Effects of retinoic acid on the expression of a tumor rejection antigen (heat shock protein gp96) in human cervical cancer

Retinoids are a class of compounds structurally related to vitamin A which have been found to be active agents experimentally as well as clinically in the prevention and treatment of cervical cancer. Recent data have suggested that in addition to their key regu latory role during epithelial cell differentiation, they could also contribute to enhanced cellular and humor-al immunity against tumor cells. Hsp gp96 molecules have recently been implicated in the presentation of tumor and viral antigens. A number of key elements in this pathway, including major histocompatibility complex (MHC) class I molecules as well as adhesion/co-stimulation molecules such as ICAM-I have reported to be sensitive to retinoic acid up-regulation. In this study we analyzed at the transcriptional (Northern blot) and post-transcriptional levels (Western blot) the effects of retinoic acid on the expression of the tumor-rejection antigen (heat shock protein gp96) in three human cervical carcinoma cell lines. Exposure of therapeutic doses of retinoic acid (i.e. 1 mu M) significantly and consistently increased the expression of heat shock protein gp96 (Western blot analysis) on CaSki, SiHa and HT-3 cervical cancer cell lines. Northern blot analysis demonstrated that the increase in the amount of protein was due to the transcriptional upregulation of this gene. Taken together, our results show that retinoic acid can significantly increase the expression of yet another immunologically important cell molecule, the tumor rejection antigen heat shock protein gp96 in human cervical cancer. Such findings provide new information on the effects of retinoic acid on tumor cells and further support the role of retinoic acid as a powerful biologic response modifier.