ABNORMAL A-TYPE LAMIN ORGANIZATION IN A HUMAN LUNG-CARCINOMA CELL-LINE

We have studied the expression of lamins A and C (A-type lamins) in a lung carcinoma cell line using type-specific monoclonal antibodies, Us ing immunofluorescence and immunoblotting studies it was noted that se veral irregularities in lamin expression exist in the cell line GLC-A1 , derived from an adenocarcinoma, First, the expression of the A-type lamins was lower than in other adenocarcinoma cell lines of the lung. Also the ratio between lamins A and C proteins was 1:8 instead of the 1:1 ratio seen in the other cell lines, Northern blotting con firmed t he altered level of A-type lamin expression. Secondly, an abnormal loc alization of lamin A was observed, Intensely fluorescing lamin A aggre gates were observed in the nucleus, rather than the typical perinuclea r staining pattern, Confocal scanning laser microscopy revealed that t he lamin A aggregates were indeed present throughout the internal nucl eus, When these cells were extracted with Triton X-100 the nucleoplasm ic aggregates disappeared, which indicates that the A-type lamins are not properly incorporated into the lamina. The A-type lamins in other cell lines derived from adenocarcinomas remained present in the nuclea r periphery after extraction with the non-ionic detergent, Immunoblott ing studies of the Triton X-100 soluble and insoluble fractions showed that lamin A and an apparently truncated product, which was detected with the lamin A antibody, were present in the insoluble fraction of G LC-A1. This truncated product is partly Triton X-100 soluble since it was also detected in the detergent soluble fraction, Thirdly, using an antibody to A-type lamins sporadic GLC-A1 cells showed a filamentous cytoplasmic staining pattern, which was Triton X-100 resistant, Double labeling immunofluorescence studies revealed that these cytoplasmic l amins colocalized with the vimentin cytoskeleton in this cell line.