2 ACTIVE COPIES OF THE X-LINKED GENE SPERMIDINE SPERMINE N-1-ACETYLTRANSFERASE (SSAT) IN A FEMALE LUNG-CANCER CELL-LINE ARE ASSOCIATED WITHAN INCREASE IN SENSITIVITY TO AN ANTITUMOR POLYAMINE ANALOG/

The expression of the polyamine catabolic enzyme, spermidine/spermine N-1-acetyltransferase (SSAT), has been associated with tumor sensitivi ty to antitumor polyamine analogues. In the sensitive cell types the l evel of SSAT is greatly induced by these agents. Although SSAT express ion is regulated at many levels, the initial regulation of this X-link ed gene occurs at the level of transcription. Because most previous wo rk in human cell lines has been performed in cells of male origin and because the SSAT gene is located near the pseudoautosomal region of th e X chromosome, we investigated the possibility that both copies of SS AT could be expressed in normal and tumor cells in women. DNA methyl-s ensitive restriction enzyme analysis of DNA from normal peripheral lym phocytes suggested that like most X-linked genes, only one copy of SSA T is actively transcribed, However, in an examination of four represen tative human lung tumor cell lines derived from women, two were found to have a methylation pattern identical to male-derived cells, suggest ing a reactivation of the normally inactive allele or loss of the inac tive allele, Microsatellite repeat polymorphism analysis indicated tha t one of the lines, a female carcinoid line, NCI H727, had reactivated the previously inactive copy, thus providing H727 with two active all eles, whereas a small cell lung cancer line, H889, appears to have los t the inactive allele, Most importantly, the H727 line expressed high amounts of SSAT mRNA and protein in response to treatment with the pol yamine analogue, N-1,N-12-bis(ethyl)spermine, a compound known to incr ease SSAT transcription in sensitive cell types. H727 was also the onl y female line that responded to treatment in a cytotoxic manner, These data suggest that both copies of the SSAT allele may be expressed and that the inappropriate expression of the second copy can lead to an i ncrease in tumor sensitivity to polyamine analogues that induce SSAT.