanisms including rare point mutations, promotor methylation and frequent homozygous deletions. Furthermore, our data show that immunohistochemistry is a rapid and an accurate technique for screening of p16INK4A gene inactivation events that result in loss of protein expression.
Gazzeri
S
S
Groupe de recherche sur le cancer du poumon, DYOGEN, Institut Albert Bonniot, La Tronche, France.
Gouyer
V
V
Vour'ch
C
C
Brambilla
C
C
Brambilla
E
E
D000230:Adenocarcinoma / Q000235:genetics / Q000378:metabolism / Q000473:pathology; D002289:Carcinoma, Non-Small-Cell Lung / Q000235:genetics* / Q000378:metabolism / Q000473:pathology; D002294:Carcinoma, Squamous Cell / Q000235:genetics / Q000378:metabolism / Q000473:pathology; D002295:Carcinoma, Transitional Cell / Q000235:genetics / Q000378:metabolism / Q000473:pathology; D002899:Chromosomes, Human, Pair 9 / Q000235:genetics; D019941:Cyclin-Dependent Kinase Inhibitor p16 / Q000235:genetics* / Q000378:metabolism; D019175:DNA Methylation; D005091:Exons / Q000235:genetics; D017353:Gene Deletion; D015972:Gene Expression Regulation, Neoplastic; D016147:Genes, Tumor Suppressor / Q000235:genetics*; D006801:Humans; D017404:In Situ Hybridization, Fluorescence; D008175:Lung Neoplasms / Q000235:genetics* / Q000378:metabolism / Q000473:pathology; D009363:Neoplasm Proteins / Q000235:genetics* / Q000378:metabolism
D019941:Cyclin-Dependent Kinase Inhibitor p16; D009363:Neoplasm Proteins