Mechanistic analysis of a dynamin effector.

Dynamin-related proteins (DRPs) can generate forces to remodel membranes. In cells, DRPs require additional proteins [DRP-associated proteins (DAPs)] to conduct their functions. To dissect the mechanistic role of a DAP, we used the yeast mitochondrial division machine as a model, which requires the DRP Dnm1, and two other proteins, Mdv1 and Fis1. Mdv1 played a postmitochondrial targeting role in division by specifically interacting and coassembling with the guanosine triphosphate-bound form of Dnm1. This regulated interaction nucleated and promoted the self-assembly of Dnm1 into helical structures, which drive membrane scission. The nucleation of DRP assembly probably represents a general regulatory strategy for this family of filament-forming proteins, similar to F-actin regulation.

The requirement for perp in postnatal viability and epithelial integrity reflects an intrinsic role in stratified epithelia.

Mice lacking the desmosome protein Perp exhibit blistering in their stratified epithelia and display postnatal lethality. However, it is unclear if these phenotypes are strictly related to Perp function in stratified epithelia, as Perp expression is not restricted to these tissues during embryogenesis, and certain desmosomal blistering diseases such as pemphigus vulgaris and pemphigus foliaceus have non-cell-intrinsic bases. Furthermore, we show here that Perp is expressed in the heart, raising the possibility that defects in heart function could account for lethality in the Perp-deficient mice. To determine conclusively if Perp function in stratified epithelia is crucial for postnatal survival and epithelial adhesion, we specifically ablated Perp in stratified epithelia by breeding conditional Perp knockout mice to keratin 5 (K5)-Cre transgenic mice. We found that the majority of mice lacking Perp in stratified epithelia die within 10 days after birth, accompanied by blistering and hyperproliferation in the epithelia, similar to the constitutive Perp null mice. Together, these findings indicate that Perp's requirement for both viability and epithelial integrity reflects a role in the stratified epithelial compartment.

Mice lacking the p53/p63 target gene Perp are resistant to papilloma development.

Perp is a target of the p53 tumor suppressor involved in the DNA damage-induced apoptosis pathway. In addition, Perp is a target of the p53-related transcription factor p63 during skin development, where it participates in cell-cell adhesion mediated through desmosomes. Here we test the role of Perp in tumorigenesis in a two-step skin carcinogenesis model system. We find that mice lacking Perp in the skin are resistant to papilloma development, displaying fewer and smaller papillomas than wild-type mice. Proliferation levels, apoptotic indices and differentiation patterns are similar in the skin of treated Perp-deficient and wild-type mice. Instead, impaired adhesion through aberrant desmosome assembly may explain the diminished tumor development in the absence of Perp. These studies indicate that in certain contexts, Perp is required for efficient carcinogenesis and suggest a role for intact cell-cell adhesion in supporting tumor development in these settings.

Perp is a p63-regulated gene essential for epithelial integrity.

p63 is a master regulator of stratified epithelial development that is both necessary and sufficient for specifying this multifaceted program. We show here that Perp, a tetraspan membrane protein originally identified as an apoptosis-associated target of the p53 tumor suppressor, is the first direct target of p63 clearly involved in mediating this developmental program in vivo. During embryogenesis, Perp is expressed in an epithelial pattern, and its expression depends on p63. Perp-/- mice die postnatally, with dramatic blistering in stratified epithelia symptomatic of compromised adhesion. Perp localizes specifically to desmosomes, adhesion junctions important for tissue integrity, and numerous structural defects in desmosomes are observed in Perp-deficient skin, suggesting a role for Perp in promoting the stable assembly of desmosomal adhesive complexes. These findings demonstrate that Perp is a key effector in the p63 developmental program, playing an essential role in an adhesion subprogram central to epithelial integrity and homeostasis.

Perp is a mediator of p53-dependent apoptosis in diverse cell types.

The induction of apoptosis by the p53 protein is critical for its activity as a tumor suppressor. Although it is clear that p53 induces apoptosis at least in part by direct transcriptional activation of target genes, the set of p53 target genes that mediate p53 function in apoptosis in vivo remains to be well defined. The Perp (p53 apoptosis effector related to PMP-22) gene is highly expressed in cells undergoing p53-dependent apoptosis as compared to cells undergoing p53-dependent G1 arrest. Perp is a direct p53 target, and its overexpression is sufficient to induce cell death in fibroblasts, implicating it as an important component of p53 apoptotic function. Here, through the generation of Perp-deficient mice, we analyze the role of Perp in the p53 apoptosis pathway in multiple primary cell types by comparing the cell death responses of Perp null cells to those of wild-type and p53 null cells. These experiments demonstrate the involvement of Perp in p53-mediated cell death in thymocytes and neurons but not in E1A-expressing MEFs, indicating a cell type-specific role for Perp in the p53 cell death pathway. In addition, we show that Perp is not required for proliferation-associated functions of p53. Thus, Perp selectively mediates the p53 apoptotic response, and the requirement for Perp is dictated by cellular context.