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Departments of Cell and Molecular Biology, The Scripps Research Institute, La Jolla, California 92037
Lamina-associated polypeptide 2 (LAP2) is
an integral membrane protein of the inner nuclear
membrane that binds to both lamin B and chromatin
and has a putative role in nuclear envelope (NE) organization. We found that microinjection of a recombinant polypeptide comprising the nucleoplasmic domain
of rat LAP2 (residues 1-398) into metaphase HeLa
cells does not affect the reassembly of transport-competent nuclei containing NEs and lamina, but strongly
inhibits nuclear volume increase. This effect appears to
be specifically due to lamin binding, because it also is
caused by microinjection of the minimal lamin-binding
region of LAP2 (residues 298-373) but not by the chromatin-binding domain (residues 1-88). Injection of the
lamin-binding region of rat LAP2 into early G1 phase
HeLa cells also strongly affects nuclear growth; it almost completely prevents the threefold nuclear volume
increase that normally occurs during the ensuing 10 h.
Moreover, injection of the fragment during early G1
phase strongly inhibits entry of cells into S phase, whereas injection during S phase has no apparent effect
on ongoing DNA replication. Since the lamin-binding
fragment of LAP2 most likely acts by inhibiting dynamics of the nuclear lamina, our results suggest that a normal function of LAP2 involves regulation of nuclear
lamina growth. These data also suggest that lamina dynamics are required for growth of the NE and for nuclear volume increase during the cell cycle, and that
progression into S phase is dependent on the acquisition of a certain nuclear volume.
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