Prohibitin Family Members Interact Genetically with Mitochondrial Inheritance Components in Saccharomyces cerevisiae

Abstract

Phb2p, a homolog of the tumor suppressor protein prohibitin, was identified in a genetic screen for suppressors of the loss of Mdm12p, a mitochondrial outer membrane protein required for normal mitochondrial morphology and inheritance in Saccharomyces cerevisiae. Phb2p and its homolog, prohibitin (Phb1p), were localized to the mitochondrial inner membrane and characterized as integral membrane proteins which depend on each other for their stability. In otherwise wild-type genetic backgrounds, null mutations in PHB1 and PHB2 did not confer any obvious phenotypes. However, loss of function of either PHB1 or PHB2 in cells with mitochondrial DNA deleted led to altered mitochondrial morphology, and phb1 or phb2 mutations were synthetically lethal when combined with a mutation in any of three mitochondrial inheritance components of the mitochondrial outer membrane, Mdm12p, Mdm10p, and Mmm1p. These results provide the first evidence of a role for prohibitin in mitochondrial inheritance and in the regulation of mitochondrial morphology.Mitochondrial inheritance is an essential and active process by which daughter cells receive mitochondria prior to the completion of cytokinesis. In budding yeast, factors specifically required for mitochondrial inheritance have been identified and characterized through the analysis of conditional mutants (7,25). Three distinct proteins of the mitochondrial outer membrane, Mdm10p, Mmm1p, and Mdm12p, have been found to constitute one class of mitochondrial inheritance factors. Each protein is required for normal mitochondrial morphology and inheritance, and mdm10, mmm1, and mdm12 loss-of-function mutants exhibit similar phenotypes of temperature-sensitive growth and enlarged, round mitochondria (6, 9, 39). At least one of these proteins, Mdm12p, has been evolutionarily conserved and possesses a homolog in the fission yeast Schizosaccharomyces pombe (6). While the location of these proteins in the mitochondrial outer membrane suggests that they may interact with cytoskeletal elements to mediate normal mitochondrial distribution, their molecular activity remains to be defined.To explore Mdm12p function, high-copy-number plasmidborne suppressors able to bypass the cellular requirement for Mdm12p were identified. This paper describes the characterization of a plasmid-borne suppressor encoding a prohibitinrelated protein localized to the mitochondrial inner membrane and exhibiting genetic interactions with mitochondrial outer membrane inheritance components. Prohibitins are a family of conserved proteins whose first member was identified as a negative regulator of cell division in cultured animal cells (29). Prohibitin homologs have been identified in diverse organisms and cell types and have been localized to mitochondria in animal and plant cells (20,38). The function of prohibitin at the molecular level is unknown. MATERIALS AND METHODSStrains and media. The Saccharomyces cerevisiae strains used in this work are listed in Table 1. All strains were derived from MYY290 or MYY291 (37). Media fo...

The Mitochondrial Prohibitin Complex Is Essential for Embryonic Viability and Germline Function in Caenorhabditis elegans

“…These results are in agreement with observations in yeast, where the disruption of either phb gene leads to the loss of both proteins, although the mRNA for the intact gene can still be detected (4). As in yeast (4,6), the C. elegans PHB-1 and PHB-2 subunits are interdependent for assembly and protein stability. These results indicate that RNAi for both phb-1 and phb-2 genes is specific and effective.…”

“…Prohibitins (Phb1p and Phb2p), referred to here as PHB proteins, are evolutionarily strongly conserved proteins that are located in mitochondria in yeast, plants, and mammals (1)(2)(3)(4)(5)(6). In mammalian and yeast cells, it has been demonstrated that PHB proteins associate with each other to form a high molecular weight complex (the PHB complex) in the mitochondrial inner membrane (5,6).…”

Proteomics analysis of mitochondrial proteins reveals overexpression of a mitochondrial protein chaperon, prohibitin, in cells expressing hepatitis C virus core protein

“…as well as in the liver of core-gene transgenic mice. 7,8 Interestingly, Berger and Yaffe 31 showed that loss of function of prohibitin leads to an altered mitochondrial morphology, that is, the loss of the normal reticular morphology and organized mitochondrial distribution. In hepatocytes from the core-gene transgenic mice, we observed a change in morphology of mitochondria, a disappearance of the double structure of mitochondrial membranes.…”

Differential regulation of Rb family proteins and prohibitin during camptothecin-induced apoptosis

“…Indeed, increased prohibitin levels had no e ect on receptor-mediated apoptosis either. Thus, prohibitin is capable of speci®cally targeting certain pathways leading to apoptosis; it may be imagined that prohibitin is blocking some earlier, speci®c events rather than late, shared events common to all apoptotic pathways like disruption of mitochondrial integrity and release of cytochrome c. It is not known whether prohibitin can a ect these latter events in apoptosis, but it is an interesting possibility since prohibitin has been reported to be localized in the mitochondrial membranes as well (Coates et al, 2001;Nijtmans et al, 2000;Berger and Ya e, 1998;Steglich et al, 1999). Our experiments have shown prohibitin to be present ubiquitously in the cell, including the nucleus, where it co-localizes with Rb and a ects transcriptional activity of E2F (unpublished data).…”

“…It has been suggested that prohibitin associates with the IgM receptor in murine B lymphocytes (Terashima et al, 1994). In yeast, however, it has been found that prohibitin might associate with the mitochondrial inner membrane (Coates et al, 2001;Berger and Ya e, 1998;Steglich et al, 1999;Nijtmans et al, 2000). Most recently, prohibitin-2 was found to associate with and repress the nuclear estrogen receptor.…”