Molecular predictive factors for progression of high-grade preinvasive bronchial lesions.

RATIONALE: The outcome of precancerous bronchial lesions is not well known, and their management is subject to controversy. Many molecular alterations are present in preinvasive lesions, but none has been assessed to predict the evolution of the lesions. OBJECTIVES: To analyze the outcome of high-grade precancerous lesions according to their molecular profile. METHODS: Twenty-three severe dysplasia and 31 carcinoma in situ (CIS) lesions in 37 patients were monitored using repeated autofluorescence bronchoscopy over a 12-year period. Microdissection and polymerase chain reaction analysis were performed on paraffin tissue sections to assess loss of heterozygosity (LOH) and microsatellite instability on chromosome 3p, 5q, and 9p. Histology and molecular status at baseline were compared between 7 lesions that became invasive, 11 that relapsed after treatment, 17 that were eradicated with local treatment, and 19 that spontaneously regressed. MEASUREMENTS AND MAIN RESULTS: Ninety-four percent of lesions that progressed or relapsed were CIS at baseline, whereas 79% of spontaneously regressing lesions were severe dysplasia (P < 0.0001). 3p and 9p LOH was more frequent in CIS than in severe dysplasia (P = 0.03). In the whole group of lesions as well as in the CIS group, 3p LOH was strongly associated with progression (P < 0.0001 and P = 0.02, respectively). Microsatellite instability was not associated with the outcome of the lesions. A therapeutic strategy based on the presence of 3p or 9p LOH would have led to overtreatment of six lesions but would have missed only 1 among the 18 progressing lesions. CONCLUSIONS: Baseline histology and 3p LOH analysis appear to be useful in predicting the outcome of high-grade precancerous lesions.

Inactivation of the RRB1-Pescadillo pathway involved in ribosome biogenesis induces chromosomal instability.

Since chromosomal instability (CIN) is a hallmark of most cancer cells, it is essential to identify genes whose alteration results into this genetic instability. Using a yeast CIN indicator strain, we show that inactivation of the YMR131c/RRB1 gene, which is involved in early ribosome assembly and whose expression is induced when the spindle checkpoint is activated, alters chromosome segregation and blocks mitosis at the metaphase/anaphase transition. We demonstrate that RRB1 interacts with YPH1 (yeast pescadillo homologue 1) and other members of the Yph1 complex, RPL3, ERB1 and ORC6, involved in ribosome biogenesis and DNA replication. Transient depletion of the human homologues GRWD, Pescadillo, Rpl3, Bop1 and Orc6L resulted in an increase of abnormal mitoses with appearance of binucleate or hyperploid cells, of cells with multipolar spindles and of aberrant metaphase plates. If deregulation of proteins involved in ribosome biogenesis, commonly observed in malignant tumors, could contribute to cancer through an aberrant protein synthesis, our study demonstrates that alteration of proteins linking ribosome biogenesis and DNA replication may directly cause CIN.

Aberrant methylation of the CDKN2a/p16INK4a gene promoter region in preinvasive bronchial lesions: a prospective study in high-risk patients without invasive cancer.

Among the identified factors involved in malignant transformation, abnormal methylation of the CDKN2A/p16(INK4a) gene promoter has been described as an early event, particularly in bronchial cell cancerization. Precancerous bronchial lesions (n = 70) prospectively sampled during fluorescence endoscopy in a series of 37 patients at high risk for lung cancer were studied with respect to the methylation status of the CDKN2A gene. Methylation-specific polymerase chain reaction was performed on DNA extracted from pure bronchial cell populations derived from biopsies and detection of p16 protein was studied by immunohistochemistry on contiguous parallel biopsies. Aberrant methylation of the CDKN2A gene promoter was found in 19% of preinvasive lesions and its frequency increased with the histologic grade of the lesions. Methylation in at least 1 bronchial site was significantly more frequent in patients with cancer history, although there was no difference in the outcome of patients with or without methylation in bronchial epithelium. The other risk factors studied (tobacco and asbestos exposure) did not influence the methylation status. There was no relationship between CDKN2A methylation and the evolutionary character of the lesions. Our results confirm that abnormal methylation of the CDKN2A gene promoter is an early event in bronchial cell cancerization, which can persist for several years after carcinogen exposure cessation, and show that this epigenetic alteration cannot predict the evolution of precancerous lesions within a 2-year follow-up.

Overexpression of B-type cyclins alters chromosomal segregation.

To identify genes which overexpression results into chromosomal instability (CIN), we developed a biological approach based on a yeast indicator strain in which CIN can be detected by a sectoring phenotype. Screening in this strain of a yeast genomic library cloned into a high copy vector led us to identify, among the clones generating 100% of sectoring colonies, Clb5, one of the six B-type cyclins present in yeast. Overexpression of cyclin B2 and cyclin B1, the two human homologs of Clb5, in the CIN indicator strain resulted also into a sectoring phenotype and induced, like overexpression of Clb5, an abnormal sensitivity to benomyl, indicating that overexpression of B-type cyclins alters the spindle checkpoint. In a series of 38 primary colorectal cancers, we detected in five tumors (13%) an accumulation of cyclin B1, which was neither related to mRNA overexpression nor to mutation within the coding region, and in five other tumors (13%) a 2-10-fold increase of cyclin B2 mRNA which was not related to gene amplification. These results suggest that overexpression of cyclins B, resulting from different mechanisms, could contribute, through an alteration of the spindle checkpoint, to the chromosomal instability observed in cancer.