Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:3.6.3.44 (P-glycoprotein)
 13,344 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

In the present study we have analyzed the involvement of phosphorylation in the function of P-glycoprotein and have also examined sites of phosphorylation along the P-glycoprotein polypeptide chain. The results show that in HL60 cells isolated for resistance to vincristine the protein kinase inhibitor staurosporine induces a major inhibition in the phosphorylation of P-glycoprotein. Further studies show that under the same conditions in which staurosporine inhibits P-glycoprotein phosphorylation there is a concomitant increase in cellular drug accumulation and a major inhibition in drug efflux. Additional studies using pulse-chase experiments show that the P-glycoprotein phosphate groups are metabolically active and that the protein undergoes rapid cycles of phosphorylation and dephosphorylation in the cell. Structural analyses demonstrate that cleavage of 32P-labeled P-glycoprotein at Asp-Pro linkages with formic acid results in the formation of a major phosphorylated peptide of 35 kDa and a minor peptide of 42 kDa. Western blot analysis using site-specific anti-sera against P-glycoprotein suggests that P35 represents a phosphorylated fragment containing P-glycoprotein amino acids 446-744. Analysis of tryptic peptides using site-specific antisera identifies a second major phosphorylated region of P-glycoprotein which contains amino acids 745-1088. These studies thus suggest that phosphorylation plays an important role in the biological activity of P-glycoprotein. The results also indicate that two adjacent internal regions are highly phosphorylated in the P-glycoprotein molecule.
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PMID:Analysis of P-glycoprotein phosphorylation in HL60 cells isolated for resistance to vincristine. 167 14

Human liver carcinoma cells (BEL-7404) and human KB adenocarcinoma cells were selected by stepwise increases in cisplatin. Drug sensitivity assays indicated that the IC50 value for 7404-CP7.5 cells was 49 micrograms ml-1 cisplatin, 111-fold higher than for the parental hepatoma cells. The IC50 value for KB-CP10 cells was 38 micrograms ml-1 cisplatin, which is 1152-fold higher than for the parental KB cells. The 7404-CP7.5 cells were cross-resistant to methotrexate (39 x), 5-fluorouracil (23 x) and 6-mercaptopurine (13 x), but were sensitive to drugs which are known substrates for the multidrug transporter (P-glycoprotein), including colchicine, vinblastine and actinomycin D. Similar cross-resistance patterns were observed for KB-CP10 cells. No evidence of DNA amplification or expression of the MDR1 gene was found. One-dimensional sodium dodecyl sulphate-polyacrylamide gel electrophoresis showed increases in 52 kDa protein(s) in both the soluble cytosolic and crude membrane fractions in 7404-CP(r) cells and in KB-CP(r) cells. The amount of 52 kDa protein was proportional to the degree of resistance of the 7404-CP(r) cells to cisplatin. Two-dimensional gel analysis demonstrated that two polypeptides of molecular mass 52 and 50 kDa were overexpressed in the membrane fractions in both 7404-CP20 and KB-CP20 cells. Using amino acid microsequencing and Western blotting, major 52 kDa protein was identified as the mitochondrial heat shock protein hsp60. Two-dimensional gels of [35S]methionine-labelled polypeptides showed many other changes, including reduction in soluble proteins of approximately 57 kDa molecular weight in KB-CP20 cells, and of 35 kDa in both 7404-CP20 and KB-CP20 cells. These results suggest that alterations of certain proteins occur commonly in cisplatin-resistant cells, particularly proteins of molecular weight 52 and 50 kDa.
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PMID:Characterisation of high-level cisplatin-resistant cell lines established from a human hepatoma cell line and human KB adenocarcinoma cells: cross-resistance and protein changes. 771 Sep 28

Galectin-3 (Gal-3, LGALS3) is a pleotropic versatile, 29-35 kDa chimeric gene product, and involved in diverse physiological and pathological processes, including cell growth, homeostasis, apoptosis, pre-mRNA splicing, cell-cell and cell-matrix adhesion, cellular polarity, motility, adhesion, activation, differentiation, transformation, signaling, regulation of innate/adaptive immunity, and angiogenesis. In multiple diseases, it was found that the level of circulating Gal-3 is markedly elevated, suggesting that Gal-3-dependent function is mediated by specific interaction with yet an unknown ubiquitous cell-surface protein. Recently, we showed that Gal-3 attenuated drug-induced apoptosis, which is one of the mechanisms underlying multidrug resistance (MDR). Here, we document that MDR could be mediated by Gal-3 interaction with the house-keeping gene product e.g., Na+/K+-ATPase, and P-glycoprotein (P-gp). Gal-3 interacts with Na+/K+-ATPase and induces the phosphorylation of P-gp. We also find that Gal-3 binds P-gp and enhances its ATPase activity. Furthermore Gal-3 antagonist suppresses this interaction and results in a decrease of the phosphorylation and the ATPase activity of P-gp, leading to an increased sensitivity to doxorubicin-mediated cell death. Taken together, these findings may explain the reported roles of Gal-3 in diverse diseases and suggest that a combined therapy of inhibitors of Na+/K+-ATPase and Gal-3, and a disease specific drug(s) might be superior to a single therapeutic modality.
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PMID:Extracellular galectin-3 programs multidrug resistance through Na+/K+-ATPase and P-glycoprotein signaling. 2615 64