Disease relevance of RALBP1

• Our recent studies have suggested that RALBP1 present in MCF-7 breast cancer cells has significantly lower specific activity for transport of DOX than wild-type recombinant protein, and its level of expression is significantly lower than that in lung cancer cells [1].
• Present studies in K562 human myelogenous leukemia show that RALBP1 overexpression confers broad resistance to multiple chemotherapy drugs including cisplatin, melphalan, doxorubicin, daunorubicin, vincristine, vinblastine, vinorelbine, and mitomycin-C [2].
• RLIP76/RALBP1 is a multi-specific drug-transporter which can mediate drug-resistance in lung and other cancers, but its ability to mediate multidrug-resistance has not been previously demonstrated in hematological malignancy [2].
• RLIP76 expressed in E. coli was purified by DNP-SG affinity chromatography [3].
• The role of PKCalpha and RLIP76 in transport-mediated doxorubicin-resistance in lung cancer [4].
• Augmentation of cellular levels of Hsf-1 and POB1 caused dramatic apoptosis in non-small cell lung cancer cell line H358 through Ralbp1 inhibition [5].

Psychiatry related information on RALBP1

• In this article, we discuss the significance of transport functions of RLIP76 highlighting its role in the defense mechanisms against oxidative injury, and modulation of signaling mechanisms [6].

High impact information on RALBP1

• Activation of IKK by TNFalpha requires site-specific ubiquitination of RIP1 and polyubiquitin binding by NEMO [7].
• A point mutation of RIP1 at Lys-377 (K377R) abolishes its polyubiquitination as well as its ability to restore IKK activation in a RIP1-deficient cell line [7].
• Doxorubicin-stimulated ATP hydrolysis by DNP-SG ATPase was saturable with respect to doxorubicin (Km 1.2 and 2.8 microM for the lung and erythrocyte enzymes, respectively) [8].
• We now demonstrate that DNP-SG ATPase purified from human lung and erythrocyte membranes catalyzed the hydrolysis of ATP in the presence of doxorubicin and its metabolites [8].
• Antibodies against DNP-SG ATPase immunoprecipitated the ATP hydrolyzing activity stimulated by doxorubicin, its metabolites, and glutathione conjugates [8].

Chemical compound and disease context of RALBP1

• Doxorubicin transport by RALBP1 and ABCG2 in lung and breast cancer [1].
• In some cells (e.g., erythrocytes and lung cancer cells), the majority of transport activity for Adriamycin and glutathione conjugates including LTC4 is accounted for by RLIP76 [9].
• RLIP76-/- knockout mice exhibited dramatic toxicity upon phenytoin administration due to decreased drug extrusion mechanisms at the blood-brain barrier [10].
• The Rex protein of human T-cell leukemia virus type 1, like the functionally equivalent Rev protein of human immunodeficiency virus type 1, contains a leucine-rich activation domain that specifically interacts with the human nucleoporin-like Rab/hRIP cofactor [11].
• RLIP76 or one of its derived deletion mutants was expressed in Escherichia coli, and bacteria were lysed and extracted in buffer without or with the nonionic detergent polidocanol [12].

Biological context of RALBP1

• POB1 over-expression inhibits RLIP76-mediated transport of glutathione-conjugates, drugs and promotes apoptosis [13].
• RLIP76 (RALBP1) is a glutathione-conjugate transporter that is a critical component of clathrin-coated pit-mediated endocytosis, as well as in stress responses [14].
• Transport of glutathione conjugates and chemotherapeutic drugs by RLIP76 (RALBP1): a novel link between G-protein and tyrosine kinase signaling and drug resistance [15].
• POB1 is a binding protein of RalBP1 and has the Eps15 homology (EH) domain [16].
• Competitive control of independent programs of tumor necrosis factor receptor-induced cell death by TRADD and RIP1 [17].

Anatomical context of RALBP1

• Results of these studies show lower protein expression and specific activity of RALBP1 in all three breast cancer cell lines as compared with lung cancer cell lines [1].
• Ral and POB1 simultaneously interacted with RalBP1 in COS cells [18].
• During mitosis, RLIP76 is located on the duplicated centrosomes and is required for their proper separation and movement to the poles [19].
• However, when RalBP1 was coexpressed with Ral(G23V/C203S), all of RalBP1 was recovered in the cytosol fraction [20].
• Immunohistochemical studies using a fluorescent probe showed association of RLIP76 with erythrocyte membrane, which was consistent with its transport function [21].

