α-Actinin-containing branched microvilli isolated from an ascites adenocarcinoma

Microvilli, slender projections approximately 0.1 micrometer in diameter which occur on the surfaces of many cell types, are bounded by plasma membrane except at the site of attachment to the cell body and contain microfilament bundle cores. The presence of both microfilaments and plasma membrane suggests the use of microbilli for investigations of membrane cytoskeleton interactions. Immunofluorescence studies with anti-alpha-actinin have suggested that alpha-actinin is concentrated at the tips of intestinal brush border microvilli and might link actin microfilaments and the plasma membrane. However, this idea was disputed by later immunofluorescence and electrophoresis studies. To investigate the components and organization of microvilli from a less highly differentiated cell type, we have used an ascites sub-line (MAT-Cl) of a rat mammary tumour, the 13762 mammary adenocarcinoma, whose microvilli are high branched. Becaused such unusual structures may provide an understanding of cell-surface assemblies important in determining cell morphology, we have developed a procedure for isolating the branched microvilli and have shown that they contain significant quantities of alpha-actinin

The Effects of IRE1, ATF6, and PERK Signaling on adRP-Linked Rhodopsins

Many mutations in rhodopsin gene linked to retinitis pigmentosa (RP) cause rhodopsin misfolding. Rod photoreceptor cells expressing misfolded rhodopsin eventually die. Identifying mechanisms to prevent rhodopsin misfolding or to remove irreparably misfolded rhodopsin could provide new therapeutic strategies. IRE1, ATF6, and PERK signaling pathways, collectively called the unfolded protein response (UPR), regulate the functions of endoplasmic reticulum, responsible for accurate folding of membrane proteins such as rhodopsin. We used chemical and genetic approaches to selectively activate IRE1, ATF6, or PERK signaling pathways one at a time and analyzed their effects on mutant rhodopsin linked to RP. We found that both artificial IRE1 and ATF6 signaling promoted the degradation of mutant rhodopsin with lesser effects on wild-type rhodopsin. Furthermore, IRE1 and ATF6 signaling preferentially reduced levels of aggregated rhodopsins. By contrast, PERK signaling reduced levels of wild-type and mutant rhodopsin. These studies indicate that activation of either IRE1, ATF6, or PERK prevents mutant rhodopsin from accumulating in the cells. In addition, activation of IRE1 or ATF6 can selectively remove aggregated or mutant rhodopsin from the cells and may be useful in treating RP associated with rhodopsin protein misfolding