Detection and cloning of potent transforming gene(s) from chewing tobacco-related human oral carcinomas

Prevalence of K-RAS Codons 12 and 13 Mutations in Locally Advanced Head and Neck Squamous Cell Carcinoma and Impact on Clinical Outcomes

Background. RAS gene mutations have an impact on treatment response and overall prognosis for certain types of cancer. Objectives. To determine the prevalence and impact of K-RAS codons 12 and 13 mutations in patients with locally advanced HNSCC treated with primary or adjuvant chemo-radiation. Methods. 428 consecutive patients were treated with chemo-radiation therapy and followed for a median of 37 months. From these, 199 paraffin embedded biopsy or surgical specimens were retrieved. DNA was isolated and analyzed for K-RAS mutational status. Results. DNA extraction was successful in 197 samples. Of the 197 specimens, 3.5% presented K-RAS codon 12 mutations. For mutated cases and non-mutated cases, complete initial response to chemoradiation therapy was 71 and 73% (P = 0.32). LRC was respectively 32 and 83% (P = 0.03), DFS was 27 and 68% (P = 0.12), distant metastasis-free survival was 100 and 81% (P = 0.30) and OS was 57 and 65% (P = 0.14) at three years. K-Ras codon 13 analysis revealed no mutation. Conclusion. K-RAS codon 12 mutational status, although not associated with a difference in response rate, may influence the failure pattern and the type of therapy offered to patients with HNSCC. Our study did not reveal any mutation of K-RAS codon 13.

Molecular cloning, isolation and characterisation of ERK3 gene from chewing-tobacco induced oral squamous cell carcinoma

The mitogen activated serine/threonine kinases (MAPKs) constitute extracellular signal-regulated protein kinases (ERKs), c-Jun N-terminal kinases (JNKs) and p38 MAPK, with an important role in cell proliferation and transformation. Earlier studies from our laboratory had indicated a role for MAPK pathway in oral cancer. Our current study was aimed at examining the role of a MAPK-ERK3, in chewing-tobacco associated oral squamous cell carcinoma. We constructed a cDNA library from primary oral cancer tissue, cloned and isolated the ERK3 gene. The gene was sequenced and the sequence submitted to GenBank (Accession number AF420474). The oral cancer ERK3 clone demonstrated 100% homology to human ERK3 isolated from fetal skeletal muscle, with four specific nucleotide alterations in the non-coding region of the gene, comprising deletion of 'TTT' between 2701 and 2705 nt; 'G' to 'T' substitution at 188 nt; insertion of 'A' between 121 and 122 nt, and insertion of 'CTTTA' between 3391 and 3392 nt. Southern analysis of EcoRI genomic digests indicated ERK3 specific fragments of 11, 8.6, 6.5 and 3.2 kb sizes. The mRNA transcript analysis defined a single transcript of 4.5 kb. RT-PCR analysis revealed a three- to eight-fold increase in ERK3 expression in a majority (90%) of oral cancer tissues and peripheral blood cells (61.5%) of the patients, whereas absence or low levels of expression was observed in peripheral blood cells of 74% clinically normal healthy individuals with no tobacco habits, and overexpression in PBC from 26% normal individuals. The alterations in the non-coding region of ERK3 gene cloned from oral cancer tissue, may affect stability or regulation of mRNA, resulting in overexpression in the patient samples. The overexpression of the gene in the normal healthy individuals may be indicative of increased risk of developing oral cancers in this group.

Characterization of Ngef, a novel member of the Dbl family of genes expressed predominantly in the caudate nucleus

We have identified Ngef as a novel member of the family of Dbl genes. Many members of this family have been shown to function as guanine nucleotide exchange factors for the Rho-type GTPases. Ngef is predominantly expressed in brain, with the strongest signal in the caudate nucleus, a region associated with the control of movement. Ngef contains a translated trinucleotide repeat, a polyglutamic acid stretch interrupted by a glycine. We have localized the Ngef gene to mouse chromosome 1 and the human homologue of Ngef to human chromosome 2q37. We have shown in preliminary experiments that Ngef has transforming potential in cell culture and is able to induce tumors in nude mice.

Microsatellite alterations on chromosome 9 in chewing tobacco-induced oral squamous cell carcinomas from India

Genomic instability as reflected by microsatellite alterations in specific target regions is an important characteristic of oral squamous cell carcinoma (OSCC). Microsatellite instability (MSI) and loss of heterozygosity (LOH) on chromosome 9 has been reported as an early event in oral cancers, primarily from patients in the USA and UK. Hence, we examined 77 primary oral cancer tissues and corresponding peripheral blood cell (PBC) DNA from Indian oral cancer patients for LOH and MSI, using a panel of 11 microsatellite markers spanning chromosome 9 on p and q arms. The patients were long-time (minimum 10 years) tobacco chewers. The matched DNA samples were amplified by polymerase chain reaction, resolved on a denaturing polyacrylamide gel and visualized by silver staining. An overall of 62% (48/77 cases) of the patients demonstrated microsatellite alterations including 27% MSI and 52% LOH, although at individual loci MSI was observed in 3-8% patients and LOH in the informative cases ranged from 4 to 41%. A majority of the alterations occurred on the p arm at 9p21-23, with 85% (41/48 cases) genetic alterations concentrated between markers D9S157 and D9S161. Multiple alterations were seen in 56% (27/48) of the affected cases with 17 patients showing microsatellite alterations in three to eight loci. Our data show the incidence of genetic alterations primarily in the chromosomal region 9p21-23, and may be indicative of involvement of p16 (CDKN2) tumor suppressor gene on chromosome 9p21, in a subset of chewing tobacco-induced oral cancers.

