Our lab has identified a protein called NOM1 that is highly conserved from yeast to
humans and that we have shown is required for ribosome biogenesis. We have also
demonstrated that decreased levels of NOM1 result in cells that are smaller than
normal and that fail to proliferate. We hypthosize that NOM1 depletion activates a
p38 MAPK-dependent pathway that establishes both a G1 and a G2/M cell cycle
arrest. I am investigating the functions of NOM1 required for normal cell growth and
proliferation and am focusing on (1) NOM1’s ability to localize to and to target
proteins to the nucleolus, the sight of ribosome biogenesis, and (2) NOM1’s ability to
bind Protein Phosphatase I (PP1), a protein required for cell signaling, cell division,
and metabolism. This experiment is accomplished by first decreasing levels of
endogenous NOM1 in the cell using lentiviral vectors that encode short hairpin RNAs
that bind NOM1 mRNA and target it for degradation. Next, these cells are either left
untreated or transfected with one of three different NOM1 expression constructs. One
encodes the full length NOM1 protein that should rescue growth and proliferation of
the NOM1 depleted cells. The other two constructs contain either a deletion of the
nucleolar targeting domain of NOM1 or a mutation within the NOM1 PPI binding site.
The ability of these mutant constructs to rescue NOM1 depleted cells will reveal
whether either nucleolar targeting and/or PP1 binding is essential for NOM1 function.
These studies are important to define pathways and downstream events that respond
to deficiencies in ribosome production, a process disrupted in several human
diseases including several bone marrow failure syndromes.