Phorbol esters promote postsynaptic accumulation of Vesl-1S/Homer-1a protein

We examined effects of phorbol esters on the amount and the subcellular dis tribution of the activity-regulated protein Vesl-1S/ Homer-la in cultured h ippocampal neurons. Major Vesl-1S immunoreactivity (IR) was detected throug hout neuronal somata under control conditions. Bath application of phorbol esters, PMA and PDBU resulted in the increase in the amount of Vesl-1S prot eins and promoted punctate distribution of Vesl-1S IR at the cortical regio ns of the neuronal somata. Immunofluorescent observations using antisynapto physin and anti-Vesl-1S antibodies, and electron microscopic observations, revealed that Vesl-1S accumulated at postsynaptic regions following PMA app lication. Membrane depolarization with high concentrations of external pota ssium also promoted the punctate distribution of Vesl-1S IR. These results demonstrate that phorbol-triggered reaction cascades result in the accumula tion of Ves-1S protein at postsynaptic regions, and suggest that these phor bol effects may mimic those caused by synaptic activities.