Proteasomal degradation of intracellularly expressed Amblyomin-X limits suicide gene therapy potential in melanoma cells.

Amblyomin-X is a complex Kunitz-type protease inhibitor from the tick Amblyomma sculptum, with selective pro-apoptotic effects in tumor cells. While promising when applied exogenously, its large-scale recombinant production is hindered by structural complexity. This study evaluated the feasibility of expressing Amblyomin-X via a suicide gene therapy approach and investigated its intracellular fate following gene delivery in human melanoma and nontumoral cell lines. Amblyomin-X transcripts were equally detected in both cell types; however, protein detection was restricted to nontumoral cells. Thus, we examined the mechanisms underlying Amblyomin-X degradation in melanoma cells. Mutagenesis of predicted ubiquitination/SUMOylation sites failed to restore protein detection, whereas inhibition of proteasome activity with MG132 restored Amblyomin-X detection. This confirmed the involvement of a proteasome-dependent mechanism that limits protein stability and consequently its cytotoxic activity when intracellularly produced in melanoma cells. These findings indicate that proteasomal degradation represents a tumor-specific barrier to the intracellular expression of Amblyomin-X in human cancer cells. Addressing this limitation could enable the potent activity of Amblyomin-X to be harnessed through gene-based anticancer strategies. Furthermore, these findings advance the understanding of how structurally complex Kunitz-type proteins with unstructured regions may behave in the context of gene therapy.