Cross-talk between the Akt and NF-κB Signaling Pathways Inhibits MEHP-Induced Germ Cell Apoptosis

Abstract

Phthalates are ubiquitous contaminants that target the testis during in utero and postnatal development. The PI3K/Akt and nuclear factor kappa B (NF-kappaB) signaling pathways have been implicated in germ cell survival following testicular injury. Here we observe that Akt kinase activity increases in the testes of postnatal day 28 wild-type mice following exposure to 500 mg/kg mono-(2-ethylhexyl) phthalate (MEHP), and that loss of Akt1 results in the premature onset of germ cell apoptosis. To further determine the basis for this sensitivity, we investigated the potential for cross-talk between the PI3K/Akt and NF-kappaB signaling pathways. We found a twofold increase in Akt1-dependent phosphorylation of the I kappaB alpha subunit following exposure to 500 mg/kg MEHP and decreased levels of the total I kappaB alpha protein. Examination of the expression of the NF-kappaB subunits, p50 and p65, in Akt1 wild-type testes following MEHP exposure revealed a twofold increase in p50 mRNA at 6 h. Interestingly, in Akt1-deficient testes, basal expression of both the p50 and p65 subunits was elevated 1.6- and 4-fold, respectively. This was due, at least in part, to increased levels of oxidative stress as measured by both superoxide anion formation and increased expression of SMAC/DIABLO, a proapoptotic mitochondrial protein. In wild-type testes, MEHP-induced Akt1-dependent transcription of the antiapoptotic mitochondrial target gene, Bcl-xL. Together, these results indicate that Akt1 plays a role in the initial protection of germ cells following MEHP-induced germ cell apoptosis and that this response is partially mediated by cross-talk with the NF-kappaB signaling pathway and an increased sensitivity to oxidative stress.

Herbal compound triptolide synergistically enhanced antitumor activity of amino-terminal fragment of urokinase

“…Indeed, combined treatment with TPL and ATF significantly decreased the expression of c-FLIP, a well-known anti-apoptotic protein, and finally led to cell apoptosis. It has been reported that the ser/thr kinase AKT can promote NF-κB activity [31,32]. In the current study, we found that TPL and ATF combined treatment did not affect the total expression of AKT, but significantly decreased the phosphorylation level of AKT (Figure 4B).…”

“…Western blotting analysis revealed that siRNA against NF-κB p65 effectively reduced NF-κB/p65 and c-FLIP-L levels in the transfected cells (Figure 4C). AKT was reported to suppress apoptosis by stimulating the transactivation potential of the RelA/p65 subunit of NF-κB [31,32]. Therefore, the detection of Ser473 p-AKT and total AKT in HCT116 cells was performed following exposure to TPL and ATF for 24 h. Figure 4B revealed that the phosphorylation level of AKT was markedly decreased after co-treatment with TPL and ATF, but not either drug alone.…”

Akt1 protects against germ cell apoptosis in the postnatal mouse testis following lactational exposure to 6-N-propylthiouracil

“…As has been previously reported by ourselves (28, 29) and others (30, 31), Akt1 deficiency results in smaller overall body size (Table 2). At postnatal day 15, PTU exposure did not significantly alter body weight in any genotype examined.…”

Di (2-ethylhexyl) phthalate inhibits growth of mouse ovarian antral follicles through an oxidative stress pathway

“…In mouse allergic effector cells, DEHP increases AP-1 transcriptional activation via p38 MAPK phosphorylation (Oh and Lim, 2010). Further, mono- (2-ethylhexyl) phthalate (MEHP), the active metabolite of DEHP, also activates NF-κB signaling in the rat testis and induces germ cell apoptosis (Rasoulpour and Boekelheide, 2005; Rogers et al , 2008). Thus, it is quite possible that DEHP alters the expression of Sod1 through any of these pathways.…”