Rat HPC-1/syntaxin 1A and syntaxin 1B interrupt intracellular membrane transport and inhibit secretion of the extracellular matrix in embryonic cells of an amphibian.

HPC-1/syntaxin 1A and syntaxin 1B are proteins that have been implicated in the docking and/or fusion of synaptic vesicles to the presynaptic plasma membrane in neural cells. Capped RNAs (cRNAs) for rat HPC-1 and syntaxin 1B were injected into embryonic cells of an amphibian, the Japanese newt. The effects of the proteins translated from the injected cRNAs on intracellular membrane transport and secretion of the extracellular matrix (ECM) were then investigated. Immunoblotting and immunoelectron microscopy showed that the HPC-1 synthesized in the embryonic cells was localized on the membranes of Golgi complexes and vacuoles and on the plasma membrane. Electron microscopy revealed the morphological deformation of Golgi complexes, an appearance of large number of vacuoles, and the disappearance of the ECM from the cell surface in the cRNA-injected embryos. The results showed that HPC-1 and syntaxin 1B interrupt the pathways of intracellular membrane transport and inhibit the secretion of ECM by amphibian embryonic cells. Similar mechanisms may be involved in regulation of the secretory process of synaptic vesicles in mammalian neural cells and in regulation of intracellular membrane transport and constitutive secretion of ECM in amphibian embryonic cells.