Multidrug resistance P-glycoprotein monoclonal antibody JSB-1 crossreacts with pyruvate carboxylase.
Multidrug resistance ( MDR) is associated with overexpression of a 170 KD plasma membrane P-glycoprotein ( P-gp), a putative energy-dependent efflux transporter that reduces intracellular accumulation of chemotherapeutic agents. For detection of P-gp expression in normal and malignant tissues, an MDR1-specific monoclonal antibody (MAb) JSB-1 has been used extensively. In this report we show that MAb JSB-1 crossreacts with a protein of M(r) approximately 130,000 present in rat liver mitochondrial inner membrane/matrix fractions. Peptide mapping and microsequencing identify this protein as pyruvate carboxylase ( PC), an abundant mitochondrial enzyme. MAb JSB-1 also crossreacts with purified PC from bovine liver. Under immunoblotting conditions, this crossreactivity is partially abolished by pre-incubation of MAb JSB-1 with a 1000-fold molar excess of MAb C494 epitope-specific peptide (PNTLEGN), indicating that the epitope of MAb JSB-1 may either overlap with or be in close proximity to that of MAb C494. Immunohistochemical cross-reactivity was also demonstrated in cryosections of human skeletal muscle, a tissue known not to express P-gp. MAb JSB-1 strongly immunostained Type 1 fibers, the subtype known to contain abundant mitochondria. Use of MAb JSB-1 for detection of MDR1 P-gp expression should be approached with caution.[1]References
- Multidrug resistance P-glycoprotein monoclonal antibody JSB-1 crossreacts with pyruvate carboxylase. Rao, V.V., Anthony, D.C., Piwnica-Worms, D. J. Histochem. Cytochem. (1995) [Pubmed]
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