HGF and plasma cell myeloma: Another study (28) established that osteoblasts induced myeloma cells to release MMP-1, urokinase plasminogen activator (uPA), and hepatocyte growth factor (HGF); conversely, contact with myeloma cells caused osteoblasts to produce MMP-1 in high amounts and the stimulation of osteoblastic MMP-1 expression by myeloma cells was driven by p38.