Transformation-defective adenovirus 5 E1A mutants exhibit antioncogenic properties in human BLM melanoma cells

Abstract

Adenoviral E1A proteins exhibit a strong tumor-suppressive activity in human tumor cells. However, E1A is capable of transforming rodent and human cells in cooperation with other oncoproteins, such as activated RAS. Thus, the therapeutic use of wild-type E1A harbors the principal risk of enhancing tumor malignancy. This prompted us to construct E1A 13S cDNA-derived mutants that were unable to transform baby mouse kidney cells in cooperation with E1B and to test their tumor-suppressive activity in BLM human melanoma cells. Anchorage-independent growth in soft agar was reduced for those cell lines expressing the E1A_delCR2 mutant, which lacks the entire conserved region 2 (CR2) sequences, or for cells expressing the E1A_CR3Ex2 mutant, which contains CR3 plus exon 2 sequences. In contrast, cell lines expressing the entire E1A wild-type (E1A_WT) or only the exon 2 sequences (E1A_Ex2) grew like the parental BLM cells. Moreover, inoculation of nude mice with BLM cells or cells expressing E1A_Ex2 revealed large tumors after 2 weeks. In contrast, tumors derived from E1A_delCR2- or E1A_CR3Ex2-expressing cells exhibited a substantial delay in tumor growth accompanied by a loss of E1A expression in the outgrown tumors. Cell lines expressing E1A_WT showed an intermediate phenotype. Thus, expression of CR3 plus exon 2 sequences is sufficient to enhance both the antioncogenic properties and the therapeutic safety of E1A in our system.