Role of Rac1/WAVE2 Signaling in Mediating the Inhibitory Effects of γ-Tocotrienol on Mammary Cancer Cell Migration and Invasion

Abstract

The majority of breast cancer deaths result from the progression of this disease to a metastatic phenotype. Rac1 and Cdc42 are Rho family members that together with their downstream effectors, Wiskott-Aldrich Syndrome protein-family verprolin-homologous protein 2 (WAVE2) and Arp2/3, play an important role in cytoskeletal reorganization and the formation of membrane protrusions that promote cancer cell migration and invasion. γ-Tocotrienol, is a natural isoform within the vitamin E family of compounds that inhibits breast cancer cell growth and progression by suppressing various signaling pathways involved in mitogenic signaling and metastatic progression. Studies were conducted to examine the effects of γ-tocotrienol on Rac1/WAVE2 signaling dependent migration and invasion in highly metastatic mouse SA and human MDA-MB-231 mammary cancer cells. Exposure to γ-tocotrienol resulted in a dose-responsive decrease in Rac1/WAVE2 signaling as characterized by a suppression in the levels of Rac1/Cdc42, phospho-Rac1/Cdc42, WAVE2, Arp2, and Arp3 expression. Additional studies also demonstrated that similar treatment with γ-tocotrienol resulted in a significant reduction in tumor cell migration and invasion. Taken together, these findings indicate that γ-tocotrienol treatment effectively inhibits Rac1/WAVE2 signaling and reduces metastatic phenotypic expression in mammary cancer cells, suggesting that γ-tocotrienol may provide some benefit as a novel therapeutic approach in the treatment of metastatic breast cancer.Key words γ-tocotrienol; breast cancer; Rac1; Wiskott-Aldrich Syndrome protein-family verprolin-homologous protein 2 (WAVE2); migration; invasion Breast cancer is the most common form of cancer in women and is second only to lung cancer as a leading cause of cancer mortality in the United States.1,2) The vast majority of breast cancer deaths result from the development and progression of the metastatic form of this disease, that is characterized by cancer cells detaching from the primary tumor and spreading to distant sites in the body such as the bone, brain, surrounding lymph nodes, liver, and lungs.3-5) Breast cancer metastasis is a complex and multistep process that includes morphological changes, detachment from the basement membrane, increased mobility and invasion into surrounding tissues, intravasation, circulation, adhesion, extravasation, and growth at distant sites. 6) Since patient prognosis for metastatic breast cancer is very poor, there is great interest in developing antiinvasion therapies to improve patient treatment and survival. 7)An initial step in the metastasis process involves epithelialto-mesenchymal transition (EMT), where neoplastic epithelial cells lose their cellular polarity and acquire mesenchymal-like mobility that allows them to invade surrounding tissues. [8][9][10][11] This amoeboid-like movement requires the formation of cellular protrusions that result from the conversion of monomeric globular actin (G-actin) to polymerized filamentous actin (Factin). 12-15)The Rho family of sm...

Vitamin E and cancer prevention: Studies with different forms of tocopherols and tocotrienols

“…147 Other properties of cancer cells such as cell migration, cell invasion, and epithelial-mesenchymal transition have also been reported to be inhibited by tocotrienols in lung cancer cells, gastric cancer cells, and breast cancer cells in vitro, in cell migration assay, wound healing assay, and cell invasive assay. 119,123,153 In γ-T3-treated breast cancer MDA-MB-231 cells, cell migration machinery regulators such as RAC1 and WAVE2 signaling were reduced. 153 In addition to the reduced cell migration, γ-T3-treated breast cancer MDA-MB-231 and T-47D cells showed epithelial-mesenchymal transition.…”

“…119,123,153 In γ-T3-treated breast cancer MDA-MB-231 cells, cell migration machinery regulators such as RAC1 and WAVE2 signaling were reduced. 153 In addition to the reduced cell migration, γ-T3-treated breast cancer MDA-MB-231 and T-47D cells showed epithelial-mesenchymal transition. 119 Using the same in vitro assays, δ-T3 was also found to suppress the migration and invasion of non-small lung cancer cells 124 and colon cancer cells.…”

Potential Role of Tocotrienols on Non-Communicable Diseases: A Review of Current Evidence

“…The authors deciphered that γT3 caused significant reductions in cell invasion and migration. The suppression of Ras-related C3 botulinum toxin substrate 1 (Rac1)/Wiskott-Aldrich Syndrome protein-family verprolin-homologous protein 2 (WAVE2) signaling was proposed as the possible underlying mechanism (characterized by reduced expression of WAVE2, Arp2, Arp3, and reduced phosphorylation of Rac1/Cdc42) [395]. All these signaling molecules are essential for cytoskeletal reorganization, formation of membrane protrusions and raffles that promote cancer cell mobility [396].…”

γ-Tocotrienol Reversal of Epithelial-to-Mesenchymal Transition in Human Breast Cancer Cells is Mediated through a Suppression of Canonical Wnt and Hedgehog Signaling

“…Interestingly, numerous studies have shown that tocotrienols, but not tocopherols, have selective antiproliferative and apoptotic effects against various forms of breast cancer, while have little effect on normal mammary epithelial cell growth or function [14,15,25]. The anticancer Corn 112 ---0…”