THE AMF-R TUBULE IS A SMOOTH ILIMAQUINONE-SENSITIVE SUBDOMAIN OF THE ENDOPLASMIC-RETICULUM

Autocrine motility factor receptor (AMF-R) is a marker for a distinct smooth membranous tubule, Ilimaquinone (IQ) is a sea sponge metabolite which induces the complete vesiculation of the Golgi apparatus and we show here that the addition of IQ to MDCK cells also results in the d isruption of the AM[F-R tubule. By immunofluorescence microscopy, the resultant punctate AMF-R label resembles the products of IQ-mediated v esiculation of the trans-Golgi network, however, the two labels can be distinguished by confocal microscopy, AMF-R tubule fragmentation occu rs after nocodazole or taxol treatment of the cells demonstrating that the action of IQ on AMF-R tubules is not related to the ability of IQ to depolymerize microtubules, IQ activity is therefore not Golgi-spec ific, Electron microscopy of IQ-treated cells reveals that AMF-R is di stributed to fenestrated networks of narrow interconnected tubules whi ch are distinguishable from the uniform Golgi-derived vesicles and mor phologically equivalent to smooth ER, Distinct fenestrations are visib le in incompletely fragmented tubules which may represent intermediate s in the fragmentation ]process. Smooth AMF-R labeled tubules exhibit continuity with rough ER cisternae and IQ selectively targets smooth a nd not rough ER, AMF-R tubules can be distinguished from the intermedi ate compartment labeled for ERGIC-53 by confocal microscopy and thus c onstitute a distinct IQ-sensitive subdomain of the smooth ER.