Impairment of MLH1 and CDKN2A in oncogenesis of laryngeal cancer

Abstract

Our study aimed at elucidating which genetic alterations tend to form a network and could be applied as molecular markers of larynx squamous cell carcinoma (LSCC). A panel of genes involved in tumorigenesis was investigated. To search for the possible mechanisms of gene silencing, loss of heterozygosity (LOH) was analysed followed by testing DNA methylation and protein expression for those genes found with the highest frequency of LOH (CDKN2A (55.4%), MLH1 (46.0%), RB1 (35.7%)). A correlation of both LOH and hypermethylation with the loss of expression for CDKN2A and MLH1 was found. Disrupted Rb pathway (loss of expression of RB1 and/or of CDKN2A) in 55.9% of analysed cases confirmed the hypothesis that RB1 pathway is altered in head and neck squamous cell carcinomas, with CDKN2A (45%), rather than RB1 (11.8%) being more frequently inactivated. In LSCC, LOH tends to occur together in gene pairs or triplets. The pair MLH1/CDKN2A and triplets MLH1/TSG on 8p22/CDKN2A and MLH1/ CDKN2A/RB1 are related to staging and grading. LOH in MLH1 correlates with lower and LOH in CDKN2A with higher grades of LSCC. It can be concluded that MLH1 and CDKN2A play an important role in LSCC development and progression.

Loss of heterozygosity for Rb locus and pRb immunostaining in laryngeal cancer: a clinicopathologic, molecular and immunohistochemical study.

“…Consistent with previous observation in head and neck cancer, it was found that 7 (10.4%) of the 67 informative cases had LOH of the Rb gene [11][12][13]. In our study low frequency of loss for Rb confirms the results obtained by Lee in head and neck cancer (15%) and Kannan in oral cancer (17%) [11,13].…”

“…Loss of heterozygosity at the retinoblastoma gene in the mentioned study of laryngeal supraglottic cancer [1) occurred at a frequency (59%) close to that found in non small cell cancer (48%) [14] or oesophageal cancer (54%) [10]. Nevertheless, for head and neck cancer LOH for Rb is rather infrequent [11][12][13]. Although, the reason for this high percentage of LOH for Rb in those studies might be connected with the chosen investigated group related only to supraglottic laryngeal cancer cases.…”

The clinical relevance of microsatellite alterations in head and neck squamous cell carcinoma: a critical review

“…The modern automatic fragment analysis procedures offer high throughput analysis and a more precise and quantitative 60 -64 Although other points of discussion are the cutoff values to be used for LOH ratios (the ratio between the peak height ratios of both alleles of normal and paired tumor sample), 9,39,63,65 there is fairly general agreement that appropriate cutoffs are 42 or o0.5. A last issue is on the different types of MSI.…”

“…17,18,19,33 There are several reports that LOH is associated with more advanced stage and more aggressive HNSCC tumors, 13,34,36,37,56 and specifically with nodal involvement. 32,44 Other authors describe very specific correlations such as a link between LOH at 17p and mitotic index, 39 a connection of LOH at MLH1 with lower grade HNSCC, and LOH at CDKN2A with higher grade, 9 or a preference of LOH in tumors originating from the pharynx. 56 A correlation between LOH and other patient-related factors like age and race, was described in some studies.…”

“…TSG loss is normally confirmed by investigating gene deletion or mutation, silencing by DNA methylation or concurrent loss of protein expression. 9 Prevalence of MSI and LOH in HSNCC MSI In HNSCC, the reported frequencies of MSI vary widely but in general the incidence is low leaving any significance unclear. Table 1 that shows the published studies till now on MSI in HNSCC indicates that the incidence varies from 3 21 to 88% 24 of MSI-H, largely depending on the number of patients, the loci and markers used, the patient age and detection methods.…”