Microcystins (MCs) are important cyclic heptapeptide hepatotoxicins due to their acute toxicity and potent tumor-promoting activity.Microcystins are usually delivered into cells by organic anion transporting peptides (OATPs) where they mainly target PP2A and partially target PP1.Endo-Porter (EP), a peptide reagent that binds to the cell membrane, could be instead of OATPs to transport microcystin-LR (MCLR) into cells.In the present study, human amnion epithelia cells (FL cells) were used as a model to perform the comparison of cytotoxicity of MCLR in the presence and absence of ER In the presence of EP, an obvious accumulation of MCLR in FL cells was detected by western blot and immunofluorescence in addition to a marked inhibition of PP2A activity.Apoptosis was also evident in the EP-treated MCLR group.Moreover, ERK1/2, JNK, and p38 were activated in the EP-treated group and time-dependent MEK1/2-ERK1/2 activation further confirmed activation of the ERK pathway.These results highlight the utility of the transporter EP for investigating the toxicity of MCs in FL cells.