Complex regulation of prothymosin alpha in mammary tumors arising in transgenic mice

Expression of prothymosin alpha (PTA) has been related to cell proliferatio n, both normal and pathological. PTA has also been proposed to be a target of the c-myc protooncogene. To study PTA mRNA levels during pathological ce ll growth, and especially the effect of the activation of specific oncogene s on PTA expression, we have studied its expression in tumors that arise in transgenic mice. We found high PTA levels in mammary tumors arising in c-m yc, c-neu, and v-ras transgenic mice. Levels of this protein were variable between different tumors, and there is a differential regulation of PTA res pect to other putative c-myc target genes, such as Ornithine Decarboxylase (ODC). Furthermore, expression of PTA is not absolutely dependent of c-myc expression, as shown by MYC depletion experiments performed with antisense oligonucleotides. We conclude that regulation of PTA in these tumors is com plex and depends on more than a single activated oncogene.