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Our laboratory is investigating the role of cell cycle proteins,
specifically the cyclin-dependent kinase inhibitors (CKIs), in regulating
vascular development and vascular repair. We have pursued several
lines of investigation. Previously, we observed that inhibition
of vascular smooth muscle cell proliferation in injured vascular
tissues is regulated by the CKI p27. To determine how modifications
in p27 alter proliferation responses, we cloned and characterized
a kinase, kinase interacting strathum or KIS. This kinase phosphorylates
p27 at serine 10 leading to nuclear export of p27, phosphorylation
on threonine 187, and proteolytic degradation by ubiquitination.
It is activated by mitogens during G0/G1 phase of the cell cycle,
and its expression overcomes growth arrest induced by p27, leading
to cell cycle progression. Because KIS may be an important differentiation
factor in other cell systems, we are investigating the structure
and function of this protein further. We have sequenced and characterized
the KIS promoter, confirming mitogen activation of the kinase. KIS
is expressed in the developing heart, vasculature, and brain where
it functions to regulate cell proliferation and differentiation.
In the developing heart, KIS appears to be regulated by transcription
factors that are critical for cardiac development.
We are also examining the expression and function of p27 in arterial
wound repair and remodeling. In these studies, we are using genetically
engineered mice. Mice lacking p27 have accelerated lesion formation
following vascular stresses due to uncheck proliferation of vascular
smooth muscle cells, T-cell inflammatory responses, and altered
collagen formation. Crosses of CKI p27 mice with other CKI knock-outs,
including p21 and rag null mice, have enabled us to study the mechanisms
of inflammation and proliferation. Interestingly, a deficiency of
p27 in an apoE null background severely accelerates atherosclerosis.
Two other cell cycle proteins have been studied: protein arginine
methyltransferase 2 (PRMT2) that regulates phosphorylation of the
retinoblastoma gene product, Rb, and minichromosome maintaining
protein 7 (MCM7) that is critical for initiation of DNA replication.
To understand the relevance of cell cycle signaling pathways in
human vascular disease, we have initiated a clinical study of patients
with coronary artery disease who are undergoing stent placement.
Patients who experience clinical restenosis will be compared to
those patients whose percutaneous procedures are successful. Gene
expression profiling and proteomic approaches are being used to
investigate differences between the two groups. Gene and protein
expression patterns are analyzed to determine the genotype of the
patients. Molecular profiling will be helpful in predicting the
outcome of percutaneous coronary interventions for coronary artery
disease. Taken together, these studies define molecular and cellular
signaling pathways important in the pathogenesis of vascular diseases.
Understanding these pathways is critical to the design and development
of new therapies for cardiovascular diseases.
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