The role of p53 in death receptor-mediated apoptosis of testicular germ cells in response to mono-(2-ethylhexyl) phthalate treatment
Year: 2005
Type: dissertation
Abstract: Mono-(2-ethylhexyl) phthalate (MEHP) is the toxic metabolite of the common \nplasticizer di-(2-ethylhexyl) phthalate (DEHP). Exposure to DEHP or MEHP typically \nleads to testicular atrophy in laboratory animals. The prevalence of DEHP as an \nenvironmental contaminant is therefore cause for concern due to its potential to affect \nhuman testicular function and fertility. In the testis, MEHP induces the injury of the \nsupportive cells called Sertoli cells, leading to Fas death receptor-dependent apoptotic \nelimination of germ cells. This dissertation examines the molecular mechanisms that lead \nto this loss of germ cells resulting from testicular exposure to MEHP. The p53 tumor \nsuppressor protein is proposed as the cellular stress sensor that sensitizes specific germ \ncells to Fas-dependent cell death in response to the MEHP-induced Sertoli cell injury. \nThis is based upon recent reports that demonstrate p53’s ability to initiate the localization \n viii \nof Fas to the plasma membrane of cells in a transcription-independent manner, in addition \nto its ability to transcribe various pro-apoptotic proteins including Fas. \nIn experiments involving the exposure of pre-pubertal p53 wild-type and mutant \nmice (C57 x 129S/v) to a single oral dose of 1g MEHP /kg body weight, we were able to \ndemonstrate that mice lacking the p53 gene were partially protected from the testicular \ntoxicity induced by MEHP. These studies enabled us to establish that a lack of p53 \nexpression affected the activation of the Fas pathway in germ cells after MEHP exposure, \npartly by affecting Fas membrane localization and also by influencing the cellular \nretention of an inhibitor of this pathway, the c-FLIP (L) protein. To further clarify these \nresults, we examined the effect of Fas activation in GC-2spd (ts) cells, which are germ \ncells that demonstrate variable activation of p53 depending on the temperature that they \nare maintained at. The activation of the p53 protein increased the sensitivity of GC-2 \ncells to undergo Fas-mediated apoptosis by modulating Fas expression on the germ cell \nmembrane. Additionally, activation of Fas caused an increased tagging of c-FLIP (L) \nwith ubiquitin, indicating its targeting for degradation. Thus the p53 status of GC-2 cells \ninfluenced the membrane expression of Fas, subsequently influencing the degradation of \nthe anti-apoptotic protein c-FLIP (L). In summary, the results indicate that p53 promotes \nFas activated germ cell apoptosis in response to MEHP-induced Sertoli cell injury, by \ninstigating the degradation of c-FLIP (L) protein via its ubiquitinylation.
Author: Yamini Chandrasekaran
Language: English
Subfield: Health, Toxicology and Mutagenesis
Field: Environmental Science
Domain: Physical Sciences
Open Access status: green
OpenAlex ID: W1909873923