```python
import pyqtgraph as pg
from pyqtgraph import GraphItem
from pyqtgraph.Qt import QtGui

class CustomGraphItem(GraphItem):
    def __init__(self):
        super().__init__()
        self.setData()
    
    def setData(self):
        # Set data for nodes and lines
        pass
    
    def updateGraph(self):
        # Update the graph
        pass
    
    def mouseDragEvent(self, ev):
        # Handle mouse drag events
        pass
    
    def mouseClickEvent(self, ev):
        # Respond to clicks on the graph
        print("Node clicked")
    
# Create a GraphicsLayoutWidget
app = QtGui.QApplication([])
win = pg.GraphicsLayoutWidget()
win.setWindowTitle('pyqtgraph example: CustomGraphItem')

# Create an instance of CustomGraphItem
graph = CustomGraphItem()

# Add the graph to the GraphicsLayoutWidget
win.addItem(graph)

# Display the graph
win.show()

# Start the Qt event loop
app.exec_()
```