Honokiol inhibits migration of renal cell carcinoma through activation of RhoA/ROCK/MLC signaling pathway

Honokiol, a biologically active compound isolated from Magnolia bark, has been shown to possess promising anticancer effect through induction of apoptosis. However, there is a relative lack of information regarding its anti-metastatic activity. Renal cell carcinoma (RCC) is the most common malignancy of the adult kidney and is known for high risk of metastasis. Clinically, therapeutic methods for metastatic RCC cases are limited and efforts to exploit new treatments are still ongoing. The results of our current investigation first revealed that honokiol suppressed the proliferation of different human RCCs without affecting cell viability. In addition, honokiol inhibited migration of highly metastatic RCC 786-0 cells and stimulated the activity of small GTPase, RhoA. Furthermore, phosphorylated myosin light chain (MLC) and excessive formation of actin stress fibers were identified in 786-0 cells treated with honokiol. Interestingly, the pharmacological Rho-associated protein kinase (ROCK) inhibitor Y-27632 attenuated contraction of actin stress fibers induced by honokiol and abrogated honokiol-mediated inhibition of cell migration. Together these important findings suggest that honokiol suppresses the migration of highly metastatic RCC through activation of RhoA/ROCK/MLC signaling and warrants attention in the treatment of RCC metastasis as a novel therapeutic approach.