Sam D Stephen

Publications (2) View all

• Article: Hexavalent chromium-induced apoptosis of granulosa cells involves selective sub-cellular translocation of Bcl-2 members, ERK1/2 and p53.

  Sakhila K Banu, Jone A Stanley, Jehoon Lee, Sam D Stephen, Joe A Arosh, Patricia B Hoyer, Robert C Burghardt
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  ABSTRACT: Hexavalent chromium (CrVI) has been widely used in industries throughout the world. Increased usage of CrVI and atmospheric emission of CrVI from catalytic converters of automobiles, and its improper disposal causes various health hazards including female infertility. Recently we have reported that lactational exposure to CrVI induced a delay/arrest in follicular development at the secondary follicular stage. In order to investigate the underlying mechanism, primary cultures of rat granulosa cells were treated with 10 μM potassium dichromate (CrVI) for 12 and 24h, with or without vitamin C pre-treatment for 24h. The effects of CrVI on intrinsic apoptotic pathway(s) were investigated. Our data indicated that CrVI: (i) induced DNA fragmentation and increased apoptosis, (ii) increased cytochrome c release from the mitochondria to cytosol, (iii) downregulated anti-apoptotic Bcl-2, Bcl-XL, HSP70 and HSP90; upregulated pro-apoptotic BAX and BAD, (iv) altered translocation of Bcl-2, Bcl-XL, BAX, BAD, HSP70 and HSP90 to the mitochondria, (v) upregulated p-ERK and p-JNK, and selectively translocated p-ERK to the mitochondria and nucleus, (vi) activated caspase-3 and PARP, and (vii) increased phosphorylation of p53 at ser-6, ser-9, ser-15, ser-20, ser-37, ser-46 and ser-392, increased p53 transcriptional activation, and downregulated MDM-2. Vitamin C pre-treatment mitigated CrVI effects on apoptosis and related pathways. Our study, for the first time provides a clear insight into the effect of CrVI on multiple pathways that lead to apoptosis of granulosa cells which could be mitigated by vitamin C.
  Toxicology and Applied Pharmacology 01/2011; 251(3):253-66. · 4.45 Impact Factor
• Article: Interferon tau regulates PGF2alpha release from the ovine endometrial epithelial cells via activation of novel JAK/EGFR/ERK/EGR-1 pathways.

  Sakhila K Banu, JeHoon Lee, Sam D Stephen, Thamizh K Nithy, Joe A Arosh
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  ABSTRACT: In ruminants, pulsatile release of prostaglandin F2α (PGF(2α)) from the endometrium is transported to the ovary and induces luteolysis thereby allowing new estrous cycle. Interferon tau (IFNT), a type 1 IFN secreted by the trophoblast cells of the developing conceptus, acts on endometrial luminal epithelial (LE) cells and inhibits pulsatile release of PGF(2α) and establishes pregnancy. One of the unknown mechanisms is that endometrial pulsatile release of PGF(2α) is inhibited whereas basal release of PGF(2α) is increased in pregnant compared with nonpregnant sheep. We have recently found that pulsatile release of PGF(2α) from the endometrium is regulated by prostaglandin transporter (PGT)-mediated mechanisms. We hypothesize that modulation in the endometrial pulsatile vs. basal release of PGF(2α) likely requires PGT-mediated selective transport, and IFNT interacts with PGT protein and modulates pulsatile vs. basal release of PGF(2α). The new findings of the present study are: 1) IFNT activates novel JAK-SRC kinase-EGFR-RAS-RAF-ERK1/2-early growth response (EGR)-1 signaling module in LE cells; 2) IFNT increases interactions between PGT and ERK1/2 or EGR-1 proteins and alters phosphorylation of PGT protein; 3) IFNT precludes action of protein kinase C and Ca(2+) on PGT function; and 4) IFNT inhibits 80% PGT-mediated but not 20% simple diffusion-mediated release of PGF(2α) from the endometrial LE cells through this novel signaling module. The results of the present study provide important new insights on IFNT signaling and molecular control of PGT-mediated release of PGF(2α) and unravel the underlying mechanisms responsible for the increased basal release of PGF(2α) at the time of establishment of pregnancy in ruminants.
  Molecular Endocrinology 10/2010; 24(12):2315-30. · 4.54 Impact Factor