HDAC8 Activates AKT through Upregulating PLCB1 and Suppressing DESC1 Expression in MEK1/2 Inhibition-Resistant Cells.

Soon-Duck Ha,Shawn S C Li,Sung-Ouk Kim,Naomi Lewin

doi:10.3390/cells10051101

Abstract

Inhibition of the RAF-MEK1/2-ERK signaling pathway is an ideal strategy for treating cancers with NRAS or BRAF mutations. However, the development of resistance due to incomplete inhibition of the pathway and activation of compensatory cell proliferation pathways is a major impediment of the targeted therapy. The anthrax lethal toxin (LT), which cleaves and inactivates MEKs, is a modifiable biomolecule that can be delivered selectively to tumor cells and potently kills various tumor cells. However, resistance to LT and the mechanism involved are yet to be explored. Here, we show that LT, through inhibiting MEK1/2-ERK activation, inhibits the proliferation of cancer cells with NRAS/BRAF mutations. Among them, the human colorectal tumor HT-29 and murine melanoma B16-BL6 cells developed resistance to LT in 2 to 3 days of treatment. These resistant cells activated AKT through a histone deacetylase (HDAC) 8-dependent pathway. Using an Affymetrix microarray, followed by qPCR validation, we identified that the differential expression of the phospholipase C-β1 (PLCB1) and squamous cell carcinoma-1 (DESC1) played an important role in HDAC8-mediated AKT activation and resistance to MEK1/2-ERK inhibition. By using inhibitors, small interference RNAs and/or expression vectors, we found that the inhibition of HDAC8 suppressed PLCB1 expression and induced DESC1 expression in the resistant cells, which led to the inhibition of AKT and re-sensitization to LT and MEK1/2 inhibition. These results suggest that targeting PLCB1 and DESC1 is a novel strategy for inhibiting the resistance to MEK1/2 inhibition.

Highlights

Hyperactivation of the MEK1/2-ERK signaling axis due to mutations in NRAS and BRAF drives oncogenesis in ~30% of human cancers, and targeting RAF and MEK can be a curative therapy for these cancers [1]
These results suggest that targeting PLCB1 and DESC1 is a novel strategy for inhibiting the resistance to MEK1/2 inhibition
To further delineate the mechanisms of histone deacetylase 8 (HDAC8) in resistance to MEK1/2-ERK inhibition, we examined whether lethal toxin (LT) induces resistance and, if so, what mechanisms are involved in cancer cell types with known mutations in the RAS-RAF-MEK signaling axis

Summary

Introduction

Hyperactivation of the MEK1/2-ERK signaling axis due to mutations in NRAS and BRAF drives oncogenesis in ~30% of human cancers, and targeting RAF and MEK can be a curative therapy for these cancers [1]. We showed that macrophages adaptively respond to LT and become resistant to LT-induced cell cycle arrest through activating the phosphatidylinositol 3-kinase (PI3K)/AKT signaling cascade [13,14]. In certain tumor cells, resistance to RAF/MEK inhibitors is attributed to activation of the PI3K-AKT signaling axis caused by a loss of phosphatase and tensin homology (PTEN) or adaptive stress responses [15,16,17]. HDAC8 was shown to mediate the resistance to RAF inhibitors in melanoma [18] In these cells, HDAC8 deacetylates and activates the c-JUN transcription factor, resulting in the increased expression of receptor tyrosine kinases and ERK activation. To further delineate the mechanisms of HDAC8 in resistance to MEK1/2-ERK inhibition, we examined whether LT induces resistance and, if so, what mechanisms are involved in cancer cell types with known mutations in the RAS-RAF-MEK signaling axis. The inhibition of HDAC8 suppressed PLCB1 expression but enhanced DESC1 expression, both of which were involved in preventing the compensatory activation of AKT and resistance to MEK1/2 inhibition

Methods

Results

Conclusion