Thesis (Ph. D.)--University of Washington, 2003. / Vita. Includes bibliographical references (leaves 101-113).

Masters of Science / Retinoblastoma Binding Protein 6 (RBBP6) is a RING finger-containing protein which plays a critical role in the 3'-end processing of mRNA transcripts. It is a constituent of the human pre-mRNA processing complex but also interacts directly with core splicing-associated proteins. RBBP6 also interacts with both major tumour suppressor proteins p53 and pRb and is known to play a critical role in suppression of p53 during development, in cooperation with MDM2. Through its RING finger it interacts with the C-terminus of the oncogenic protein Y-Box Binding Protein 1 (YB-1) both in vitro and in vivo, catalysing its ubiquitination and degradation in the proteasome. YB-1 is closely associated with tumour progression, poor patient prognosis and chemotherapeutic resistance, making it a promising target for therapeutic intervention. Unpublished data from our laboratory suggests that RBBP6 is able to poly-ubiquitinate YB-1 in vitro, using UbcH1 as the ubiquitin- conjugating enzyme (E2). This study aims to identify RBBP6 RING protein-protein interactions involved in the down regulation of YB-1 by RBBP6. These interactions include the C-terminal fragment of YB-1 (substrate), MDM2 (E3) and UbcH1 (E2). The C-terminal fragment of YB-1, denoted YB-1₂₂₀₋₃₂₄, was successfully cloned and expressed in bacteria and demonstrated to interact directly with the RBBP6 RING finger domain in in vitro affinity pull down assays. This is in good agreement with our unpublished data that RBBP6 is able to ubiquitinate full length YB-1 as well as the YB-1₂₂₀₋₃₂₄ fragment. UbcH1 was successfully expressed and shown to interact directly with RBBP6 RING in in vitro affinity pull down assays. This is also in agreement with our data showing that RBBP6 is able to ubiquitinate YB-1 using UbcH1 as E2. ¹⁵N-labelled samples of RBBP6 RING was successfully expressed in bacteria and used to investigate the putative interaction with UbcH1 in NMR-based chemical shift perturbation assays. However no interaction was observed, possibly because the sample of UbcH1 was subsequently found using mass spectrometery to be partially degraded. GST-tagged RBBP6 RING was able to precipitate MDM2 from HeLa lysate. This extends previous reports that full length RBBP6 and MDM2 interact directly and play a role in the suppression of p53 during development. The result was validated by showing that GST-MDM2 was able to precipitate RBBP6 RING in in vitro. This study includes a side project which involved the cloning and expression of DWNN-GG. GST-HADWNN-GG was successfully cloned and expressed in bacteria. An HA tag was included immediately upstream of DWNN-GG for immunodetection using anti-HA antibodies; the construct was designed in such as way that it could be re-used to generate HA-tagged versions of existing constructs cloned into pGEX-6P-2. The above findings lay the foundation for future structural and functional studies of the involvement of RBBP6 in regulation of the cancer-related proteins p53 and YB-1, which may have far-reaching consequences in the fight against cancer. / National Research Foundation (NRF)

Diss. (sammanfattning) Stockholm : Karol. inst., 2004. / Härtill 5 uppsatser.

Thesis (Ph. D.)--School of Pharmacy. University of Missouri--Kansas City, 2007. / "A dissertation in pharmaceutical science and pharmacology." Advisor: Ashim K. Mitra. Typescript. Vita. Title from "catalog record" of the print edition Description based on contents viewed July 16, 2008. Includes bibliographical references (leaves 231-248). Online version of the print edition.

Indiana University-Purdue University Indianapolis (IUPUI) / Human BCRP is one of the major ATP-binding cassette transporters involved in the development of multidrug resistance in cancer chemotherapy. Overexpression of BCRP in the tumor cell plasma membrane and apical membrane of the gastrointestinal tract leads to decreased intracellular accumulation of various anticancer drugs as well as reduced drug bioavailability. BCRP has been shown to exist on the plasma membrane as higher forms of homo-oligomers. In addition, the oligomerization domain of BCRP has been mapped to the carboxyl-terminal TM5-ECL3-TM6 and this truncated domain, when co-expressed with the full-length BCRP, displays a dominant inhibitory activity on BCRP function. Thus, the oligomerization of BCRP could be a promising target in reversing multidrug resistance mediated by BCRP. To further dissect the oligomerization domains of human BCRP and test the hypothesis that TM5, ECL3, and TM6 each plays a role in BCRP oligomerization and function, we engineered a series of BCRP domain-swapping constructs with alterations at TM5-ECL3-TM6 and further generated HEK293 cells stably expressing wild-type or each domain-swapping construct of BCRP. Using co-immunoprecipitation and chemical cross-linking, we found that TM5, ECL3, and TM6 all appear to partially contribute to BCRP oligomerization, which are responsible for the formation of oligomeric BCRP. However, only TM5 appears to be a major contributor to the transport activity and drug resistance mediated by BCRP, while ECL3 or TM6 is insufficient for BCRP functions. Taken together, these findings suggest that homo-oligomeric human BCRP may be formed by the interactions among TM5, ECL3 and TM6, and TM5 is a crucial domain for BCRP functions and BCRP-mediated drug resistance. These findings may further be used to explore targets for therapeutic development to reverse BCRP-mediated drug resistance and increase the bioavailability of anti-cancer drugs for better treatment of multidrug resistant cancers.

Thesis (Ph.D.). / Written for the Institute of Parasitology. Title from title page of PDF (viewed 2008/02/12). Includes bibliographical references.

