Lab Overview
Our laboratory is investigating the cell biology of the nuclear envelope.
Projects concern: a) mechanisms of nucleocytoplasmic transport, with focus
on the translocation of nuclear import receptors through the nuclear pore complex,
the import of adenovirus DNA during virus infection, and the molecular machinery
specifying HIV-1 mRNA export; b) functions of the nuclear lamina, particularly
the role of nuclear lamins and integral membrane proteins of the nuclear envelope
in nuclear functions and in human diseases.
Highlight
The nuclear lamina, a protein meshwork lining the inner nuclear membrane (INM),
contains a polymer of lamins together with associated transmembrane proteins.
The importance of the lamina to cell function is underscored by the finding
that over 15 inherited human diseases are caused by mutations in lamins and
associated proteins. Whereas it is widely accepted that the lamina is critical
for maintenance of NE structure, recent evidence suggests that the lamina also
functions in regulation of gene expression and signaling. Previously, in collaboration
with the Yates lab, we identified over 50 novel NE-enriched transmembrane proteins
(NETs) using a proteomics approach. Because many of the human diseases caused
by mutations in lamina components affect striated muscles, we have chosen to
analyze NET functions is C2C12 cells, a cultured myoblast model for muscle
differentiation. Using DNA microarray analysis we have identified a focus group
of NETs that are transcriptionally up-regulated during C2C12 myogenesis, and
that are expressed at high levels in adult mouse skeletal muscle relative to
other tissues. We found that RNAi-mediated silencing of one of these genes,
NET25, strongly inhibits myogenesis. NET25 is a truncated paralog of MAN1 (34%
identical), a previously studied INM protein that has been linked to human
bone diseases. MAN1 has been shown to attenuate TGF-? and BMP signaling through
inhibition of R-Smad phosphorylation. We determined that gene silencing of
MAN1 in C2C12 cells also blocks myogenesis. The silencing of either NET25 or
MAN1 inhibits the expression of myogenin, a transcription factor critical to
myogenesis that is induced when C2C12 cells are shifted to differentiation
medium. However, other aspects of the “molecular signature” arising
from silencing of NET25 and MAN1, defined by the expression of lamina and myogenic
proteins, are distinctive. These results indicate that NET25 and MAN1 have
essential, non-overlapping functions in C2C12 myogenesis. Since NET25 lacks
the Smad-binding domain found in MAN1, we propose that NET25 modulates an additional
signaling pathway(s) that is not affected by MAN1.
2006 Publications
Chen IH, Huber M, Guan T, Bubeck A, Gerace L. 2006. Nuclear envelope transmembrane
proteins (NETs) that are up-regulated during myogenesis. BMC Cell Biol. 7:38.
Wodrich H, Cassany A, D'Angelo MA, Guan T, Nemerow G, Gerace L. 2006. Adenovirus
core protein pVII is translocated into the nucleus by multiple import receptor
pathways. J Virol. 80:9608-18.
