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, Using immunofluorescence and immunoblotting studies it was noted that several 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 the altered level of A-type lamin expression. Secondly, an abnormal localization of lamin A was observed, Intensely fluorescing lamin A aggregates were observed in the nucleus, rather than the typical perinuclear staining pattern, Confocal scanning laser microscopy revealed that the lamin A aggregates were indeed present throughout the internal nucleus, When these cells were extracted with Triton X-100 the nucleoplasmic 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 nuclear periphery after extraction with the non-ionic detergent, Immunoblotting 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 GLC-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 lamins colocalized with the vimentin cytoskeleton in this cell line.