Diss. (sammanfattning) Linköping : Linköpings universitet, 2005. / Härtill 4 uppsatser. På omsl. felaktigt " ... daunorobicin ..."

Exposure to toxic bile acids (BA) and retinoic acids (RA) is implicated in toxicities related to excessive oxidative stress. This thesis examined roles and mechanisms of the oxidative stress-responsive nuclear factor (erythroid 2-like) factor 2 (Nrf2) in adaptive cell defense against BA and RA toxicities. Using liver cells and mouse models, many antioxidant proteins known to be Nrf2 target genes, particularly the rate-limiting enzyme for glutathione (GSH) biosynthesis, i.e., glutamate-cysteine ligase subunits (GCLM/GCLC), were induced by BA [lithocholic acid (LCA)] or RA (all-trans, 9-cis and 13-cis) treatment. Evidence for increased Nrf2 transactivation by LCA and all-trans-RA was exemplified in HepG2 by: (1) reduced constitutive and inducible expression of GCLM/GCLC upon Nrf2 silencing via small-interfering RNA; (2) increased inducible expression of GCLM/GCLC genes by Nrf2 overexpression, but overexpression of dominant-negative Nrf2 decreased it; (3) increased nuclear accumulation of Nrf2 as signature event of receptor activation; (4) enhanced Nrf2-dependent antioxidant-response-element (ARE) reporter activity as indicative of increased Nrf2 transactivation; and (5) increased Nrf2 occupancy to AREs of GCLM and GCLC. Additionally, in BA-treated HepG2 cells, we observed concomitant increases of many ATP-binding cassette (ABC) transporters (MRPs 1-5, MDR1 and BCRP) in parallel with increased cellular efflux. Nrf2 silencing in HepG2 cells decreased constitutive and inducible expression of MRP2, MRP3 and ABCG2. However, Nrf2-silenced mouse hepatoma cells, Hepa1c1c7, and Nrf2-/- mice had decreased constitutive and/or inducible expression of Mrps 1-4, suggesting species differences in Nrf2-dependent regulation of hepatic ABC transporters. Protection by Nrf2 against BA and RA toxicities was confirmed by observations that Nrf2 silencing increased cell susceptibility to BA- and RA-induced cell death. Moreover, Nrf2-/- mice suffered more severe liver injury than the wildtype. Increased GSH and efflux activity following increased GCLM/GCLC and ABC transporters, respectively, can mitigate LCA toxicity. Activation of MEK1-ERK1/2 MAPK was shown to primarily mediate Nrf2 transactivation and LCA-induced expression of antioxidant proteins and Nrf2-dependent and -independent ABC transporters. In conclusion, Nrf2 activation by BA and RA led to coordinated induction of antioxidant and ABC proteins, thereby counteracting resultant oxidative cytotoxicity. The potential of targeting Nrf2 in management of BA and RA toxicities merits further investigation.

Exposure to toxic bile acids (BA) and retinoic acids (RA) is implicated in toxicities related to excessive oxidative stress. This thesis examined roles and mechanisms of the oxidative stress-responsive nuclear factor (erythroid 2-like) factor 2 (Nrf2) in adaptive cell defense against BA and RA toxicities. Using liver cells and mouse models, many antioxidant proteins known to be Nrf2 target genes, particularly the rate-limiting enzyme for glutathione (GSH) biosynthesis, i.e., glutamate-cysteine ligase subunits (GCLM/GCLC), were induced by BA [lithocholic acid (LCA)] or RA (all-trans, 9-cis and 13-cis) treatment. Evidence for increased Nrf2 transactivation by LCA and all-trans-RA was exemplified in HepG2 by: (1) reduced constitutive and inducible expression of GCLM/GCLC upon Nrf2 silencing via small-interfering RNA; (2) increased inducible expression of GCLM/GCLC genes by Nrf2 overexpression, but overexpression of dominant-negative Nrf2 decreased it; (3) increased nuclear accumulation of Nrf2 as signature event of receptor activation; (4) enhanced Nrf2-dependent antioxidant-response-element (ARE) reporter activity as indicative of increased Nrf2 transactivation; and (5) increased Nrf2 occupancy to AREs of GCLM and GCLC. Additionally, in BA-treated HepG2 cells, we observed concomitant increases of many ATP-binding cassette (ABC) transporters (MRPs 1-5, MDR1 and BCRP) in parallel with increased cellular efflux. Nrf2 silencing in HepG2 cells decreased constitutive and inducible expression of MRP2, MRP3 and ABCG2. However, Nrf2-silenced mouse hepatoma cells, Hepa1c1c7, and Nrf2-/- mice had decreased constitutive and/or inducible expression of Mrps 1-4, suggesting species differences in Nrf2-dependent regulation of hepatic ABC transporters. Protection by Nrf2 against BA and RA toxicities was confirmed by observations that Nrf2 silencing increased cell susceptibility to BA- and RA-induced cell death. Moreover, Nrf2-/- mice suffered more severe liver injury than the wildtype. Increased GSH and efflux activity following increased GCLM/GCLC and ABC transporters, respectively, can mitigate LCA toxicity. Activation of MEK1-ERK1/2 MAPK was shown to primarily mediate Nrf2 transactivation and LCA-induced expression of antioxidant proteins and Nrf2-dependent and -independent ABC transporters. In conclusion, Nrf2 activation by BA and RA led to coordinated induction of antioxidant and ABC proteins, thereby counteracting resultant oxidative cytotoxicity. The potential of targeting Nrf2 in management of BA and RA toxicities merits further investigation.