Nuclear pore complex oxalate binding protein p62: expression in different kidney disorders.
BACKGROUND
Urolithiasis is a multifactorial process that starts with the formation of microcrystals in the urine and terminates as mature renal calculi. The oxalate binding protein plays a vital role in the transport of oxalate. The physiological significance of the presence of oxalate binding protein in the nuclear pore complex is not well understood.


METHODS
The nuclear envelope was extracted from human cadaver kidneys. 14C oxalate was labeled, nuclear pore complex proteins were extracted and loaded onto Sephadex G-200, and further purified in DEAE-Sephadex A-50 column. The radioactive protein peak was pooled, concentrated and checked for purity in SDS-PAGE. The purified protein showed cross-reactivity with the monoclonal antibody (MAb 414) and was homogeneous. Urine samples of healthy individuals with no history of kidney disease served as control. Blood and urine samples were collected from kidney and autoimmune disorder patients and checked for the expression of p62 protein by ELISA.


RESULTS
Extracted and purified nuclear pore complex oxalate binding protein had a molecular weight of 62 kDa. A threefold increase in oxalate excretion was observed in hyperoxaluric patients compared to control subjects. The protein expression was found to be higher in hyperoxaluric patients vs. controls, chronic renal failure (CRF) and acute renal failure (ARF), whereas decreased expression was observed in nephrotic syndrome (NS) patients. p62 autoantibodies was observed in hyperoxaluria (HO), systemic lupus erythematosus (SLE) and primary biliary cirrhosis (PBC), whereas it was absent in controls.


CONCLUSIONS
Increased expression of p62 may be due to membrane damage induced by oxalate stress, and may be used as a diagnostic marker. This study also confirms the presence of p62 autoantibodies in HO patients.
Department of Medical Biochemistry, University of Madras, Taramani, Chennai-113, India.
P
P
Sivakamasundari
P
P
Kalaiselvi
R
R
Sakthivel
R
R
Selvam
P
P
Varalakshmi
D001323:Autoantibodies / Q000032:analysis; D015153:Blotting, Western; D002852:Chromatography, Ion Exchange; D004591:Electrophoresis, Polyacrylamide Gel; D004797:Enzyme-Linked Immunosorbent Assay; D006801:Humans; D006959:Hyperoxaluria / Q000378:metabolism; D066298:In Vitro Techniques; D007668:Kidney / Q000378:metabolism; D007669:Kidney Calculi / Q000378:metabolism; D007674:Kidney Diseases / Q000378:metabolism*; D008562:Membrane Glycoproteins / Q000096:biosynthesis* / Q000302:isolation & purification / Q000652:urine; D008970:Molecular Weight; D022022:Nuclear Pore / Q000737:chemistry; D028861:Nuclear Pore Complex Proteins
D001323:Autoantibodies; D008562:Membrane Glycoproteins; D028861:Nuclear Pore Complex Proteins; C049312:nuclear pore protein p62