p21-activated kinase group II small compound inhibitor GNE-2861 perturbs estrogen receptor alpha signaling and restores tamoxifen-sensitivity in breast cancer cells

Abstract

Estrogen receptor alpha (ERα) is highly expressed in most breast cancers. Consequently, ERα modulators, such as tamoxifen, are successful in breast cancer treatment, although tamoxifen resistance is commonly observed. While tamoxifen resistance may be caused by altered ERα signaling, the molecular mechanisms regulating ERα signaling and tamoxifen resistance are not entirely clear. Here, we found that PAK4 expression was consistently correlated to poor patient outcome in endocrine treated and tamoxifen-only treated breast cancer patients. Importantly, while PAK4 overexpression promoted tamoxifen resistance in MCF-7 human breast cancer cells, pharmacological treatment with a group II PAK (PAK4, 5, 6) inhibitor, GNE-2861, sensitized tamoxifen resistant MCF-7/LCC2 breast cancer cells to tamoxifen. Mechanistically, we identified a regulatory positive feedback loop, where ERα bound to the PAK4 gene, thereby promoting PAK4 expression, while PAK4 in turn stabilized the ERα protein, activated ERα transcriptional activity and ERα target gene expression. Further, PAK4 phosphorylated ERα-Ser305, a phosphorylation event needed for the PAK4 activation of ERα-dependent transcription. In conclusion, PAK4 may be a suitable target for perturbing ERα signaling and tamoxifen resistance in breast cancer patients.

Normal mammary gland development after MMTV-Cre mediated conditional PAK4 gene depletion

“…PAK4 is involved in a variety of cytoskeletal regulation such as promoting filopodia formation, dissolution of stress fibers, controlling actin polymerization and depolymerization as well as focal adhesion turnover [19][20][21][22][23][24][25] . Consistently, PAK4 overexpression is correlated with poor patient outcome in breast cancer patients, and its overexpression in breast cancer cell lines was shown to increase cell survival, anchorage-independent growth, cell migration and invasion [26][27][28][29][30] . PAK4 also plays an essential role during embryonic development, as complete depletion of PAK4 in mice caused embryonic lethality with severe defects in the heart, brain, and vasculature of the animals; however, its role in mammary gland development has not been investigated [31][32][33] .…”

“…Considering the known role of PAK4 in cell proliferation and invasion 26,37,38 , we next sought to determine the status of cell proliferation and expression of known markers for invasion within the mammary duct in virgin week 4 mice, a time point where the mammary epithelium is highly proliferative. To quantify cell proliferation within the duct, we labeled tissues for Ki67 and consistent with our previous results, lack of Pak4 did not alter cell proliferation in PAK4 MEp-/mice ( Fig.…”

Heat*seq: an interactive web tool for high-throughput sequencing experiment comparison with public data

“…An oestrogen receptor (ER) alpha ChIP-seq in MCF7 cells (Zhuang et al , 2015) comparison to the ENCODE TFBS dataset by sub-selecting ENCODE ER ChIP-seq experiments revealed that the binding pattern of ERα in MCF7 cells was more similar to its binding pattern in T-47D cells than in ECC-1 cells (Fig. 1A).…”

STAT1 facilitates oestrogen receptor α transcription and stimulates breast cancer cell proliferation

“…These ERα mutant forms recruit the co‐activators in the absence of oestrogen, while the affinity for ERα antagonists is also decreased . ERα protein activity is also regulated by various post‐translational modifications, such as phosphorylation and ubiquitination . Several studies have shown that certain modifications at the ERα hinge domain enhance ERα transcriptional activity and confer tamoxifen resistance .…”

“…[6][7][8] Several studies have shown that certain modifications at the ERα hinge domain enhance ERα transcriptional activity and confer tamoxifen resistance. 7,8 In addition to the active biological events in ERα signalling, a number of signalling pathways crosstalk with ERα via several effects. For example, numerous growth factor signalling kinases regulate ERα phosphorylation, including MAPK, RAS, AKT and PKA, [9][10][11] which subsequently enhance ERα stability or/and transcriptional activity and renders cells less sensitive to tamoxifen.…”