Associations of RALBP1 with chemical compounds

• RLIP76 (RALBP1) is a Ral-binding nucleotidase which functions as an energy-dependent transporter for glutathione (GSH)-conjugates as well as structurally unrelated xenobiotics [13].
• Both doxorubicin and a model GSH-conjugate, dinitrophenyl-S-glutathione (DNP-SG), transport were inhibited by POB1 in a concentration-dependent manner but not by POB1(1-512), lacking RLIP76-binding site [13].
• A key step in the mercapturic acid pathway, efflux of the glutathione-electrophile conjugate has recently been shown to be catalyzed largely by the stress-responsive protein RLIP76, a splice variant peptide endowed by the human gene RALBP1 [22].
• Depletion of Triad3A by small interference RNA treatment inhibited geldanamycin-activated ubiquitination and proteolytic degradation of RIP1 [23].
• These results suggest that RalBP1 makes a complex with POB1 and that this complex may provide a link between tyrosine kinase, Src homology 3 (SH3)-containing protein, and Ral [18].

Physical interactions of RALBP1

• Mu2, the medium chain of the AP2 complex is shown to interact with RLIP76 [24].
• Furthermore, we demonstrate that RALBP1 contributes only a minor fraction of DOX transport activity in breast cancer cell lines, suggesting that greater DOX sensitivity of breast cancer may be related to lower RALBP1 transporter activity and that the transport mechanisms involved in multidrug resistance of lung and breast cancer are distinct [1].

Enzymatic interactions of RALBP1

• PKC-alpha catalyzed phosphorylation of RLIP76 and increased its transport activity by 2-3-fold [25].
• A serine kinase associates with the RAL GTPase and phosphorylates RAL-interacting protein 1 [26].

Regulatory relationships of RALBP1

• These results reveal the biochemical mechanism underlying the essential signaling function of NEMO and provide direct evidence that signal-induced site-specific ubiquitination of RIP1 is required for IKK activation [7].
• These results suggest that RLIP76 is the major LTC(4) transporter in cancer cells and that its transport activity is regulated by PKC-alpha-mediated phosphorylation [25].
• Ral-binding protein 1 (RalBP1) is a putative effector protein of Ral and possesses the GTPase-activating activity for Rac1 and CDC42 [20].
• Stress-pre-conditioned cells with induced hGST5.8 and RLIP76 acquired resistance to 4-HNE and H2O2-mediated apoptosis by suppressing a sustained activation of c-Jun N-terminal kinase and caspase 3 [27].
• The antibodies raised against human erythrocyte Dnp-SG ATPase cross-reacted with the bovine lens epithelium Dnp-SG ATPase which was identified by Western blot as a band corresponding to an approximate M(r) value of 80,000 Da [28].

Other interactions of RALBP1

• However, internalization of transferrin was unaffected by Ral, RalBP1, POB1 and their mutants [16].
• Stimulation of tumor necrosis factor receptor 1 (TNFR1) can initiate several cellular responses, including apoptosis, which relies on caspases, necrotic cell death, which depends on receptor-interacting protein kinase 1 (RIP1), and NF-kappaB activation, which induces survival and inflammatory responses [17].
• RLIP76, an effector of the GTPase Ral, interacts with the AP2 complex: involvement of the Ral pathway in receptor endocytosis [24].
• We demonstrate RLIP76 reconstituted in artificial liposomes can catalyze ATP-dependent transport of LTC(4), which can be modulated by PKC-alpha [25].
• We examined the roles of the post-translational modifications of Ral and Rac1 for the action of RalBP1 [20].

Analytical, diagnostic and therapeutic context of RALBP1

• Multiple sequence alignment analysis suggested that RIP1 contains a TIR homologous domain, and mutation of amino acid residues in this domain identified three residues critical for its interaction with Triad3A [23].
• In Western blot analyses using antibodies against RLIP76, a strong expression of RLIP76 was observed in erythrocytes [21].
• Western blot analyses and immunohistochemistry studies showed no recognition of other protein in crude NSCLC cell homogenates by anti-RLIP76, confirming the specificity of anti-RLIP76 IgG [29].
• In immunohistochemistry and flow cytometry studies, these antibodies recognized RLIP76 domain(s) on the cell surface [29].
• RLIP76 was purified from each cell line and homogeneity demonstrated by SDS-PAGE and amino acid composition analysis [30].

References