Aberrant expression of serpin squamous cell carcinoma antigen 2 in human tumor tissues and cell lines: evidence of protection from tumor necrosis factor-mediated apoptosis.

Squamous cell carcinoma antigens (SCCA) 1 and 2 are highly homologous proteins of the serpin family, although they inhibit different types of proteinases. We investigated the expression of both SCCA mRNAs in tumor tissues, in various cell lines (A431, SAS, Ca9, HeLa, SKGIIIa, HSC-2, HSC-3, HSC-4 and KB) and in HSC cell lines in the presence of tumor necrosis factor-alpha (TNF-alpha). The expression of SCCA2 mRNA could be differentiated from that of SCCA1 in tumor tissues and cell lines by means of reverse transcription-polymerase chain reaction (RT-PCR). The ratio between SCCA1 and SCCA2 mRNA expression showed selective expression of SCCA2 mRNA in SCC tissues from the uterine cervix compared to SCC tissues from the esophagus or skin. In addition, a significant level of SCCA2 mRNA expression was detected in the HSC-4 cell line, but not in Ca9, HeLa, SKG-IIIa, or HSC-3 cells. In contrast, SCCA1 mRNA was detected in all samples tested. These results suggest that the level of expression of SCCA2 mRNA detected by RT-PCR can be used to evaluate the status of SCC tumors. Next, we studied the effect of TNF-alpha on SCCA1 and SCCA2 mRNA expression in HSC cell lines. SCCA1 mRNA expression was constantly increased in the three HSC cells examined with increasing time of exposure to TNF-alpha. In contrast, SCCA2 mRNA expression was specific for HSC-4 cells. The survival rate of HSC-4 cells pretreated with TNF-alpha (6.3 ng/ml) for 48 h was found to be 72%, compared with 42% and 9% for HSC-3 and HSC-2 cells, respectively, after apoptotic stimulation by TNF-alpha (10 ng/ml) and cycloheximide (10 microg/ml) for 18 h. Furthermore, selective expression of SCCA2 mRNA in HSC-4 pretreated with TNF-alpha protected these cells from TNF-alpha-mediated apoptosis. Thus, SCCA2 overexpression in squamous tumor cells contributed to their survival by protecting them against TNF-alpha-induced apoptosis.