Immunolocalizaiton of c-Myc and bcl-2 proto-oncogene products in gingival hyperplasia induced by nifedipine and phenytoin

BACKGROUND

Hyperplastic gingival tissues show the histopathological characteristics of thick parakeratinized squamous epithelia with acanthosis and rete pegs elongated into the lamina propria. However, the pathogenic factors that contribute to the epithelial morphogenesis of this disease are obscure and remain to be studied.

METHODS

We immunohistochemically examined the expression of both c-Myc and bcl-2 oncoprotein, which can exert influence on the epithelial morphogenesis and homeostasis, in 12 hyperplastic gingival tissues induced by nifedipine and phenytoin as well as 5 control tissues using avidin-biotin-peroxidase complex methods.

RESULTS

Four specimens out of 5 nifedipine-induced and 5 out of 7 phenytoin-induced hyperplastic gingival tissues revealed the expression of c-Myc oncoprotein, whereas no significant immunostaining of c-Myc oncoprotein was found in 5 control tissues. The c-Myc oncoprotein-positive cells were observed to be localized in the basal and suprabasal cell layers of the hyperplastic gingival epithelia. Although all of the 12 hyperplastic gingival epithelia showed the distribution of bcl-2 oncoprotein in the basal and suprabasal layer cells, in 5 control epithelia the bcl-2 oncoprotein expression was slight and confined to the basal layer cells.

CONCLUSIONS

The results of our present study indicate that the synergistic overexpression of c-Myc and bcl-2 oncoprotein may be related to the pathogenesis of gingival hyperplasia induced by nifedipine and phenytoin, especially to the morphogenesis of hyperplastic epithelia.

Detection of HPV-16 genome in human oral cancers and potentially malignant lesions from India

The presence of high risk human papilloma virus (HPV) 16 and 18 was examined in 100 oral cancer patients of Indian descent, 80 patients with potentially malignant oral lesions and corresponding clinically normal mucosa from 48 of these patients. Additionally, presence of HPV-33, -6 and -11 was also studied in 86 oral cancers, 50 potentially malignant oral lesions and 30 corresponding normal oral mucosa. All the patients with oral cancer and oral lesions, were long term tobacco-chewers, and a majority of the patients were in Advanced Stages III and IV. The DNA samples were amplified by polymerase chain reaction (PCR) using HPV L1 consensus primers. Typing of HPV was performed by Southern hybridization analysis of the PCR products using HPV-16, -18, -33, -6 and -11 type specific oligonucleotide probes. HPV-16 was detected in 15 out of 100 (15%) oral tumours, 27 out of 80 (34%) potentially malignant lesions and 15 out of 48 (31%) of the corresponding normal mucosa in the patients with oral lesions. HPV-18 was not detected in any of the oral cancers, oral lesions and normal mucosa. HPV-33 and the low-risk HPV-6 and -11 were also not detected in the oral cancers, oral lesions and corresponding normal mucosa. A significantly higher prevalence of HPV-16 was observed in oral lesions (27 out of 80, 34%) as compared to oral cancers (15 out of 100, 15%). The observed difference of 19% (95% confidence interval [CI]: 6%, 31%), between these two proportions was statistically significant at the 5% level of significance. Our data indicates that HPV-16 may play a direct role in a certain proportion of oral cancers; whereas in a subpopulation of oral cancers HPV-16 infection may be vital in the early events associated with development of potentially malignant oral lesions, and the presence of the virus not essential in the progression of the oral lesion to frank malignancy.

Epstein-Barr virus in tobacco-induced oral cancers and oral lesions in patients from India

We examined 103 oral squamous cell carcinomas (OSCC), 100 oral lesions consisting primarily of leukoplakia (82 cases), and 76 clinically normal mucosa specimens from the contralateral site in the oral cavity of individuals with oral lesions, for the presence of Epstein-Barr virus (EBV). Polymerase chain reaction (PCR) was used to amplify a 239 bp fragment of the BamHIL region of the EBV genome, followed by Southern blot hybridization with EBV oligonucleotide probe to increase further the specificity and sensitivity of the assay system. Since EBV seropositivity is frequent in populations, we also examined the peripheral blood cells (PBC) from 141 patients (50 oral cancer patients, 91 patients with oral lesions) for the presence of EBV. We detected EBV in 25 of 103 (25%) OSCC, 13 of 100 (13%) oral lesions, 3 of 76 (4%) clinically normal mucosa samples and 10 of 141 (7%) PBC. Our results indicate that EBV may contribute as one of the multiple factors in oral cancers, in a certain proportion of Indian patients.