Recurrent copy number gain of transcription factor SOX2 and corresponding high protein expression in oral squamous cell carcinoma

Abstract

Gene copy number aberrations are involved in oral squamous cell carcinoma (OSCC) development. To delineate candidate genes inside critical chromosomal regions, array-CGH was applied to 40 OSCC specimens using a microarray covering the whole human genome with an average resolution of 1 Mb. Gene copy number gains were predominantly found at 1q23 (9 cases), 3q26 (11), 5p15 (13), 7p11 (7), 8q24 (17), 11q13 (15), 14q32 (8), 19p13 (8), 19q12 (7), 19q13 (8), and 20q13 (9), whereas gene copy number losses were detected at 3p21-3p12 (15), 8p32 (11), 10p12 (8), and 18q21-q23 (10). Subsequent mRNA expression analyses by quantitative real time polymerase chain reaction found high mRNA expression of candidate genes SOX2 in 3q26.33, FSLT3 in 19p13.3, and CCNE1 in 19q12. Tissue microarray (TMA) analyses in a representative OSCC collection found gene copy number gain for SOX2 in 52% (115/223) and for CCNE1 in 31% (72/233) of the tumors. Immunohistochemical analyses on TMA sections of the corresponding proteins detected high expression of SOX2 in 18.1% (49/271) and of CyclinE1 in 23.3% (64/275) of tumors analyzed. These findings indicate that SOX2 and CCNE1 might be activated via gene copy number gain and participate in oral carcinogenesis. The combination of array-CGH with TMA analyses allows rapid pinpointing of novel promising candidate genes, which might be used as therapeutic stratification markers or target molecules for therapeutic interference.

Comparative expressed sequence hybridization detects recurrent patterns of altered sequence expression in oral squamous cell carcinoma

“…Further chromosome regions of recurrent high mRNA expression detected in the present study are 14q32 and 22q13, for which DNA copy number gain has been found in previous studies in OSCC (25)(26)(27). These findings underline the assumption that high mRNA expression levels detected by CESH reflect an increase in gene transcription, which is frequently the result of distinct DNA copy number gain.…”

“…The proto-oncogene CCNE1 is located at 19q12, it is a member of the cyclin family, which has been shown to play an important role in G1/S transition of the cell cycle. Gene copy number gain of the CCNE1 locus and high cyclin E1 protein expression was found in about 25% of OSCC cases analyzed suggesting an activation of CCNE1 by gene copy number gain (25). According to our CESH data, the most frequent high mRNA expression is found on the distal chromosome bands 19q13.1-19q13.2.…”

“…In chromosomal comparative genomic (cCGH) analysis, the evaluation of chromosome 19 hybridization signals was considered to be critical due to a large amount of GC-rich DNA sequences (24). In recent array-CGH analyses, however, distinct regions of frequent DNA copy number gain were found on chromosome 19, including 19q12 and 19q13.12 (25). The proto-oncogene CCNE1 is located at 19q12, it is a member of the cyclin family, which has been shown to play an important role in G1/S transition of the cell cycle.…”

SOX2 gene amplification and protein overexpression are associated with better outcome in squamous cell lung cancer

“…9,15,25 Besides the lung, SOX2 has been found to be amplified and expressed in squamous cell carcinomas originating from other organ sites, predominantly derived from the embryonic foregut. 9,21,22 Recently, we found SOX2 to be amplified and expressed in squamous cell carcinomas originating from non-foregut tissues, such as the skin, the cervix, and the penis, 23 indicating that SOX2 might be a general marker for squamous cell carcinoma differentiation regardless the tissue of origin. Squamous carcinogenesis from diverse body sites may thus share similar underlying mechanisms.…”

“…17,20 SOX2 may have similar oncogenic effects in other organs of foregut and non-foregut origin, since amplification and expression also occur in squamous cell carcinomas of the oral cavity, as well as in esophageal and gastric tumors. 9,[21][22][23] Recently, SOX2 expression has been detected in early-stage breast carcinoma. 24 These data suggest that expression of SOX2 drives oncogenesis and therefore overexpression in tumors may be associated with a more aggressive tumor phenotype and poorer clinical outcome.…”