DOWN-REGULATION OF TSC-22 (TRANSFORMING-GROWTH-FACTOR BETA-STIMULATEDCLONE-22) MARKEDLY ENHANCES THE GROWTH OF A HUMAN SALIVARY-GLAND CANCER CELL-LINE IN-VITRO AND IN-VIVO

We have recently isolated TSC-22 (transforming growth factor beta-stim ulated clone 22) cDNA as a new anticancer drug (Vesnarinone)-inducible gene in a human salivary gland cancer cell line, TYS. We conducted th e present study to examine whether up-regulation or down-regulation of TSC-22 can affect the growth of TYS cells in vitro and in vivo. We co nstructed an expression vector containing sense-or antisense-oriented human TSC-22 cDNA under the transcriptional control of the SR alpha pr omoter. We cotransfected TYS cells with the sense or antisense express ion vector and pSV2neo and obtained more than 200 G418-resistant colon ies in each sense or antisense transfectant. Approximately 80% of repr esentative G418-resistant clones expressed the transcripts from transf ected sense or antisense TSC-22 cDNA. To avoid the clonal heterogeneit y of the cells, we mixed all of the G418-resistant colonies together i n each sense or antisense transfectant and examined the expression of TSC-22 protein, in vitro growth, and the tumorigenicity in nude mice. The expression of TSC-22 protein was examined by solid-phase ELISA usi ng a specific antibody against recombinant TSC-22 protein. The express ion of TSC-22 protein was up-regulated in the sense transfectants and down-regulated in the antisense transfectants. Contrary to our expecta tion, up-regulation of TSC-22 protein did not affect both in vitro and in vivo growth of TYS cells, However, do cvn-regulation of TSC-22 mar kedly enhanced the growth of TYS cells in vitro and in vivo., Furtherm ore, we examined the expression of TSC-22 mRNA in several human saliva ry gland tumors, The mRNA expression of TSC-22 in benign and malignant salivary gland tumors was significantly decreased when compared to th at in tumor-free salivary glands (P < 0.05; one-way ANOVA), and in som e salivary gland tumors, the expression of TSC-22 mRNA was not detecta ble by reverse transcription-PCR, These results suggest that down-regu lation of TSC-22 may play a major role on salivary gland tumorigenesis .