Higher CDC2 Protein Levels Increase Cell Proliferation in PAH
A protein known as cell division cycle protein 2 (CDC2) enhances the proliferation of pulmonary artery smooth muscle cells — those lining the walls of lung arteries — in people with pulmonary arterial hypertension (PAH), a study reported.
Additionally, the increased level of CDC2 in these cells was found to be dependent on FOXM1 and PLK1, two inducers of cell growth.
Overall, the findings suggest that targeting CDC2 could be therapeutically beneficial for the treatment of PAH, the investigators said.
The study, “CDC2 Is an Important Driver of Vascular Smooth Muscle Cell Proliferation via FOXM1 and PLK1 in Pulmonary Arterial Hypertension,” was published in the International Journal of Molecular Sciences.
Among the main features of PAH is the thickening of the inner lining of blood vessels. As the vessels become thicker, blood pressure rises in the lungs. The proliferation of pulmonary arterial smooth muscle cells (PASMC) is known to be a contributing factor in this process.
Studies have shown that the expression (production) of transcription factor, FOXM1, and the proto-oncogene polo-like kinase 1, PLK1, is increased in PASMCs. Inhibition of these proteins’ expression reduces PASMC proliferation. A transcription factor is a protein that regulates gene activity.
FOXM1 and PLK1 are involved in cell cycle regulation and both of these proteins are associated with CDC2. This protein regulates the cell cycle leading through mitosis, a biological process in which a single cell divides into two identical daughter cells.
Exactly how increased FOXM1 and PLK1 expression lead to cell proliferation is still unknown.
To address this knowledge gap, scientists at Tufts Medical Center, Boston, Massachusetts, studied the expression of these proteins in PASMCs from people with hereditary PAH (HPAH) and idiopathic (no known cause) PAH, or IPAH.
Cells were isolated from the lungs of five PAH patients and five donors without PAH and grown in the lab. Protein from these cells was isolated and analyzed. CDC2 levels were found to be higher in PASMCs from PAH patients than cells from control donors.
Administration of FOXM1 and PLK1 blockers reduced the expression of CDC2 and these results were further validated when the team knocked down the gene activity of FOXM1 and PLK1. Knocking down FOXM1 or PLK1 lowered the expression of CDC2 by more than 50%.
However, knocking down CDC2 expression, or using pharmacological inhibition, had no effect on FOXM1 or PLK1. “This demonstrates that CDC2 expression is downstream of both FOXM1 and PLK1,” the scientists wrote.
No major changes were observed in the expression of CDC2-related proteins in cells from PAH patients.
Next, the researchers examined how inhibiting major enzyme regulators of CDC2 affected its expression. These enzymes control CDC2 activity by phosphorylating or dephosphorolating CDC2. Phosphorylation is the process by which a phosphate group is attached to a molecule by an enzyme, while dephosphorylation is the removal of phosphate group.
Results showed that blocking these enzymes via a pharmacological inhibitor or genetic approach decreased CDC2 protein expression.
CDC2 production then was assessed in pulmonary arteries obtained from a pulmonary hypertension (PH) rat model. PH-like disease was induced by injecting Sugen 5416, a blocker of the vascular endothelial growth factor receptor, and exposure to low oxygen.
Compared with control mice, the pulmonary arteries from the PH rat model group had increased RNA (produced from DNA) and protein expression of CDC2. “This shows that CDC2 is upregulated upon induction of PH in rats’ pulmonary arteries,” the investigators added.
Taken together, the findings suggest that increased expression of FOXM1 and PLK1 in PAH lead to increased expression of CDC2. This results in the abnormal proliferation of these cells in people with PAH.
According to the team, blocking CDC2 could reduce smooth muscle proliferation. However, the current CDC2 inhibitors are not considered specific or safe for use in conditions other than cancer.
“In this communication, we show that CDC2 expression is sharply increased in pulmonary artery smooth muscle cells from patients with PAH in comparison to normal PASMC cells. The expression of CDC2 is coordinated with increased expression of FOXM1 and PLK1 so that strong growth of the cells within the pulmonary artery is assured,” the researchers concluded.