Cell surface expression of paraneoplastic encephalomyelitis/sensory neuronopathy-associated Hu antigens in small-cell lung cancers and neuroblastomas

Background: Serum from patients with small-cell lung cancer-associated paraneoplastic encephalomyelitis/sensory neuronopathy contains autoantibodies recognizing 35- to 40-kDa nuclear antigens present in neurons, small-cell lung cancers, and some neuroblastomas (anti-Hu). Aim: Because the mechanisms by which Hu autoantibodies may contribute to the paraneoplastic syndrome are largely unknown, we sought to examine if Hu antigens are expressed at the plasma membrane of cultured cells from Hu-expressing tumors. Methods and results: Hu-related molecules of 35 to 41 kDa were detected in the membrane of small-cell lung cancers and neuroblastomas using: (1) immunofluorescence, (2) absorption assays, (3) Western blotting on membrane fractions, and (4) surface biotinylation. The antibodies recognizing these membrane components were specifically absorbed by recombinant HuD protein. There was a perfect correlation between nuclear and membrane Hu expression. To determine the purity of the subcellular fractions, their reactivity with antibodies recognizing the A2 nuclear ribonucleoprotein and the cytoplasmic mitogen-activated protein kinase was examined. None of them was detected in the membrane fractions reactive with sera containing Hu antibodies. Conclusions: Hu-related antigens can be detected both in the nucleus and the membrane of small-cell lung cancer and neuroblastomas. Implications: These results provide an experimental basis for surface binding-mediated pathogenic mechanisms in paraneoplastic encephalomyelitis/sensory neuronopathy and in Hu-expressing tumors.