Suppression of c-myc mRNA expression by steroid hormones in HTLV-I-infected T-cell line, KH-2

The effects of 1,25(OH)2D3 and dexamethasone on cellular proliferation and gene expression of the HTLV-I-infected T-cell line, KH-2, established from a patient with adult T-cell leukemia, endemic in the south-west Japanese islands and the Caribbean, were examined. KH-2 cells are integrated by HTLV-I proviral DNA and expressed mRNA for c-myc, IL-2 receptor alpha-chain (IL-2R alpha), and T-cell receptor beta-chain (TCR beta) while it did not express IL-2 mRNA. 1,25(OH)2D3 and dexamethasone did not suppress the mRNA levels of HTLV-I, IL-2R alpha or TCR beta but reduced the c-myc mRNA level. The reduction of c-myc mRNA level was marked in 1,25(OH)2D3-treated cells but relatively weak in dexamethasone-treated cells. This inhibitory effect of the steroid hormones correlated with the inhibition of KH-2 cell proliferation.