Human oral cancers have altered expression of Bcl-2 family members and increased expression of the anti-apoptotic splice variant of Mcl-1.
Expression of Bcl-2 family proteins in tumours can modulate apoptosis, influencing tumour behaviour and treatment. To investigate their role in oral tumourigenesis, nine Bcl-2 family transcripts were examined in three oral cell lines and 25 oral tumours, using ribonuclease protection assay. Since Mcl-1 mRNA was elevated in these samples, Mcl-1 splice variants were assessed by RT-PCR and Mcl-1 protein was studied in normal, premalignant and malignant oral tissues and cell lines, by immunohistochemistry and/or immunoblotting. The cell lines exhibited significantly higher levels of 7/9 Bcl-2 family transcripts as compared to those in normal tongue, and significantly higher (p=0.030, p=0.004) anti-apoptotic versus pro-apoptotic transcripts. Elevated Mcl-1 mRNA was observed in 11/25 (44%) tumours as compared to normal tissues with a five- to ten-fold higher expression of full-length anti-apoptotic Mcl-1 transcript versus the pro-apoptotic short isoform. Strong cytoplasmic Mcl-1 immunoreactivity was detected predominantly in differentiated epithelia in 27/33 (82%) oral tumours, 18/20 (90%) leukoplakia, 25/30 (83%) submucous fibrosis and 3/3 oral cell lines, with weak staining in 8/15 (53%) normal mucosa samples. Mcl-1 positivity in malignant and premalignant tissues was comparable but significantly higher (p<0.01) than that in normal mucosa. The expression of bcl-2 family genes, including Mcl-1 in tumours, did not correlate significantly with clinicopathological parameters. This is the first report delineating the in vivo expression patterns of Mcl-1 protein and Mcl-1 transcripts in oral cancers and premalignant lesions. The observed imbalance between expression of anti-apoptotic and pro-apoptotic Bcl-2 family genes may promote survival in the oral cell lines. Since the majority of oral tumours associated with tobacco-chewing evolve from premalignant lesions, the sustained expression of full-length anti-apoptotic Mcl-1 protein in these tissues suggests an important role for Mcl-1, early in oral cancer pathogenesis in protecting cells from apoptosis via neutralization of pro-apoptotic members and could be a potential therapeutic target for oral cancers.
Mallick
S
S
Advanced Centre for Treatment, Research and Education in Cancer, Kharghar, Navi Mumbai-410210, India.
Patil
R
R
Gyanchandani
R
R
Pawar
S
S
Palve
V
V
Kannan
S
S
Pathak
K A
KA
Choudhary
M
M
Teni
T R
TR
D000704:Analysis of Variance; D017209:Apoptosis / Q000235:genetics; D002294:Carcinoma, Squamous Cell / Q000235:genetics*; D045744:Cell Line, Tumor; D005260:Female; D015870:Gene Expression; D015972:Gene Expression Regulation, Neoplastic; D019254:Genes, bcl-2; D006801:Humans; D007150:Immunohistochemistry; D007971:Leukoplakia / Q000378:metabolism; D008297:Male; D008875:Middle Aged; D009061:Mouth Mucosa / Q000737:chemistry; D009062:Mouth Neoplasms / Q000235:genetics*; D064549:Myeloid Cell Leukemia Sequence 1 Protein; D020033:Protein Isoforms / Q000032:analysis / Q000235:genetics*; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000032:analysis / Q000235:genetics*; D012333:RNA, Messenger / Q000032:analysis; D020133:Reverse Transcriptase Polymerase Chain Reaction; D014059:Tongue / Q000378:metabolism
D064549:Myeloid Cell Leukemia Sequence 1 Protein; D020033:Protein Isoforms; D019253:Proto-Oncogene Proteins c-bcl-2; D012333:RNA, Messenger