Additional members of the rat liver lamin polypeptide family. Structural and immunological characterization

In addition to lamins A, B, and C (Gerace, L., Blum, A., and Blobel, G. (1978) J. Cell Biol. 79, 546-566), the rat liver nuclear lamina has recently been shown to contain two higher molecular weight (70,000-75,000, pI 5.7-5.8) quantitatively less prominent nuclear polypeptides (Lehner, C.F., Kurer, V., Eppenberger, H. M., and Nigg, E. A. (1986) J. Biol. Chem. 261, 13293-13301). In the present study two-dimensional tryptic peptide mapping and Western blotting with affinity-purified chicken and human sera have been utilized to examine the structural relationships and the tissue distribution of these quantitatively less prominent mammalian lamins (termed lamins D and E in this study). Lamins D and E have indistinguishable one- and two-dimensional proteolytic maps. Whereas the one-dimensional proteolytic maps of lamins D and E show several degradation products which are of similar molecular mass to polypeptides seen in one-dimensional proteolytic maps of lamins A, B, and C, the two-dimensional tryptic maps of D and E are distinct from those of lamins A, B, and C, suggesting that lamins D and E are produced by transcription of one or more unique genes. Nonetheless, affinity-purified anti-D/E antibodies (raised against lamin E) cross-react with lamin B, suggesting the presence of a shared epitope. Moreover, a human autoantibody cross-reacts with all five lamins after affinity elution from any of the five, suggesting the presence of another epitope which is shared by all five polypeptides. All five lamins were undetectable in rodent epididymal sperm. In contrast, lamins D and E were readily detected in a variety of rat somatic tissues (liver, kidney, prostate, brain, heart) including lymphoid cells, a cell type depleted of lamins A and C. During mitogenic stimulation of lymphocytes, the signal for lamins A and C increased 5-fold, the signal for lamins D and E increased 2-fold, but the signal for lamin B remained unchanged, suggesting that levels of lamins D and E are regulated independently from those of the major lamins.