Actin cytoskeleton and budding pattern are altered in the yeast rvs161 mutant: the Rvs161 protein shares common domains with the brain protein amphiphysin

Abstract

The actin cytoskeleton cells is altered in rvs161 mutant yeast, with the defect becoming more pronounced under unfavorable growth conditions, as described for the rvs167 mutant. The cytoskeletal alteration has no apparent effect on invertase secretion and polarized growth. Mutations in RVS161, just as in RVS167, lead to a random budding pattern in a/alpha diploid cells. This behavior is not observed in a/a diploid cells homozygous for the rvs161-1 or rvs167-1 mutations. In addition, sequence comparisons revealed that amphiphysin, a protein first found in synaptic vesicles of chicken and shown to be the autoantigen of Stiff Man syndrome, presents similarity with both Rvs proteins. Furthermore, limited similarities with myosin heavy chain and tropomyosin alpha chain from higher eukaryotic cells allow for the definition of a possible consensus sequence. The finding of related sequences suggests the existence of a function for these proteins that is conserved among eukaryotic organisms.

A role of amphiphysin in synaptic vesicle endocytosis suggested by its binding to dynamin in nerve terminals.

“…The two yeast proteins are hypothesized to form heterodimers, as mutations in the RVS161 and RVS167 genes produce a similar phenotype and are suppressed by the same set of genes (35,36). The mutant phenotype includes a striking endocytic defect (36) in addition to growth and polarity defects (34,35,37). The endocytic defect is characterized by impaired membrane internalization from the cell surface with a block of Lucifer yellow uptake and a major impairment of a-factor receptor internalization (36).…”

Clathrin interacts specifically with amphiphysin and is displaced by dynamin1

“…When this domain is microinjected into the lamprey synapse [7], or transfected into fibroblasts [8], a potent block in clathrin-mediated endocytosis is observed. Mutations in the Rvs yeast homologues [9][10][11][12][13] and studies of the neurological side effects of autoimmunity against amphiphysin in Stiff Man's syndrome [11] also support a role for amphiphysin in endocytosis.…”

Mechanisms of apoptosis by c-Myc

“…If Bin1 has endocytotic roles outside neurons, given the links of c-Myc to CD95/Fas and TNF-R, it is tempting to speculate about connections to mechanisms used by p53 to control apoptosis by cell surface tra cking of CD95/Fas (Bennett et al, 1998), or to potential requirements of CD95/Fas internalization via endocytosis for the generation of a competent death signal (A Ashkenazi, personal communication). Third, the orthologs of Bin1 in yeast can in¯uence cytoskeletal regulation and interact with a functionally unde®ned transmembrane protein (Sivadon et al, 1995(Sivadon et al, , 1997Breton and Aigle, 1998). These roles hint of links to cell surface receptors and perhaps also to actin cytoskeletal rearrangements that are involved in membrane blebbing (zeosis), a process which has been reported to involve integrins, actin depolymerization, and Jnk activation events (Laster and Mackenzie, 1996;Huot et al, 1998).…”